WO2014081761A1

WO2014081761A1 - Particles for uptake or sensing of oil and other applications, and related methods

Info

Publication number: WO2014081761A1
Application number: PCT/US2013/070896
Authority: WO
Inventors: David A. Weitz; Alireza ABBASPOURRAD; Nichlaus James CARROLL
Original assignee: Harvard University
Current assignee: Harvard University
Priority date: 2012-11-20
Filing date: 2013-11-20
Publication date: 2014-05-30
Anticipated expiration: 2015-05-20

Abstract

Various aspects of the present invention generally relate to particles for use in uptake or sensing of oil and other applications, and related methods. In some cases, such particles may be used to sense oil, e.g., in a subterranean oil reservoir. The particles may have a surface that is relatively hydrophilic and porous, and an interior that is relatively hydrophobic and is able to retain oil. Thus, when such particles are exposed to oil, some of the oil may be retained in the particles. Aspects of the invention are generally related to systems and techniques for making or using such particles, kits including such particles, or the like.

Description

PARTICLES FOR UPTAKE OR SENSING OF OIL AND OTHER

APPLICATIONS, AND RELATED METHODS

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Serial

No. 61/728,478, filed November 20, 2012, entitled "Particles for Uptake or Sensing Oil and Other Applications, and Related Methods"; and of U.S. Provisional Patent

Application Serial No. 61/730,026, filed November 26, 2012, entitled "Particles for Uptake or Sensing Oil and Other Applications, and Related Methods." Each of these is incorporated herein by reference in its entirety.

FIELD

The present invention generally relates, in certain aspects, to particles for use in uptake or sensing of oil and other applications, and related methods.

BACKGROUND

Porous particles are attractive for applications in drug delivery, sensing, and absorption of organic pollutants. Another important application is oil remediation, the removal of oil from undesirable sites, such as the surface of water or a sub-surface aquifer; innovation of materials for effective oil removal is essential to minimize ecological damage. Silica aerogels and core-shell nanoparticles have been used to this end; however, due to the hydrophobic nature of their surfaces, these particles are highly unstable in aqueous environments. Effective remediation requires particles that can remain stable in a variety of aqueous environments.

SUMMARY

The present invention generally relates, in certain aspects, to particles for use in uptake or sensing of oil and other applications, and related methods. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

Aspects of the present invention are directed to an article, e.g., comprising particles. The article, according to various embodiments, includes a particle comprising an outer region having an average pore diameter of between about 100 nm and about 500 nm, surrounding an inner region. In some cases, the inner region may comprise at least 5 wt oil therein, relative to the weight of the particle. In various embodiments, the particle comprises an inner region and a layer of nanoparticles substantially covering the surface of the particle. In some embodiments, the particle comprises at least 5 wt oil therein.

In various embodiments, the article comprises a particle comprising an inner region comprising a first polyacrylate, an outer region comprising a second polyacrylate, and a layer of nanoparticles substantially covering the surface of the particle. The article, in various embodiments, includes a particle comprising at least 5 wt oil therein, relative to the weight of the particle, wherein the particle further comprises a plurality of quantum dots. In various embodiments, the article comprises a particle comprising at least 5 wt oil therein, relative to the weight of the particle, wherein the particle further comprises a plurality of magnetically- susceptible nanoparticles.

According to certain embodiments, the article comprises oil droplets surrounded by jammed particles suspended in a fluid. In some cases, the jammed particles each comprise at least 5 wt oil from the oil droplets.

Aspects of the present invention are generally directed to a method. In accordance with various embodiments, the method includes acts of providing a droplet comprising a mixture of a monomer and a porogen, causing the mixture of the monomer and the porogen to begin phase separating, polymerizing the monomer to form a polymer prior to complete phase separation of the monomer and the porogen, and removing at least some of the porogen from the polymer.

In various embodiments, the method comprises acts of producing a droplet comprising a first half comprising a first phase and a second half comprising a second phase, and causing the second phase to completely surround the first phase within the droplet. In various embodiments, the method includes acts of flowing a first fluid in a first channel and a second fluid in a second channel, and expelling the first fluid from an exit opening in the first channel and the second fluid from an exit opening in the second channel each into the entrance opening of a third channel to form droplets within the third channel comprising a first half comprising the first fluid and a second half comprising the second fluid.

The method, in various embodiments, includes an act of determining the refractive index of a particle to determine an amount of oil contained therein. In various embodiments, the method comprises acts of exposing oil to magnetically-susceptible particles able to internally absorb the oil, and recovering at least some of the

magnetically- susceptible particles by exposing the particles to a magnet. In various embodiments, the method includes acts of exposing a particle to oil such that at least some of the oil is absorbed by the particle, removing at least 50 wt of the oil from the particle, and repeating the previous two steps at least once.

The method, in various embodiments, includes an act of injecting particles into a field suspected of containing a subterranean oil reservoir. In various embodiments, the particles comprise an inner region and a layer of nanoparticles substantially covering the surface of the particle.

The method, in various embodiments, includes an act of injecting particles into a field suspected of containing a subterranean oil reservoir. In various embodiments, the particles comprise an outer region having an average pore diameter of between about 100 nm and about 500 nm, surrounding an inner region.

Aspects of the present invention are generally directed to an apparatus for forming droplets. In some cases, the droplets may be multiple emulsion droplets. In various embodiments, the apparatus includes a first microfluidic channel having an exit opening, a second, adjacent microfluidic channel having an exit opening substantially coinciding with the exit opening of the first channel, and a third microfluidic channel having an entrance opening substantially opposing the exit openings of each of the first and second channels.

Aspects of the present invention encompass methods of making one or more of the embodiments described herein, for example, particles for absorbing or containing oil. Aspects of the present invention encompass methods of using one or more of the embodiments described herein, for example, particles for absorbing or containing oil.

Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control.

BRIEF DESCRIPTION OF THE DRAWINGS Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

FIGS. 1A-1B illustrate a particle in accordance with various embodiments of the invention, and a method of making the particle;

FIGS. 2A-2C illustrate additional particles and methods for making particles, in accordance with various embodiments of the invention;

FIGS. 3A-3F illustrate a structure of a particle in accordance with various embodiments of the invention;

FIG. 4 illustrates a ternary phase diagram in accordance with various

embodiments of the invention;

FIGS. 5A-5I illustrate various particles in accordance with various embodiments of the invention;

FIGS. 6A-6J illustrate certain particles containing oil, in accordance with various embodiments of the invention;

FIGS. 7A-7F illustrate various particles containing oil, in accordance with various embodiments of the invention;

FIGS. 8A-8F illustrate particles in accordance with various embodiments of the invention;

FIGS. 9A-9B illustrate a particle in accordance with various embodiments of the invention; and

FIG. 10 illustrates particles injected into the ground, in accordance with various embodiments of the invention.

DETAILED DESCRIPTION

Example of various embodiments of the invention are now described with respect to FIG. 1A. As will be discussed in more detail below, other configurations may be used as well in other embodiments. In this figure, particle 10 is shown having outer region 15 and inner region 20. Outer region 15 is generally hydrophilic or otherwise has properties that allow the particle to remain suspended in water or another aqueous fluid, e.g., when exposed to both aqueous and other immiscible fluids, such as an oil. In contrast, inner region 20 has a structure and/or composition that can be used to absorb oils or other hydrophobic materials. For example, inner region 20 may be porous, and/or be formed from hydrophobic or other materials that can absorb oils or other hydrophobic fluids.

In various embodiments, outer region 15 is porous. The porosity of outer region 15 may allow oils or other hydrophobic fluids that particle 10 is exposed to reach at least portions of inner region 20, e.g., through the pores of outer region 15. However, because outer region 15 is generally hydrophilic, particle 10 is able to stay suspended in aqueous fluid, even when particle 10 contains substantial amounts of oils or other hydrophobic fluids therein (e.g., within inner region 20).

In FIG. 1A, outer region 15 is depicted as a plurality of nanoparticles 18 substantially covering the surface of particle 10. However, it should be understood that this is by way of example only, and in other embodiments of the invention, other types of hydrophilic or other materials may be used to form outer region 15, for example, hydrophilic polymers. In this example, nanoparticles 18 may be formed from or comprise a relatively hydrophilic material, and/or be chemically treated to render the nanoparticles relatively hydrophilic, or otherwise allow the particle to remain suspended in water or aqueous fluid. For example, in various embodiments, nanoparticles 18 may include silica nanoparticles. In some embodiments, the silica nanoparticles may be chemically treated to more closely control their surface hydrophilicity.

The entire surface of particle 10 can be covered with nanoparticles 18, or there may be gaps in coverage of outer region 15 on the surface of particle 10 (e.g., to increase the amount of oil absorption). In addition, it should be noted that outer region 15 need not necessarily be a thin shell or monolayer of nanoparticles (or other materials) on the surface of particle 10. For example, outer region 15 can also extend deeper into the structure of particle 10 in other embodiments. For example, there may be a plurality of nanoparticles 18 present such that more than one layer of nanoparticles is present in particle 10, and/or such that not all of the nanoparticles are exposed to the surface of the particle

As mentioned, outer region 15 may be porous, such that fluids outside of particle 10 can contact at least a portion of inner region 20. However, outer region 15 need not always be porous in other embodiments of the invention; for example, there may be gaps or breaks in outer region 15 through which fluids outside of particle 10 can contact at least a portion of inner region 20. In the example shown in FIG. 1A, however, the porosity of outer region 15 is created by using nanoparticles 18, which leaves pores 16 open when the nanoparticles are packed together. However, despite the close-packing nature of nanoparticles 18 on the surface of particle 10 (e.g., as can be seen in the insert of FIG. 3B), there may still be residual pores that are created when nanoparticles 18 are packed closely together; this is due in part to the fact that nanoparticles 18 in this example are substantially spherical, and accordingly create pores or gaps even when the nanoparticles are packed tightly together. Thus, fluids outside of particle 10 can then contact at least a portion of inner region 20 through pores 16.

As is shown in FIG. 1A, inner region 20 can be divided into first portion 21 and second portion 22. However, it should be understood that it is not required that there be a separate first portion 21 and a second portion 22 in other embodiments of the invention; for instance, inner region 20 may be of a uniform composition, instead of exhibiting a first portion 21 and a second portion 22. In addition, it should be noted that in certain cases, there may not necessarily be a distinct interface between first portion 21 and second portion 22, e.g., first portion 21 and second portion 22 may represent two extremes of a continuous gradient in factors such as composition, porosity, etc.

In FIG. 1A, second portion 22 surrounds first portion 21, although this is not a requirement in all embodiments. In addition, it should be noted that first portion 21 and second portion 22 may not be symmetrically positioned within the particle, i.e., they are shown as being "off-center" such that the center of first portion 21 and second portion 22 do not coincide with the center of particle 10 (and indeed, they may not necessarily even coincide with each other, although some or all of these may in other embodiments). Each of first portion 21 and second portion 22 may independently have a structure and/or composition that can be used to absorb oils or other hydrophobic materials. For example, one or both may be relatively porous and/or be formed of relatively

hydrophobic polymers or other hydrophobic materials. In addition, in some cases, second portion 22 may be initially used to distribute nanoparticles 18 on the surface of particle 10, as will be explained below.

In certain embodiments, as shown here, first portion 21 comprises a first section 25 and a second section 26. As with first portion 21 and second portion 22, it should be understood that it is not required that there by a separate first section 25 and second section 26 in other embodiments of the invention; for instance, first portion 21 may have a uniform composition. In addition, there may not necessarily be a distinct interface between first section 25 and a second section 26; for instance, first section 25 and second section 26 may represent two extremes of a continuous gradient. Also, second section 26 is shown here as surrounding first section 25, although this likewise is not a requirement. In some embodiments, second section 26 and/or first section 25 may be "off-center" such that the center of first section 25 and second section 26 do not coincide with the center of particle 10, and/or the center of first portion 21, and/or with each other (although some or all of these may in other embodiments).

In some embodiments, first section 25 has a higher porosity than second section

26. As is discussed in detail below, in some instances, a porogen is used to create pores 29 in first portion 21, and in some cases, the porogen may concentrate within first portion 21 such that, when the porogen is later removed, a first location of first portion 21 (i.e., first section 25) may have a higher porosity than a second location of first portion 21 (i.e., second section 26). The porogen may be used to create locations within particle 10 (e.g., within inner region 20, including in first portion 21 and/or second portion 22) that can be used to contain oils or other hydrophobic materials that are absorbed by the particle. Various techniques for creating such locations using a porogen during formation of the particles are discussed in detail below.

In addition, in some cases, the porogen may concentrate within first portion 21 to such a degree that the porogen forms an essentially continuous phase surrounding one or more discrete phases of the one or more relatively hydrophobic polymers or other hydrophobic materials, shown here as isolated phases 27 within a continuous opening 28 that are created once the porogen is removed. As mentioned, some of the oil or other hydrophobic materials that are absorbed by the particle may collect within opening 28 within particle 10 (as well as in other locations, e.g., pores 29 within second portion 26). Thus, when the porogen is then removed, the final particle may exhibit one or more locations free of any material that can be used to contain oils or other hydrophobic materials absorbed into the particle.

Referring now to FIG. IB, an example method of forming particles such as those discussed above is now discussed. However, it should be understood that in various embodiments of the invention, other methods of forming such particles may be used. For example, in various embodiments of the invention, one or more multiple emulsion droplets may be formed using various techniques, where the droplets contain precursors that can be solidified to form particles such as those discussed herein. A variety of techniques for forming multiple emulsion droplets will be known by those of ordinary skill in the art, many of which can be used to form particles, as discussed herein.

FIG. IB shows microfluidic device 50 comprising a theta (Θ) shaped glass capillary 55 with first channel 51 and second channel 52, forming the upper and lower halves of glass capillary 55, divided by a wall of material. At the end of glass capillary 55, each of first channel 51 and second channel 52 ends at respective exit openings 53 and 54, having the general appearance of the Greek letter theta. Although a theta capillary is shown here, in other embodiments, other configurations may be used, for example two separate microfluidic channels with exit openings near each other.

Exiting from first channel 51 is a first fluid 61, and exiting from second channel 52 is a second fluid 62. First fluid 61 and/or second fluid 62 may contain monomers that can be polymerized at a later time, as discussed below. In addition, in this example, second fluid 62 contains nanoparticles 18. In some cases, nanoparticles 18 can be (although need not be) suspended and evenly distributed within second fluid 62.

Similarly, first fluid 61 may contain a porogen (not shown here). The porogen may, in some instances, be evenly distributed within first fluid 61.

As is shown in FIG. IB, first fluid 61 and second fluid 62 exit first channel 51 and second channel 52 through respective exit openings 53 and 54 into continuous channel 70 containing continuous fluid 75. As each of first fluid 61 and second fluid 62 is substantially immiscible with continuous fluid 75 (at least on the time scale of forming droplets), first fluid 61 and second fluid 62 condense together to form droplet 69 within continuous fluid 75. However, because first fluid 61 and second fluid 62 may also be substantially immiscible with each other (again, at least on the time scale of forming droplets), the fluids do not mix with each other, but instead form distinct phases within droplet 69. Although shown here, droplet 69 contains symmetrical halves of first fluid 61 and second fluid 62, this is solely by way of example; in other embodiments, depending on the relative flow rates of first fluid 61, second fluid 62, and continuous fluid 75, one fluid or the other may be present in a larger amount or volume within droplet 69, and/or their division may not necessary be symmetric within droplet 69.

It should also be noted that in FIG. IB, exit openings 53 and 54 of first channel 51 and second channel 52 are positioned within and substantially oppose the entrance opening 83 of third channel 80, through which droplets 69 suspended within continuous fluid 75 are able to enter. However, it should be noted that this configuration is by way of example only, and other configurations may be used to collect droplets 69 exiting first channel 51 and second channel 52, for example dimensional restrictions or other configurations such as those described in International Patent Publication Number WO 2006/096571, filed March 3, 2006, entitled "Method and Apparatus for Forming

Multiple Emulsions," by Weitz et ah, incorporated herein by reference in its entirety.

In this particular example, in third channel 80, first fluid 61 and second fluid 62 adopt a different configuration within droplet 69. Without wishing to be bound by any theory, it is believed that this rearrangement may occur, for example, due to differences in surface energy or surface tension between first fluid 61 with continuous fluid 75, and second fluid 62 with continuous fluid 75, i.e., this rearrangement of fluids may occur to minimize surface energy within droplet 69. Thus, as is shown here, first fluid 61 may move away from continuous fluid 75 such that second fluid 62 is able to surround first fluid 61 (in some cases such that continuous fluid 75 and first fluid 61 no longer directly physically contact each other), in order to minimize this surface energy.

In addition, a similar process can occur with second fluid 62, containing nanoparticles 18. In this particular example, due to differences in surface energy or surface tension between second fluid 62 and continuous fluid 75, and nanoparticles 18 and continuous fluid 75, rearrangement of nanoparticles 18 within second fluid 62 may occur, for instance, such that at least some of nanoparticles 18 are driven to the surface of droplet 69. If enough nanoparticles 18 are present, at least some of nanoparticles 18 can form at least a surface layer or coating on the surface of droplet 69 (and optionally, further layers of nanoparticles if enough nanoparticles are present).

In various embodiments of the invention, a porogen within first fluid 61 can also be induced to form a separate phase within first fluid 61, e.g., due to relatively low miscibility with first fluid 61. However, depending on factors such as fluid viscosity, the phase separation may proceed at a relatively slower pace. Thus, although

thermodynamically, complete phase separation of first fluid 61 and the porogen is favored, due to kinetics, incomplete phase separation can occur as is depicted in FIG. IB, where some of the porogen has condensed to form a separate phase (potentially containing therein droplets of first fluid 61), and likewise, first fluid 61 may still contain droplets of porogen that have not yet reached the condensed porogen phase.

As shown in FIG. IB, this process may be arrested before complete phase separation occurs, e.g., by causing monomers within first fluid 61 and/or second fluid 62 to polymerize, e.g., to form particle 10. As is shown here, polymerization may occur through exposure to ultraviolet light 77, although in other embodiments, other methods of polymerization, for example, chemical initiators, may be used, in addition or instead of ultraviolet light.

Accordingly, as shown here, once the components of droplet 69 have been polymerized to form particle 10, nanoparticles 18 are present on the surface of particle 10 to form outer region 15 (creating pores 16 due to gaps present when nanoparticles 18 are packed together on the surface of particle 10), while the remaining polymers form inner region 20 of particle 10. Inner region 20 can be subdivided into a first portion 21 and a second portion 22, created by the polymerization of monomers within first fluid 61 and second fluid 62, respectively, with second fluid 62 surrounding first fluid 61.

Second portion 22 (created from second fluid 62) can also contain additional

nanoparticles 18 that were not able to move to the surface of particle 10, e.g., because there was insufficient room for those nanoparticles, and/or due to kinetic effects (for instance, because not all of the nanoparticles were able to move to the surface prior to polymerization). In addition, first portion 21 (created from first fluid 61) may also be subdivided into a first section 25 and a second section 26, with second section 26 surrounding first section 25. While both first section 25 and second section 26 may each contain polymerized monomer from first fluid 61 and the porogen, first section 25 may be enriched in the porogen relative to polymer, while second section 26 may be enriched in monomer relative to the porogen.

The porogen may also be removed from the particle, thereby creating locations within particle 10 that can be used to contain oils or other hydrophobic fluids therein. See, e.g., FIG. 3 A. Pores may be created in one or both of first section 25 and second section 26 due to the presence of porogen in both of those sections (for instance, due to incomplete phase separation); it should be noted that if too much phase separation occurs, the porosity within second section 26 will be less, making it more difficult for oil or hydrophobic fluids to reach first section 25. Any suitable technique may be used to remove the porogen, depending on the type of porogen used, for example, extraction using a liquid solvent, thereby creating the final particle.

The preceding example shows a particle of various embodiments of the invention, and a technique for forming that particle. However, it should be understood that the invention is not limited only to these particles and techniques, and that other embodiments are also possible, as is discussed herein.

Such particles may be used for a wide variety of applications, in various aspects of the present invention, including but not limited to oil uptake and/or sensing of oil. For instance, as an example of an application involving the sensing of oil, the particles can be exposed to oil or other hydrophobic fluids, which may enter or become trapped within the particles. By determining the oil (or other hydrophobic fluids) within the particles, the oil that the particles was exposed to may be determined or analyzed.

Any suitable method may be used to determine the oil or other hydrophobic fluids within the particles. For example, in various embodiments, optical methods may be used, e.g., determining the transparency or refractive index of the particle. In various embodiments, changes in weight of the particles are determined to determine the amount of oil or other hydrophobic fluids trapped within the particles. In various embodiments, the oils or other hydrophobic fluids are extracted or recovered from within the particles, for example, by exposure to organic fluids such as isopropanol. In addition, in some cases, after extraction of the oils or other hydrophobic fluids, the particles can also be recycled or reused in some cases, as discussed below.

In various embodiments, the particles may be exposed to any location believed to contain oil, e.g., for sensing applications. The oil that the particles are exposed to is not limited herein to only crude oil, but also may include, in other embodiments, any other types of oils. Various non-limiting examples of oils are discussed herein. The location may be, for example, a subterranean oil reservoir, a water supply (e.g., to look for oil leaks therein), a factory or a manufacturing process, a laboratory experiment, etc. For example, in various embodiments, such particles are injected into a well into a subterranean oil reservoir (or at least a location suspected of containing a subterranean oil reservoir), and some of the particles can then be recovered and analyzed as discussed herein to determine the presence, quantity, and/or type of oil present. In some cases, the particles may be injected into a first location and recovered from the same or different locations (e.g., the particles may be injected into a first location and recovered from the same location, and/or from 2 or more other locations. For example, a field surrounding an injection well suspected of containing a subterranean oil reservoir may be mapped by injecting such particles into the injection well, then recovering the particles from other wells around the field. In addition, in some embodiments, the particles can be labeled, for example, with determinable species such as quantum dots or fluorescent molecules, so that different particles (e.g., having abilities to recover different types of oil or other hydrophobic fluids) can be distinguished.

In some embodiments, the particles are injected into a subterranean oil reservoir, which may include, for example, deep wells, rocks, soil, etc. However, it should be noted that embodiments of the present invention are not limited to delivery of particles to crude oil contained in the ground, e.g., within a subterranean oil reservoir. In other embodiments, particles can be delivered to any suitable hydrocarbons or oil, including crude oil or petroleum, whether within the ground or not in the ground, synthetic or natural, purified or unpurified, refined or unrefined, treated or untreated, etc.

A non-limiting example is now discussed with reference to FIG. 10. In this figure, within the ground, or any geological formation, 100 is suspected a subterranean oil reservoir 110. An injection well 105 is dug at a first location, near the location where the subterranean oil reservoir is suspected to be. Within the well 105, particles such as those discussed herein are injected into the ground 100. Subsequently, some of the particles may be recovered, e.g., through the well 105, and/or through one or more recovery wells 115. In addition, in other embodiments, more than one injection well may be used, e.g., with the same or different particles.

The recovered particles may be analyzed, for example, to determine the amount of oil contained within the particles. Various examples of determining the oil contained within the particles are discussed in detail herein, for example, determining changes in the weight or the refractive index of the particles. Based on the amount of oil contained within the recovered particles, and knowledge of where the particles were originally injected into the ground 100, information about the subterranean oil reservoir 110 may be determined, for example, the location of the reservoir, the type of oil contained within the reservoir, or the like.

In addition, in some cases, more than one type of particle may be injected into the injection well 105, e.g., to different depths within the ground 100. For example, the particles may include different determinable species, e.g., a first species for particles injected to a first depth 107 and a second species for particles injected to a second depth 108, that can be distinguished from each other using the determinable species. Non- limiting examples of determinable species include quantum dots or fluorescent molecules such as those discussed herein. Recovery of such particles, e.g., through the injection well 105 and/or the recovery wells 115, with knowledge of where the particles were initially injected (e.g., at depth 107 or 108), may be used, for instance, to determine the depth or size of the subterranean oil reservoir 110, to determine changes in composition as a function of location within the subterranean oil reservoir 110, or the like.

Similarly, in various embodiments, such particles may be injected or delivered to a water supply (e.g., municipal water or a water in or from a factory), and some of the particles can be recovered and analyzed as discussed herein to determine the presence, quantity, type, etc. of oil present, e.g., at various locations. As above, in some cases, the particles may be labeled, for example, with determinable species.

In certain embodiments, some or all of the particles are recycled or reused. For example oils or other hydrophobic fluids present within the particles may be extracted or recovered from within the particles, for example, by exposure to organic fluids such as isopropanol. In some cases, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the oils or other hydrophobic fluids may be removed from the particles, and the particles can then be recycled and reused. This may be particularly useful, for example, in applications such as oil recovery or oil spill clean up, where the same particles may be used to absorb oil, the oil may be recovered from the particles, and the particles reused to absorb more oil. This cycle can also be repeated multiple times, e.g., to recover the oil.

In various embodiments, the particles may be used to recover oil, e.g., from an oil reservoir, from an oil spill, or to decontaminate water (or another fluid), or the like. The particles can also be reused in some instances, as noted herein. For example, the particles may be exposed to a fluid or location comprising oil, and after some of the oil is absorbed into the particles as discussed herein, the particles may be removed from the fluid. As non-limiting examples, the particles may be used to clean up a surface oil spill (e.g., an oil spill on ocean water or fresh water), the particles may be injected and recovered from a subterranean oil reservoir, the particles may be injected to a water supply (e.g., to clear up oil contaminants or an oil spill therein), the particles may be injected into a fluid (not necessarily water) in order to remove oil (e.g., in a

manufacturing process, such as for a pharmaceutical compound), or the like.

Any of a large variety of techniques can be used to remove the particles, e.g., after absorption of the oil or other hydrophobic fluids has occurred. For example, the particles may be removed using filtration, sedimentation, buoyancy, centrifugal forces, or the like. In another embodiment, the particles are removed using magnetic forces, for example, if the particles comprise magnetically susceptible species include iron oxide, magnetite, hematite, other compounds containing iron, or the like. Thus, for example, a fluid (e.g., water or another aqueous fluid) containing oil and particles able to absorb the oil can then be exposed to a suitable magnetic field able to attract at least some of the particles, e.g., to recover those particles.

In addition, in some cases, such particles may recover oil (or other hydrophobic fluids), not only through absorption, but also through particle "jamming," where the particles surround droplets of oil (or other hydrophobic fluids) to such a degree that the particles essentially form a hard "shell" around the oil. In some cases, the jammed droplets surround the droplets to such a degree that the droplets may become distorted or non- spherical. In addition, the shell of particles itself may be removed, often as a single mass (e.g., via filtration) to remove the oil droplets.

Aspects of the present invention are generally directed to particles that can absorb oils or other hydrophobic materials. Such particles may be used for a variety of applications, including but not limited to, sensing of oils or other hydrophobic materials, uptake of oils or other hydrophobic materials, or the like. As non-limiting examples, such particles may be injected into a subterranean oil reservoir to determine the presence, quantity, and/or type of oil in the reservoir; the particles may be used to absorb oil mixed with water, for example, in an oil spill; or the particles may be used as tracers to monitor the amount of oil present in water, for example, to look for contaminants in municipal water. Other examples of such uses will be discussed in more detail below.

As mentioned, the particles may be applied to a variety of oils or other hydrophobic materials in various embodiments of the invention. It should be understood that, as used herein, an "oil" is not intended to be limited to only crude oil, but also may include, in other embodiments, any fluid that is hydrophobic and is not substantially miscible in water and is liquid at a temperature where water is also liquid. Non-limiting examples of oils include, in addition to crude oil or petroleum, hydrocarbons (substituted or unsubstituted) such as ethane, propane, butane, etc. In addition, in some cases, the particles may be used with other types of hydrophobic materials, such as waxes, fats, or the like.

As used herein, "crude oil" is used to refer to petroleum and all other

hydrocarbons, regardless of molecular weight or composition, produced from a well in the ground. Typically, the crude oil is a liquid, although in some cases, the crude oil may also be recovered as a solid or a semi-solid (e.g., a sludge). The systems, articles, and methods described herein may be used, in some cases, to sense or uptake any type of crude oil, as is discussed herein. As non-limiting examples, the crude oil may include "heavy" crude oil (American Petroleum Institute gravity ("API gravity") of 20 degrees or less), "intermediate" crude oil (API gravity of between 20 degrees and 40.1 degrees), and/or "light" crude oil (API gravity of 40.1 degrees or greater). API gravity is, generally, a measure of density, and those of ordinary skill in the art will be able to determine the API gravity of a sample of crude oil. As another example, the systems, methods, and articles described herein may be configured to deliver fluids and/or agents to sweet crude oil (i.e., oil containing less than 0.5 wt% sulfur) and/or sour crude oil (i.e., oil containing 0.5 wt% or more of sulfur).

The particles may be of any shape or size, and if more than one particle is present, the particles may be of substantially the same shape and/or size, and/or different shapes and/or sizes, depending on the application. The particles may be substantially spherical, or non-spherical in some cases. Those of ordinary skill in the art will be able to determine the average cross-sectional diameter of a single particle and/or a plurality of particles, for example, using laser light scattering, microscopic examination, or other known techniques. The average cross- sectional diameter of a single particle, in a non- spherical particle, is the diameter of a perfect sphere having the same volume as the non- spherical particle. The average cross-sectional diameter of a particle (and/or of a plurality or series of particles) may be, for example, less than about 1 cm, less than about 5 mm, less than about 2 mm, less than about 1 mm, less than about 500 micrometers, less than about 200 micrometers, less than about 100 micrometers, less than about 75 micrometers, less than about 50 micrometers, less than about 25 micrometers, less than about 10 micrometers, or less than about 5 micrometers, or between about

50 micrometers and about 1 mm, between about 10 micrometers and about

500 micrometers, or between about 50 micrometers and about 100 micrometers in some cases. The average cross-sectional diameter may also be at least about 1 micrometer, at least about 2 micrometers, at least about 3 micrometers, at least about 5 micrometers, at least about 10 micrometers, at least about 15 micrometers, or at least about 20

micrometers in certain cases. In some embodiments, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the particles within a plurality of particles has an average cross-sectional diameter within any of the ranges outlined in this paragraph. Thus, the plurality of particles may have relatively uniform cross- sectional diameters in accordance with some embodiments.

In some embodiments, the plurality of particles has an overall average diameter and a distribution of diameters such that no more than about 5%, no more than about 2%, or no more than about 1% of the particles have a diameter less than about 90% (or less than about 95%, or less than about 99%) and/or greater than about 110% (or greater than about 105%, or greater than about 101%) of the overall average diameter of the plurality of particles. In certain embodiments, the plurality of particles has an overall average diameter and a distribution of diameters such that the coefficient of variation of the cross- sectional diameters of the particles is less than about 10%, less than about 5%, less than about 2%, between about 1% and about 10%, between about 1% and about 5%, or between about 1% and about 2%. The coefficient of variation (c_v) can be determined by those of ordinary skill in the art, and may be defined as:

wherein σ (sigma) is the standard deviation and μ (mu) is the mean.

In addition, in certain instances, the particles may be of substantially the same shape and/or size (i.e., "monodisperse"), or of different shapes and/or sizes, depending on the particular application. In some cases, the particles may have a homogenous distribution of cross-sectional diameters, i.e., the particles may have a distribution of cross- sectional diameters such that no more than about 10%, about 5%, about 3%, about 1%, about 0.03%, or about 0.01% of the particles have an average diameter that is more than about 10%, about 5%, about 3%, about 1%, about 0.03%, or about 0.01% different from the average cross- sectional diameter of the particles.

The particles themselves may be formed from any suitable materials, and often include more than one type of material, for example, a hydrophilic material and a hydrophobic material. Typically, a material is "hydrophobic" when a droplet of water forms a contact angle greater than 90° when placed in intimate contact with the material in question in air at 1 atm and 25 °C. A material is "hydrophilic" when a droplet of water forms a contact angle of less than 90° when placed in intimate contact with the material in question in air at 1 atm and 25 °C. The "contact angle," in the context of hydrophobicity and hydrophilicity is the angle measured between the surface of the material and a line tangent to the external surface of the water droplet at the point of contact with the material surface, and is measured through the water droplet.

In various embodiments, all, or at least a portion of, the outer surface or region of the particle is generally hydrophilic, or otherwise has properties that allow the particle to remain suspended in water or another aqueous fluid. In some cases, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the outer surface of the particle exhibits such properties. The particle, in some cases, comprises an outer region that provides such hydrophilic properties. In some embodiments, the outer surface of the particle may comprise one or more materials that is hydrophilic, and/or the outer surface of the particle may comprise one or more materials that have been treated (e.g., chemically) to render the materials hydrophilic. For instance, the material may comprise a hydrophilic polymer such as polyethylene glycol or polypropylene glycol, or the material may be a polymer that has been reacted or coated with a hydrophilic polymer such as polyethylene glycol or polypropylene glycol.

In various embodiments, the outer surface or region of the particle may comprise one or more nanoparticles. The nanoparticles may fully or partially cover the outer surface of the particle. For example, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the outer surface of the particle may be covered with nanoparticles. The nanoparticles may be generally hydrophilic, thereby allowing the particle to remain suspended. The nanoparticles may be

substantially spherical and have an average diameter of less than about 1 micrometer, e.g., less than about 1000 nm, less than about 500 nm, less than about 300 nm, less than about 100 nm, less than about 50 nm, less than about 30 nm, less than about 10 nm, etc. The nanoparticles can also be of substantially the same size (e.g., having the size distributions and/or coefficients of variation previously discussed), although in certain cases, the nanoparticles may have varying sizes, e.g., to increase porosity.

The nanoparticles can be formed from a variety of materials, and the

nanoparticles may all have substantially the same or different compositions. In various embodiments, at least some of the particles are hydrophilic, e.g., formed from

hydrophilic materials and/or be treated (e.g., chemically) to render the nanoparticles at least partially hydrophilic. For instance, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the nanoparticles may be hydrophilic. The hydrophilic nanoparticles, in some cases, are formed from hydrophilic polymers such as polyethylene glycol or polypropylene glycol, and/or the hydrophilic polymers may be treated with a surface coating of hydrophilic polymers such as polyethylene glycol or polypropylene glycol. In various embodiments, at least some of the hydrophilic nanoparticles can be formed from inorganic materials such as silica (Si0₂). Silica is particularly useful, in some embodiments, since it can be treated, e.g., to module the hydrophilicity of the nanoparticles or to add additional functionality to the nanoparticles. In some embodiments, the outer region of the particle is substantially porous. It should be noted, however, that this is not necessarily a requirement; for example, in some cases, only a portion of the outer region is generally hydrophilic, or the particle may otherwise be structured such that hydrophobic regions are exposed to the outer surface of the particle, e.g., such that fluids external of the particle can come into contact with those hydrophobic regions.

In certain embodiments, the outer region of the particle has a porosity such that hydrophobic or inner regions of the particle have at least some exposure to the outer surface of the particle, e.g., through such pores. For instance, fluids (e.g., oils or other hydrophobic materials) external of the particle can penetrate through such pores to come into contact with those regions. For example, in various embodiments, the particles have an average pore diameter of less than about 1 micrometer, e.g., less than about 1000 nm, less than about 500 nm, less than about 300 nm, less than about 100 nm, less than about 50 nm, less than about 30 nm, less than about 10 nm, etc. In addition, in some cases, the average pore diameter can be at least about 10 nm, at least about 20 nm, at least about 30 nm, at least about 50 nm, at least about 100 nm, at least about 200 nm, at least about 300 nm, at least about 500 nm, etc.

Any technique may be used to create such porosity in the outer region of the particle. For example, in various embodiments, a porogen may be present within the outer region during its formation, which is then removed to yield such pores. Non- limiting examples of porogens include those discussed herein. In addition, in some embodiments, pores can be created by using nanoparticles in the outer region of the particle. Such nanoparticles, even when closely packed on the surface of the particle (e.g., as is shown in the insert of FIG. 3B), may have residual gaps between the nanoparticles, e.g., if the nanoparticles as substantially spherical, which thereby define pores on the surface of the particle. In addition, such pore sizes can be readily controlled, e.g., by controlling the sizes of the nanoparticles.

The inner region of the particle, in accordance with various embodiments, is selected to have a structure and/or composition that can be used to absorb oils or other hydrophobic materials. For instance, the inner region may have a porosity (which may or may not be uniform) within the inner region that allows oils or other hydrophobic materials to enter and be retained within the particle (for example, due to capillary action), and/or the inner region can have a composition that allows oils or other hydrophobic materials to enter therein. For example, the inner region may comprise one or more hydrophobic materials that can be used to absorb oils or other hydrophobic materials.

In various embodiments, the inner region comprises one or more polymers, which may be blended together, or form discrete portions within the particle. Some or all of the polymers may be hydrophobic in some cases. Examples of such polymers include, but are not limited to, polyacrylates, polystyrene ("PS"), polycaprolactone ("PCL"), polyisoprene ("PIP"), poly(lactic acid), polyethylene, polypropylene, polyacrylonitrile, polyimide, polyamide, and/or mixtures and/or co-polymers of these and/or other polymers. The polymers may have any suitable molecular weights, for example, relatively high weight- averaged molecular weights (e.g., greater than about 20,000 g/mol, e.g., between about 20,000 g/mol and about 800,000 g/mol). As discussed below, in some embodiments, some or all of the polymers can be formed by causing monomers within a droplet to polymerize, e.g., upon exposure to ultraviolet light.

In some embodiments, some or all of the inner region may be porous. In some cases, the inner region can comprise different portions having the same or different porosities. The inner region may be porous such that oils or other hydrophobic materials may be contained within the particle, e.g., within the pores of the inner region. For instance, the inner region can comprise polymers or other materials that are relatively hydrophobic or otherwise allow oil entering the particle to remain within the particle, e.g., within the pores, due to favorable hydrophobic interactions between the oils or other hydrophobic materials and the polymers or other materials of the inner region. The polymers or other materials can also exhibit a water contact angle of greater than 90° in some embodiments. In some cases, the inner region of the particle has a porosity such that the void volume of the particle (as defined by the pores of the inner region) is at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, or at least about 50%.

The pores can have any shape and size, and may be uniformly distributed within the inner region, or may be distributed such that different portions having the same or different porosities. In some cases, the pores in the inner region (or at least in one portion of the inner region) have an average pore diameter of less than about 1 micrometer, e.g., less than about 1000 nm, less than about 500 nm, less than about 300 nm, less than about 100 nm, less than about 50 nm, less than about 30 nm, less than about 10 nm, etc. In addition, in some cases, the average pore diameter may be at least about 10 nm, at least about 20 nm, at least about 30 nm, at least about 50 nm, at least about 100 nm, at least about 200 nm, at least about 300 nm, at least about 500 nm, etc.

In addition, as discussed herein, in accordance with certain embodiments, various particles are used to retain oils or other hydrophobic materials. Thus, in certain embodiments, the pores may contain such oils or other hydrophobic materials. For example, at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or about 100% (by volume) of the pores can be filled with such oils or other hydrophobic materials. In addition, in some embodiments, the particle may contain oils or other hydrophobic materials in amounts of at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or at least about 100%, relative to the weight of the particle.

In various embodiments, the inner region may comprise at least a first portion and a second portion, where the first and second portions are compositionally distinct, e.g., comprising different polymers, different porosities, etc. For example, the first and second portions may comprise different polymers, or the same polymers but with substantially different average molecular weights, or the first and section portions may comprise the same polymers, but exhibiting different porosities. In addition, in some embodiments, other portions can also be present (for example, having differing compositions), or there may be gradient in composition between the first portion and the second portion.

If more than one such portion is present, the portions may or may not necessarily be symmetrically positioned within the particle, i.e., one or more of the portions may be "off center" such that the center of the portion may not coincide with the center of the particle. In addition, in various embodiments, the centers of one or more of the portions may not necessarily coincide with the centers of other portions within the particle. In some embodiments, as discussed below, the second portion can partially or completely surround the first portion of the particle. For instance, the second portion may completely surround the first portion such that the first portion does not contact the surface of the particle. In other embodiments, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the first portion may be surrounded by the second portion. In addition, the first portion may be "off center" with respect to the second portion in some cases, i.e., the center of the first portion and the center of the second portion may not necessarily coincide.

If the inner region comprises at least a first portion and a second portion, the first portion and a second portion can be present in any suitable ratio. For example, the weight ratio of the first portion to the second portion can be between about 0.1 and about 10, between about 0.2 and about 5, between about 0.5 and about 2, between about 0.5 and about 1.5, between about 0.8 and about 1.2, or between about 0.9 and about 1.1. In some cases, the weight ratio of the first portion to the second portion may be about 10: 1, 8: 1, 5: 1, 4: 1, 3: 1, 2: 1, 1: 1, 1:2, 1:3, 1:4, 1:5, 1:8, or 1: 10.

In various embodiments, the first portion and the second portion can each comprise a different polymer or overall polymer composition. The polymers may be selected such that the two polymers are each relatively hydrophobic or exhibit a water contact angle of greater than 90°, but that prior to polymerization, the polymers can be contained in two fluids that are relatively immiscible, at least on the time scale of forming droplets and polymerizing them. For example, one or more polymers may be polymerized upon exposure to ultraviolet radiation, e.g., if one or more polymers is a UV-crosslinkable polymer. As a non-limiting example, in various embodiments, the second portion may include or be defined by an acrylate, such as ethoxylated

trimethylolpropane triacrylate (which can be polymerized to form poly(ethoxylated trimethylolpropane triacrylate, which is generally hydrophobic), but is not immiscible with certain other types of acrylates, such as isobornylmethaacrylate (which can be polymerized to form poly(isobornylmethaacrylate), which is generally hydrophobic).

The second portion, in various embodiments, can be used to assist in distributing or rearranging nanoparticles on the surface of the particle during formation of the particle. In some cases, however, there may also be some nanoparticles present within the second portion, e.g., not necessarily present on the surface of the particle. For example, the second portion can be formed from polymers or other materials that nanoparticles can be suspended in, and that can be polymerized or otherwise solidified to form a relatively hydrophobic polymer or other materials. In addition, in some embodiments, the second portion may be relatively porous, e.g., due inherently to the polymerization of the second portion, due to the presence of porogens that are subsequently removed, or the like. For instance, the second portion can have any of the porosities and/or void volumes described herein.

The first portion may be porous such that oils or other hydrophobic materials may be contained therein, and/or the first portion can be formed from polymers or other materials that are relatively hydrophobic or otherwise allow oil entering the particle to remain within the particle, e.g., in the first portion. The polymers or other materials can also exhibit a water contact angle of greater than 90° in some cases. In addition, in some embodiments, the first portion can be relatively porous, e.g., due inherently to the polymerization of the first portion, due to the presence of porogens that are subsequently removed, or the like. For example, the first portion may have any of the porosities and/or void volumes described herein, e.g., a void volume of at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, etc.

In various embodiments, the first portion comprises a first section and a second section, where the first section has a higher porosity or void volume, relative to second section. This can be created, for example, by the use of a porogen that is able to substantially concentrate within the first section, e.g., due to immiscibility or other effects. When the porogen is removed, sections within the first portion where the porogen was concentrated may have a higher porosity or void volume, relative to other sections within the first portion. In some cases, the porogen can be sufficiently concentrated such that the porogen forms an essentially continuous phase, which can then be removed to create a section within the first portion that is essentially hollow, or has a relatively high void volume. For example, in some embodiments, there may be some amounts of residual polymer or other material still present within this section.

In some embodiments, the second section may partially or completely surround the first section. For instance, the second section may completely surround the first section such that the first section, or at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the first section may be surrounded by the second section. In addition, the first section can be "off center" with respect to the second section in some cases, i.e., the center of the first section and the center of the second section may not necessarily coincide.

In addition, in various embodiments, the first portion has a first section having a relatively high porosity or void volume, and a second section having a relatively low porosity or void volume. In other cases, other sections can also be present (e.g., having differing porosities or void volumes), or there may be gradient in porosities or void volumes between the first section and the second section.

In various embodiments, the first section or the second section has an average pore diameter of less than about 1 micrometer, e.g., less than about 1000 nm, less than about 500 nm, less than about 300 nm, less than about 100 nm, less than about 50 nm, less than about 30 nm, less than about 10 nm, etc. In addition, in some cases, the average pore diameter may be at least about 10 nm, at least about 20 nm, at least about 30 nm, at least about 50 nm, at least about 100 nm, at least about 200 nm, at least about 300 nm, at least about 500 nm, etc. The first section or the second section can also have any of the porosities and/or void volumes described herein, e.g., a void volume of at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, etc.

In addition, in some embodiments, other species may be present within the particles, e.g., in one or more regions, portions, or sections within the particle. For instance, in various embodiments, the particles can include a determinable species, for example, quantum dots or fluorescent molecules, which can be used to identify particles. As a non-limiting example, a plurality of particles may be exposed to different environments or conditions, and the particles can be readily determined or distinguished, for instance, using the determinable species. Quantum dots or fluorescent molecules can be readily obtained commercially.

As another example, the particles may include magnetically susceptible species. The species may be used, for example, to allow separation of the particles magnetically. Thus, for example, a magnetic field may be used to separate the magnetically-susceptible particles from other, non-magnetically- susceptible particles, from a liquid solution, or the like. Non-limiting examples of magnetically susceptible species include iron oxide, magnetite, hematite, other compounds containing iron, or the like. In various

embodiments, the magnetically susceptible species is present as one or more

nanoparticles.

Aspects of the present invention are generally directed to systems and techniques for making particles such as those described herein. For example, in various

embodiments, multiple emulsions can be created comprising various monomers or other species that can be polymerized or otherwise solidified to create the particles. In general, multiple emulsions are emulsions that are formed with more than two fluids, or two or more fluids arranged in a more complex manner than a typical two-fluid emulsion, e.g., comprising a first droplet, surrounded by a second droplet (optionally surrounded by a third droplet, etc.), contained within a continuous phase.

Various techniques for forming multiple emulsions are known by those of ordinary skill in the art, and include those disclosed in International Patent Publication Number WO 2006/096571, filed March 3, 2006, entitled "Method and Apparatus for

Forming Multiple Emulsions," by Weitz et al. ; International Patent Publication Number WO 2008/121342, filed March 28, 2008, entitled "Emulsions and Techniques for Formation," by Chu et al. ; International Patent Publication Number WO 2010/104604, filed March 12, 2010, entitled "Method for the Controlled Creation of Emulsions, Including Multiple Emulsions," by Weitz et al. ; International Patent Publication Number WO 2011/028760, filed September 1, 2010, entitled "Multiple Emulsions Created Using Junctions," by Weitz et al. ; International Patent Publication Number WO 2011/028764, filed September 1, 2010, entitled "Multiple Emulsions Created Using Jetting and Other Techniques," by Weitz et al. ; and International Patent Application Serial Number PCT/US2012/045481 , filed July 5, 2012, entitled "Multiple Emulsions and Techniques for the Formation of Multiple Emulsions," by Shin-Hyun Kim et al., each incorporated herein by reference in its entirety.

Various embodiments of the present invention are generally directed to microfluidic devices for forming multiple emulsion droplets, but not necessarily limited to only uses relevant to making particles or oil absorption. Thus, it should be understood that this is broadly applicable to a range of applications and results, not just particle formation. For example, such multiple emulsions may find use in other applications such as food, beverage, health and beauty aids, paints and coatings, and drugs and drug delivery. For instance, a precise quantity of a drug, pharmaceutical, or other agent can be contained within a multiple emulsion droplet. In some instances, cells can be contained within a multiple emulsion droplet. Other species that can be contained within a multiple emulsion droplet include, for example, biochemical species such as nucleic acids such as siRNA, RNAi and DNA, proteins, peptides, or enzymes. Additional species that can be incorporated within a multiple emulsion droplet of the invention include, but are not limited to, nanoparticles, quantum dots, fragrances, proteins, indicators, dyes, fluorescent species, chemicals, or the like. A multiple emulsion can also serve as a reaction vessel in certain cases, such as for controlling chemical reactions, or for in vitro transcription and translation, e.g., for directed evolution technology.

In various embodiments, a microfluidic device of the present invention includes at least a first microfluidic channel having an exit opening and a second, adjacent microfluidic channel having an exit opening. The exit openings can substantially coincide, and in some cases, the first and second microfluidic channels may be joined together, e.g., having an exit opening resembling a Greek letter theta (Θ) or a number 8. However, in various embodiments, the first and second microfluidic channels may not necessarily be joined together. In addition, in certain cases, more than two such channels are present. For example, there may be three, four, or more such channels.

In some cases, the exit openings may exit into the entrance opening of a third microfluidic channel. The exit openings may actually open within the third microfluidic channel, or in front of the entrance opening to the third microfluidic channel, depending on the application. In some cases, the exit openings are substantially aligned and opposed, or coaxial with, the third microfluidic channel, although this is not a

requirement. The channels can also be contained within a larger channel, e.g., a continuous channel.

If more than one channel is present within the microfluidic device, the different channels used within the same device can be made of similar or different materials. For example, some or all of the channels within a specific device may be glass capillaries, or some or all of the channels within a device may be formed of a polymer, for example, polydimethylsiloxane, as discussed below. In addition, in some embodiments, one or more of the channels may be constricted or tapered at an entrance or exit opening, which can provide geometries that aid in producing consistent multiple emulsions. Further details of preparing microfluidic devices are discussed in detail below.

Each of the first and second microfluidic channels can release a first fluid and a second fluid, respectively, into a continuous fluid, e.g., one that is flowing into the third microfluidic channel, e.g., from the continuous channel. The continuous fluid may be, in some cases, water or another aqueous fluid. If the first fluid, the second fluid, and the continuous fluid are each substantially immiscible, then a droplet may be created within the third microfluidic channel containing each of the first fluid and the second fluid. Depending on the amounts and flow rates of the first fluid and the second fluid, a droplet may be formed where the first fluid and the second fluid are equally, or unequally, divided within the droplet. For example, the weight ratio of the first fluid to the second fluid can be about 10: 1, 8: 1, 5: 1, 4: 1, 3: 1, 2: 1, 1: 1, 1:2, 1:3, 1:4, 1:5, 1:8, or 1: 10, or the weight ratio of the first fluid to the second fluid can be between about 0.1 and about 10, between about 0.2 and about 5, between about 0.5 and about 2, between about 0.5 and about 1.5, between about 0.8 and about 1.2, or between about 0.9 and about 1.1.

In various embodiments, the first fluid and the second fluid may form a Janus configuration, where each of the first fluid and the second fluid contacts the continuous fluid. One example of a Janus droplet is shown exiting exit openings 53 and 54 as droplet 69 in FIG. IB. In some cases, such a configuration may be stable, or the fluids may be solidified, e.g., via polymerization, into a Janus particle configuration. Non- limiting examples of techniques for polymerization and other solidification techniques are discussed herein. Thus, in accordance with certain embodiments, droplets or particles having such a Janus configuration may be readily prepared using such microfluidic devices.

In some embodiments, a Janus configuration of a first fluid and a second fluid is relatively unstable, e.g., if the surface energy between the first fluid and the continuous fluid, and the second fluid and the continuous fluid, are substantially different. In some cases, the fluids may seek to lower their surface energy, and one fluid or the other may preferentially stay in contact with the continuous fluid while the other fluid minimizes (or eliminates) such contact. Thus, such a Janus configuration of fluids, if no steps are taken to stop this process (such as polymerization or solidification of the fluids), may eventually form a different configuration where the first fluid is at least partially surrounded by the second fluid (or vice versa). For instance, at least about 50%, at least about 75%, at least about 90%, at least about 95%, or at least about 99% of the outer surface of the droplet (by area) may be the second fluid. In such a configuration, the first fluid may have little or no contact with the continuous fluid surrounding the droplet. See, e.g., FIG. IB.

In some embodiments, the first fluid, the second fluid, and the continuous fluid are each essentially immiscible, at least on the time scale of forming droplets. As mentioned, it is not a requirement that the droplets are solidified to form particles; in various embodiments or applications, the present invention is generally directed simply to the formation of multiple emulsion droplets. A non-limiting example of a system involving three essentially mutually immiscible fluids is a silicone oil, a mineral oil, and an aqueous solution (i.e., water, or water containing one or more other species that are dissolved and/or suspended therein, for example, a salt solution, a saline solution, a suspension of water containing particles or cells, or the like). Another example of a system is a silicone oil, a fluorocarbon oil, and an aqueous solution. Yet another example of a system is a hydrocarbon oil (e.g., hexadecane), a fluorocarbon oil, and an aqueous solution. Non-limiting examples of suitable fluorocarbon oils include

HFE7500, octadecafluorodecahydronaphthalene :

or 1-(1,2,2,3, 3,4,4,5, 5,6, 6-undecafluorocyclohexyl)ethanol:

However, as mentioned, in various embodiments, one or more of the fluids may be solidified or polymerized to form a particle. For example, in various embodiments, the droplets can be solidified or polymerized while the fluids are in a Janus

configuration. In various embodiments, the fluids may form a different configuration (e.g., where a first fluid is partially or completely surrounded by a second fluid), prior to being solidified or polymerized to form particles. In addition, in some cases, only one of the fluids is solidified or polymerized. For instance, if the second fluid surrounds the first fluid and only the second fluid is polymerized, then a core-shell particle having a solid shell and a fluid core can be created.

In various embodiments, one or more of the fluids comprises a monomer that polymerizes on exposure to ultraviolet light. Non-limiting examples of such polymers includes polyacrylates and other polymers such as those described herein. Other methods may also be used in addition to or instead of ultraviolet polymerization. For instance, a fluid may be dried, gelled, and/or polymerized, and/or otherwise solidified, e.g., to form a solid, or at least a semi-solid. The solid that is formed may be rigid in some embodiments, although in other cases, the solid may be elastic, rubbery, deformable, etc. For example, in various embodiments, a fluid can be cooled to a temperature below the melting point or glass transition temperature of the fluid to cause solidification, a chemical reaction may be induced that causes at least a portion of the fluid to solidify (for example, a polymerization reaction, a reaction between two fluids that produces a solid product, etc.), or the like. Other examples include pH-responsive or molecular-recognizable polymers, e.g., materials that gel upon exposure to a certain pH, or to a certain species. In addition, in some embodiments, more than one of these techniques and/or other techniques can be used.

In various embodiments, one or more of the fluids contains a porogen, i.e., a species that is removed after solidification or polymerization of the droplet to form a particle. The porogen can be partially or completely removed from the particle, leaving behind a void or pore within the particle. In some cases, depending on the amount or distribution of porogen present within the droplet, fairly large void volumes can be created within the particle through removal of the porogen, for example, voids of at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, or at least about 50% of the volume of the particle. One or more porogens may be used during particle formation. In some cases, the porogen is relatively inert, e.g., to the fluids forming the droplets, and/or to ultraviolet radiation and/or other techniques that may be used for solidification or polymerization. After solidification or polymerization, the porogen may be used with any suitable technique. Thus, in various embodiments, the porogen may comprise

polydimethylsiloxane, which can remain in a fluid state and is not polymerized through exposure to ultraviolet radiation, but can be at least partially removed (e.g., extracted or dissolved) from a particle using exposure to an organic fluid such as isopropanol. In various embodiments, the porogen may comprise ionic salt crystals (e.g., NaCl, KC1, etc.), which are not readily soluble in organic fluids, but can be removed or dissolved via exposure of the particles to water or other aqueous fluids. In various embodiments, the porogen may comprise ice, which can be subsequently readily removed via appropriate changes in temperature.

In some cases, a porogen can be used that can concentrate, and in some embodiments, to such a degree that the porogen begins to form an essentially continuous phase within the droplet. This may be created, for example, by the use of a porogen that is able to substantially concentrate within the first section, e.g., due to immiscibility, density-driven processes, stochastic-driven processes, a chemical reaction, or other suitable effects. In some cases, the porogen is allowed to concentrate such that a separate phase is formed, i.e., a complete phase separation occurs between the porogen and the fluid containing the porogen. This may be desired in some embodiments, e.g., to create a hollow particle. However, in various embodiments, phase separation may be stopped or arrested prior to complete phase separation. For example, the droplets can be exposed to ultraviolet light or appropriate changes in temperatures to slow or stop this process.

In various embodiments, the process may be stopped such that the particle contains a first section having a relatively high concentration of porogen, and a second section having a relatively low concentration of porogen. In some cases, as mentioned, the first section forms an essentially continuous phase, optionally containing discrete portions of a fluid (e.g., in the case of an incomplete phase separation).

The porogen may also be removed such that void volumes or pores are created in the particle that generally reflects the distribution of porogen within the particle when the droplet was solidified or polymerized to from the particle. This may be particularly useful in applications, for example, where a certain configuration of pores is desired. In addition, in certain embodiments, there can be some amounts of residual polymer or other material still present within the void volumes or pores, e.g., caused by trapped, discrete portions of fluid that were not removed when the surrounding porogen was removed.

Any amount or weight ratio of porogen can be used. For example, the weight ratio between the porogen and the monomer or fluid containing the porogen may be between about 10: 1 and about 1: 10, between about 5: 1 and about 1:5, between about 3: 1 and about 1:3, or between about 2: 1 and about 1:2. In addition, in certain instances, the weight ratio may be about 10: 1, 8: 1, 5: 1, 4: 1, 3: 1, 2: 1, 1: 1, 1:2, 1:3, 1:4, 1:5, 1:8, or 1: 10.

In some cases, the particles are produced at relatively high rates. The rate of production of particles may be determined by the droplet formation frequency, which under various conditions can vary between approximately 1 Hz and 5000 Hz. In some cases, the rate of droplet production may be at least about 1 Hz, at least about 10 Hz, at least about 100 Hz, at least about 200 Hz, at least about 300 Hz, at least about 500 Hz, at least about 750 Hz, at least about 1,000 Hz, at least about 2,000 Hz, at least about 3,000 Hz, at least about 4,000 Hz, or at least about 5,000 Hz.

In aspects of the present invention, as discussed, particles are formed by flowing fluids through one or more conduits or channels. The system may be a microfluidic system. "Microfluidic," as used herein, refers to a device, apparatus, and/or system including at least one fluid channel having a cross-sectional dimension of less than about 1 millimeter ("mm"), and in some cases, a ratio of length to largest cross- sectional dimension of at least 3: 1. One or more conduits of the system may be a capillary tube. In some cases, multiple channels are provided, and in some embodiments, at least some are nested, as described herein. The channels may be in the microfluidic size range and may have, for example, average inner diameters, or portions having an inner diameter, of less than about 1 millimeter, less than about 300 micrometers, less than about 100 micrometers, less than about 30 micrometers, less than about 10 micrometers, less than about 3 micrometers, or less than about 1 micrometer, thereby providing droplets having comparable average diameters. One or more of the channels may (but not necessarily), in cross-section, have a height that is substantially the same as a width at the same point. A channel may include an opening that may be smaller, larger, or the same size as the average diameter of the channel. For example, channel openings may have diameters of less than about 1 mm, less than about 500 micrometers, less than about 300 micrometers, less than about 200 micrometers, less than about 100 micrometers, less than about 50 micrometers, less than about 30 micrometers, less than about 20 micrometers, less than about 10 micrometers, less than about 3 micrometers, etc. In cross-section, the channels may be rectangular or substantially non-rectangular, such as circular or elliptical. The channels of various embodiments of the present invention may also be disposed in or nested in another channel, and multiple nestings are possible in some cases. In some embodiments, one channel may be concentrically retained in another channel, and the two channels are considered to be concentric. However, one concentric channel may be positioned off-center with respect to another, surrounding channel, i.e., "concentric" does not necessarily refer to tubes that are strictly coaxial. By using a concentric or nesting geometry, two fluids that are miscible may avoid contact.

As mentioned, a variety of materials and methods, according to certain aspects of the invention, may be used to form systems, including microfluidic systems, that can be configured to produce the droplets or particles described herein. In some cases, the various materials selected lend themselves to various methods. For example, various components of the invention are configured from solid materials, in which the conduits are configured via micromachining, film deposition processes such as spin coating and chemical vapor deposition, laser fabrication, photolithographic techniques, etching methods including wet chemical or plasma processes, and the like. See, for example, Scientific American, 248:44-55, 1983 (Angell, et ah). In various embodiments, at least a portion of the fluidic system is formed of silicon by etching features in a silicon chip. Technologies for precise and efficient fabrication of various fluidic systems and devices of various embodiments of the invention from silicon are known. Various components of the systems and devices of various embodiments of the invention are configured of a polymer, for example, an elastomeric polymer such as polydimethylsiloxane ("PDMS"), polytetrafluoroethylene ("PTFE" or Teflon^®), or the like.

Different components can be fabricated of different materials. For example, a base portion including a bottom wall and side walls can be fabricated from an opaque material such as silicon or PDMS, and a top portion can be fabricated from a transparent or at least partially transparent material, such as glass or a transparent polymer, for observation and/or control of the fluidic process. Components can be coated so as to expose a desired chemical functionality to fluids that contact interior conduit walls, where the base supporting material does not have a precise, desired functionality. For example, components can be fabricated as illustrated, with interior conduit walls coated with another material. Materials used to fabricate various components of the systems and devices of the invention, e.g., materials used to coat interior walls of fluid conduits, may desirably be selected from among those materials that will not adversely affect or be affected by fluid flowing through the fluidic system, e.g., a material or materials that are chemically inert in the presence of fluids to be used within the device. A non-limiting example of such a coating is disclosed below; additional examples are disclosed in Int. Pat. Apl. Ser. No. PCT/US2009/000850, filed February 11, 2009, entitled "Surfaces, Including Microfluidic Channels, With Controlled Wetting Properties," by Weitz et al., published as WO 2009/120254 on October 1, 2009, incorporated herein by reference.

Various components of various embodiments of the invention are fabricated from polymeric and/or flexible and/or elastomeric materials, and may be conveniently formed of a hardenable fluid, facilitating fabrication via molding (e.g. replica molding, injection molding, cast molding, rotational molding, etc.). The hardenable fluid may be essentially any fluid that can be induced to solidify, or that spontaneously solidifies, into a solid capable of containing and/or transporting fluids contemplated for use in and with the fluidic network. In some embodiments, the hardenable fluid comprises a polymeric liquid or a liquid polymeric precursor (i.e., a "prepolymer"). Suitable polymeric liquids include, for example, thermoplastic polymers, thermoset polymers, or mixture of such polymers heated above their melting point. As another example, a suitable polymeric liquid may include a solution of one or more polymers in a suitable solvent, which solution forms a solid polymeric material upon removal of the solvent, for example, by evaporation. Such polymeric materials, which can be solidified from, for example, a melt state or by solvent evaporation, are well known to those of ordinary skill in the art. A variety of polymeric materials, many of which are elastomeric, are also suitable for forming molds or mold masters, for embodiments where one or both of the mold masters is composed of an elastomeric material. A non-limiting list of examples of such polymers includes polymers of the general classes of silicone polymers, epoxy polymers, and acrylate polymers. Epoxy polymers are characterized by the presence of a three- membered cyclic ether group commonly referred to as an epoxy group, 1,2-epoxide, or oxirane. For example, diglycidyl ethers of bisphenol A can be used, in addition to compounds based on aromatic amine, triazine, and cycloaliphatic backbones. Another example includes the well-known Novolac polymers. Non-limiting examples of silicone elastomers suitable for use according to various embodiments of the invention include those formed from precursors, including the chlorosilanes such as methylchlorosilanes, ethylchlorosilanes, phenylchlorosilanes, etc.

Silicone polymers are utilized in some embodiments, for example, the silicone elastomer polydimethylsiloxane. Non-limiting examples of PDMS polymers include those sold under the trademark Sylgard by Dow Chemical Co., Midland, MI, such as Sylgard 182, Sylgard 184, and Sylgard 186. Silicone polymers including PDMS have several beneficial properties simplifying fabrication of the microfluidic structures of the invention. For instance, such materials are inexpensive, readily available, and can be solidified from a prepolymeric liquid via curing with heat. For example, PDMSs are typically curable by exposure of the prepolymeric liquid to temperatures of, for example, about 65 °C to about 75 °C for exposure times of, for example, about an hour. Also, silicone polymers, such as PDMS, can be elastomeric, and thus may be useful for forming very small features with relatively high aspect ratios, necessary in certain embodiments of the invention. Flexible (e.g., elastomeric) molds or masters can be advantageous in this regard.

An advantage of forming structures such as microfluidic structures of the invention from silicone polymers, such as PDMS, is the ability of such polymers to be oxidized, for example by exposure to an oxygen-containing plasma, such as an air plasma, so that the oxidized structures contain, at their surface, chemical groups capable of cross-linking to other oxidized silicone polymer surfaces or to the oxidized surfaces of a variety of other polymeric and non-polymeric materials. Thus, components can be fabricated and then oxidized and essentially irreversibly sealed to other silicone polymer surfaces, or to the surfaces of other substrates reactive with the oxidized silicone polymer surfaces, without the need for separate adhesives or other sealing means. In some cases, sealing can be completed simply by contacting an oxidized silicone surface to another surface without the need to apply auxiliary pressure to form the seal. That is, the pre- oxidized silicone surface acts as a contact adhesive against suitable mating surfaces. Specifically, in addition to being irreversibly sealable to itself, oxidized silicone, such as oxidized PDMS, can also be sealed irreversibly to a range of oxidized materials other than itself including, for example, glass, silicon, silicon oxide, quartz, silicon nitride, polyethylene, polystyrene, glassy carbon, and epoxy polymers, which have been oxidized in a similar fashion to the PDMS surface (for example, via exposure to an oxygen-containing plasma). Oxidation and sealing methods useful in the context of various embodiments of the present invention, as well as overall molding techniques, are described in the art, for example, in an article entitled "Rapid Prototyping of

Microfluidic Systems and Polydimethylsiloxane," Anal. Chem., 70:474-480, 1998 (Duffy et ah), incorporated herein by reference.

In some embodiments, certain microfluidic structures of the invention (or interior, fluid-contacting surfaces) may be formed from certain oxidized silicone polymers. Such surfaces may be more hydrophilic than the surface of an elastomeric polymer. Such hydrophilic conduit surfaces can thus be more easily filled and wetted with aqueous solutions.

A bottom wall of a microfluidic device of various embodiments of the invention is formed of a material different from one or more side walls or a top wall, or other components. For example, in some embodiments, the interior surface of a bottom wall comprises the surface of a silicon wafer or microchip, or other substrate. Other components may, as described above, be sealed to such alternative substrates. Where it is desired to seal a component comprising a silicone polymer (e.g., PDMS) to a substrate (e.g., bottom wall) of different material, the substrate may be selected from the group of materials to which oxidized silicone polymer is able to irreversibly seal (e.g., glass, silicon, silicon oxide, quartz, silicon nitride, polyethylene, polystyrene, epoxy polymers, and glassy carbon surfaces, which have been oxidized). Alternatively, other sealing techniques may be used, as would be apparent to those of ordinary skill in the art, including, but not limited to, the use of separate adhesives, bonding, solvent bonding, ultrasonic welding, etc.

Production of large quantities of particles may be facilitated by the parallel use of multiple devices such as those described herein, in some embodiments. In some cases, relatively large numbers of devices may be used in parallel, for example at least about 10 devices, at least about 30 devices, at least about 50 devices, at least about 75 devices, at least about 100 devices, at least about 200 devices, at least about 300 devices, at least about 500 devices, at least about 750 devices, or at least about 1,000 devices or more may be operated in parallel. The devices may comprise different conduits (e.g., concentric conduits), openings, microfluidics, etc. In some cases, an array of such devices is formed by stacking the devices horizontally and/or vertically. The devices may be commonly controlled, or separately controlled, and may be provided with common or separate sources of various fluids, depending on the application.

The following documents are incorporated herein by reference in their entirety for all purposes: International Patent Publication Number WO 2004/091763, filed April 9, 2004, entitled "Formation and Control of Fluidic Species," by Link et al. ; International Patent Publication Number WO 2004/002627, filed June 3, 2003, entitled "Method and Apparatus for Fluid Dispersion," by Stone et al. ; International Patent Publication

Number WO 2006/096571, filed March 3, 2006, entitled "Method and Apparatus for Forming Multiple Emulsions," by Weitz et al. ; International Patent Publication Number WO 2005/021151, filed August 27, 2004, entitled "Electronic Control of Fluidic

Species," by Link et al. ; International Patent Publication Number WO 2008/121342, filed March 28, 2008, entitled "Emulsions and Techniques for Formation," by Chu et al. ; International Patent Publication Number WO 2010/104604, filed March 12, 2010, entitled "Method for the Controlled Creation of Emulsions, Including Multiple

Emulsions," by Weitz et al. ; International Patent Publication Number WO 2011/028760, filed September 1, 2010, entitled "Multiple Emulsions Created Using Junctions," by Weitz et al; International Patent Publication Number WO 2011/028764, filed September 1, 2010, entitled "Multiple Emulsions Created Using Jetting and Other Techniques," by Weitz et al.; U.S. Provisional Patent Application Serial No. 61/504,990, filed on July 6, 2011, entitled "Multiple Emulsions and Techniques for the Formation of Multiple Emulsions," by Kim et al. ; International Patent Application Serial Number

PCT/US2012/045481, filed July 5, 2012, entitled "Multiple Emulsions and Techniques for the Formation of Multiple Emulsions," by Kim et al. ; and U.S. Provisional Patent Application Serial Number 61/505,001 , filed July 6, 2011 , entitled "Delivery to

Hydrocarbons or Oil, Including Crude Oil," by Abbaspourrad et al. Also incorporated herein by reference in their entireties are U.S. Provisional Patent Application Serial No. 61/728,478, filed November 20, 2012, entitled "Particles for Uptake or Sensing Oil and Other Applications, and Related Methods"; and U.S. Provisional Patent Application Serial No. 61/730,026, filed November 26, 2012, entitled "Particles for Uptake or Sensing Oil and Other Applications, and Related Methods."

The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

EXAMPLE 1

This example illustrates smart microcapsules for uptake and sensing oil, in accordance with certain embodiments of the invention. In this example, microfluidic techniques were used to fabricate oil sensing particles, which can uptake and carry oil. A single emulsion template was used in a glass microcapiUary device to form particles with a porous hydrophobic core and hydrophilic shell structure. The control gained from the microfluidic platform can be used to govern the size of the particles as well as relative size of the core to the shell. These polymer particles were designed to uptake different types of oil such as aromatic and aliphatic oils. In this strategy, by controlling the type of the monomer and surfactant and controlling the spreading factor, various core shell particle can be designed using a single emulsion strategy.

Surface properties of these particles were tuned and modified using different types of colloidal hydrophilic particles, such as hydrophilic silica particles. The concentration of the colloidal particles, which were anchored at the interface, can be used to tune the surface properties of the shell. The core shell structure of the oil sensing particles was determined by factors, such as the interfacial tension and the spreading factor. When these particles were dispersed in an aquous fluid saturated with oil, or when the particles had direct contact with oil droplets, the particles began to uptake the oil. This process depended on various factors, such as the type of the oil and the size of the hydrophobic core of particles. For example, the oil uptake may take between about 1 hour up to a few days, and after specific amounts of time, the particles can become saturated and the hydrophobic porous core filled with oil molecules.

In addition, after an oil uptake process, the particles may be recovered, and the adsorbed oil extracted and measured from the particles. In addition, the brightness of the core, calibrated using imaging software, may also be used to determine the amount of adsorbed oil.

A schematic of a process of particle fabrication is shown in FIG. 2. A theta (Θ) shaped glass capillary was used to produce core shell particles. After production, the particles were cured using UV light. In FIG. 3A, the mechanism of the generation of core-shell particles with a porous hydrophobic core is shown. After generation of the droplet, two steps of macro and microphase separation were performed, and after UV exposure, the template was washed out from the core to generate a porous structure.

In FIGS. 3B-3E, four different regions of the particle are shown using SEM micrographs, and correlated with a schematic diagram of a particle as is shown in FIG. 3F. FIG. 3B shows the surface structure of the particle, while FIG. 3C shows the boundary between two hydrophobic and hydrophilic regions in the particle. A portion of the boundary is identified with the dashed line in Fig. 3C, separating different structural regions within the particle. FIGS. 3D and 3E represent two different porosities inside the particle, which was related to the microphase separation during UV polymerization process. The locations of these SEMs within the particle are identified by arrows to the schematic diagram of the particle in FIG. 3F.

EXAMPLE 2

This example describes a technique to achieve water dispersion of particles having a hydrophobic nature, by tailoring the particle surface chemistry. For example, such core-shell particles may be constructed with a hydrophobic porous oil-absorbing core and a hydrophilic surface to facilitate dispersal in water. Particles that absorb oil while remaining dispersed in water may be useful for applications in enhanced oil recovery. For example, they may be used as oil sensing probes by injection into, and retrieval from, reservoir locations to determine the presence of oil. Additionally, such particles may function as oil collection vehicles for enhanced oil recovery, such as in less-accessible reservoir locations.

This example illustrates porous core-shell particles designed to sense and uptake oil. Microfluidic and porogen templating techniques were used to fabricate particles with a hydrophobic porous core and a hydrophilic surface. The hydrophilic surface allowed the particles to be dispersed in water, while the hydrophobic core absorbed oil molecules from the surrounding environment. A capillary microfluidic device was used to prepare paired droplets comprising two photocurable monomer mixtures dispersed in an aqueous continuous phase. To lower interfacial energy, the less hydrophobic monomer mixture spontaneously spread and engulfed the more hydrophobic mixture to form a core-shell droplet. The monomer mixture, which spread to form the shell, contained hydrophilic silica nanoparticles; the nanoparticles adsorbed at the aqueous interface and conferred hydrophilicity to the particle surface for dispersion in water. The inner mixture was a binary blend of a photocurable monomer and a porogen PDMS template. The porous particles were formed by photopolymerizing the monomers and subsequently removing the template porogen. Unlike hydrophobic oil-absorbing particles which are unstable in aqueous solutions, these surface-modified particles absorbed oil from the environment while remaining well dispersed in water.

Core-shell droplets: Two different monomer mixtures were emulsified into single drops in an aqueous continuous phase using a glass capillary microfluidic device. The device was constructed from a theta (Θ) shaped injection capillary, which had two separate channels. The theta shaped capillary was tapered and inserted inside a cylindrical collection capillary to increase the velocity of the continuous phase by confining the flow near the tip of the injection capillary. Both theta shaped and cylindrical capillaries were placed coaxially inside a square capillary whose inner dimension was the same as that of the outer diameter of the theta shaped and cylindrical capillaries; a schematic of the device is shown in FIG. 2A.

A monomer of ethoxylated trimethylolpropane triacrylate ("ETPTA") containing dispersed silica nanoparticles was flowed through one channel of the theta- shaped capillary and isobornylmethaacrylate ("IBMA") plus PDMS oil and a crosslinker (e.g., hexandiol dimethylacrylate) was flowed through the second channel, as shown in FIG. 2B. In this example, the IBMA, the PDMS, and the crosslinker are referred to as the

IBMA mixture. The continuous phase was introduced by pumping an aqueous surfactant solution of 1 wt ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (e.g., commercially available Pluronic F-108) through the interstices of the square and cylindrical capillaries.

Droplets were generated with the two different monomer mixtures; the upper phase was ETPTA with dispersed silica particles while the lower phase was the IBMA mixture, as shown in FIGS. 2A-2C. Fig. 2A shows the EPTA-S1O₂ and an initiator flowing in the upper portion of a theta-shaped injection capillary, while IBMA, PDMS, and initiator flow through the lower portion of the capillary. The exit of the injection capillary is positioned near a collection capillary, and the continuous phase flowing outside of the injection capillary flows into the collection capillary. At this junction, the fluids from the upper and lower portions of the injection capillary come into contact with each other to form droplets, which are contained within the continuous phase comprising Pluronic F-108. Fig. 2B shows an image of such an arrangement in operation, while Fig. 2C shows particles that are subsequently formed after exposing the droplets to UV light.

The ETPTA phase completely wetted the surface of the IBMA mixture, forming a non-concentric core-shell droplet as shown in FIG. 2A. The complete coverage is believed to occur because the spreading of ETPTA reduces the interfacial area of high surface tension between the IBMA mixture and water. The ETPTA phase contained hydrophilic silica particles, which spontaneously adsorbed to the interface with water, where they minimized the total interfacial energy by reducing the contact area between the ETPTA and the water. The particles remain trapped at the ETPT A/water interface because the reduction of interfacial energy was much greater than thermal energy.

Following droplet generation, the ETPTA spread on the surface and mixed with the IBMA and PDMS in the core. Due to the low miscibility of the ETPTA and PDMS, a mixture-driven phase separation occurred within the droplet; thus, the PDMS phase separated from the mixture, resulting in formation of a PDMS-rich inner layer and monomer-rich middle layer, as is shown in Fig. 3A. Both layers comprised a binary blend of photocurable monomers and porogen PDMS. The PDMS-rich inner layer is distinguished by a much larger ratio of porogen PDMS to monomer in comparison with the middle layer. The outermost layer of the drop was comprised of silica nanoparticles dispersed within the monomer mixture. A diagram illustrating the droplet layers is shown in the first step of FIG. 3A. The porous particles were prepared by in situ photopolymerization of the multi-layered droplets containing porogen PDMS. The droplets are initially formed as previously discussed with respect to FIG. 2, including an upper half containing ETPTA and silica particles, and a lower half containing IBMA and PDMS. The difference in the porogen to monomer ratio within the monomer-rich and PDMS-rich layers resulted in the formation of dissimilar polymeric structures within each layer. In the PDMS-rich layer, the precipitation polymerization of monomers resulted in inter-connected polymeric particles whose sub-micron interstices are filled with PDMS. By contrast, polymerization in the monomer-rich middle layer lead to the exclusion of PDMS to sub- 100 nm domains dispersed within a continuous polymeric matrix. Polymerized regions were shown as a lighter color while darker colors represent the porogen PDMS in the second and third steps of FIG. 3A.

To replace liquid PDMS with air, the particles were washed with isopropanol ("IP A") and subsequently dried. Air-filled pores are represented with a white color in the last step shown in FIG. 3A, where the porogen (PDMS) was removed, resulting in pores filled with air.

The prepared multilayered particles were cut in half and SEM images obtained in order to examine the surface and internal structure, as is shown in FIGS. 3B-3E. At the surface, anchored silica particles formed hexagonal arrays over the entire exterior of the microparticle, as shown in the SEM image in FIG. 3B. A high magnification SEM image of the protruding silica particles, about 380 nm in diameter, is shown in the inset of FIG. 3B. The outer layer was characterized by a polymer matrix enriched with dispersed hydrophilic silica particles as shown in FIG. 3C. Functionalization with colloidal silica confers surface hydrophilicity to the particles, which facilitated dispersal in water. By contrast, the porous structure of the hydrophobic middle and inner layers was designed to absorb oil. The middle layer was characterized by small pores of sub- 100 nm size, as shown in FIG. 3D. The inner layer was comprised of interconnected

IBMA spheres characterized by larger pores of sub-micron size, as shown in FIG. 3E. A high magnification SEM image of the porous inner layer is shown in the inset of FIG. 3E.

The multilayered droplets, which act as templates for the porous particles, likely formed by phase separation of the ETPTA, IBMA, and PDMS mixture. To test this hypothesis, bulk mixtures of these three fluids were used to determine their ternary phase diagram; the phase boundary is shown by the dashed line within the phase diagram in FIG. 4. For small concentrations of ETPTA and PDMS, the fluids mixed

homogeneously, as indicated by the circles in FIG. 4. In stark contrast, for sufficiently large ETPTA and PDMS concentrations, the fluids did not mix homogeneously; instead, they phase-separated into PDMS-rich and monomer-rich phases, as indicated by the diamonds in FIG. 4. To form multilayered droplets that act as templates for the porous particles, the droplet fluid composition was selected to fall within the two-phase region; this was achieved by adjusting the relative flow rates of the ETPTA and IBMA/PDMS mixture. In this case, a phase separation initiated within the droplets, and formed PDMS-rich and monomer-rich layers; eventually, phase separation would have completed, resulting in a multi-layered equilibrium structure. During the transition to an equilibrium structure, the porogen to monomer ratio within the layers changed with time. Therefore, the time interval between droplet generation and UV exposure was important to control; it was used to determine the final porogen to monomer ratio at the time of polymerization, and thus the corresponding polymeric micro structure. In this example, phase separation was arrested a few seconds after droplet generation by in situ photopolymerization to obtain the desired microstructures; thus, adjusting the interval between droplet generation and UV exposure provided an additional level of design control for this class of porous particles.

To approximate the porogen to monomer ratio, and thus the porosity, within the inner layer at the time of in situ photopolymerization, various combinations of monomer and porogen were prepared in bulk. The mixtures were photopolymerized, and the porogen PDMS was subsequently removed. The resultant porous structures were examined within the bulk polymeric matrix using SEM. The pores within the polymer matrix were found to have become larger in size as the porogen to monomer ratio increases, as shown by the SEM images in FIGS. 8A-8D, which show polymer matrixes formed using different ratios of monomer to porogen (i.e., IBMA:PDMS), as indicated in each figure. FIGS. 8E and 8F show the polymer structure inside polymeric matrixes formed using a ratio of monomer to porogen of 1: 1. By comparing the structures formed in bulk with that of the microparticles, the ratio of porogen to monomer within the inner layer at the time of in situ polymerization was estimated as 1 : 1 and therefore, the porosity was estimated as 50% by volume. Using this approach, the porogen to monomer ratio and the corresponding particle porosity can, in principle, be controlled by adjusting mixture composition and time interval between droplet generation and UV exposure.

Despite its applicability to design porous structures by controlling the extent of phase separation, this technique has a relatively short time intervals between droplet generation and UV irradiation. In the case of longer time intervals, phase separation proceeds to completion and, due to the low monomer content within the PDMS-rich inner layer, no consolidated structure was formed within the inner layer upon UV exposure. To verify this observation, droplets were generated and stored for 12 hours before photopolymerization. Following washing steps, the particles were imaged using SEM. An approximately 45 micrometer diameter cavity was observed at the particle surface as shown in FIG. 9A; a higher magnification SEM image is shown in FIG. 9B. This result illustrates the effect of the time interval between droplet generation and photopolymerization in fabricating particles with controlled micro structure using this technique.

The size of the porous inner layer may be controlled by varying the relative volumetric flow rates of the ETPTA (Qj) and IBMA/PDMS (Q₂) mixtures. Operating in the dripping mode, the size of the inner layer was adjusted with three different relative flow rates of Q₁/Q₂ = 0.6, Q₁/Q₂ = 1, and Q₁/Q₂ = 1.5, while maintaining a constant sum of Qi and Q₂. Optical microscope images of the resultant microparticles are shown in FIGS. 5A, 5B, 5D, 5E, 5G, and 5H at various times. In the optical images, a distinct dark sphere was observed inside the particle, which is the porous inner layer; this high opacity was caused by strong light scattering in the heterogeneous inner layer structure. Using SEM imaging (see FIGS. 5C, 5F, and 51), the size of the inner core region was observed to increase with increasing ratios of Qi/Q₂- Adjusting the relative flow rates thus offers a simple and effective way of controlling the size of the oil-absorbing porous inner layer.

To demonstrate the effectiveness of porous particles to absorb oil, the particles were immersed in an aqueous solution saturated with oil, and the amount of oil absorbed was subsequently measured. The dried porous particles (Q₁/Q₂ = 0.6) were placed within a glass vial and a paper filter set on top of the particles to prevent them from rising. To prepare an aqueous solution saturated with oil, a water layer was added to the bottom of the vial followed by gentle addition of an oil layer on top of the water surface. After sealing the vial, the samples were incubated at about 65 °C for predetermined amounts of time. The particles were dried and subsequently weighed to measure the amount of oil absorbed at different intervals over a 52 hour time period as shown in FIG. 6A. The maximum amount of absorbed oil reached 16 wt of the initial particle sample weight at 48 hours; no significant increase in oil uptake was measured after 48 hours as observed in the plot of FIG. 6A. Remarkably, despite the intrinsic hydrophobic nature of the particles, they remained stable and well dispersed in water throughout the experiment; this was attributed to the excellent dispersion of the particles to the designed hydrophilic surface. This result illustrates the potential of surface-functionalized porous particles as effective oil carriers in aqueous environments.

An alternative method to determine the amount of oil absorbed is to correlate the increasing transparency of the inner layer with the amount of oil absorbed as a function of time. The air-filled pores of water-dispersed particles resulted in an opaqueness of the inner layer as characterized by optical microscopy in transmission mode. Mie scattering dominated because of the high contrast in refractive indices between air (n_air=\) and IBMA particles (ΠΙΒΜΑ= 1.47) within the inner layer. As decane oil molecules

were absorbed, the contrast decreases, resulting in diminished scattering and increased transparency. The particles were imaged using an optical microscope, and the changes in the brightness of the inner layer measured as a function of time using ImageJ software; the brightness was normalized with the maximum intensity. At 48 hours, the pores were saturated with oil and the brightness reached its maximum value, after which no significant changes were observed. The averaged data of brightness as a function of time are shown in FIG. 6B. Microscope images of a particle core increasing in brightness at different time intervals are shown in FIGS. 6C-6J. Interestingly, this data is in accord with the previous weight measurement results. Thus, by implementing this alternate characterization technique, a fast and efficient method for measuring the amount of oil absorbed was demonstrated; this result highlights how these particles may be used in oil sensing applications.

For use in EOR applications, it may be necessary to retrieve the particles after oil uptake. To facilitate their recovery, the particles may be functionalized using iron oxide magnetic nanoparticles. 0.1 wt iron oxide nanoparticles stabilized by oleic acid (commercially available from Sigma- Aldrich) were dispersed in a ETPTA monomer to fabricate magnetic-responsive oil absorbing particles. Upon applying an external magnetic force, the particles responded and translated in the direction of the applied magnetic field.

The versatility of the porous particles was also demonstrated by dispersing them in an oil-in-water emulsion to absorb oil directly from the surface of oil drops. The particles were dispersed in water; these particles were characterized by an opaque core as shown in FIG. 7A. After addition of oil, the vials of samples were shaken to form oil drops suspended in water. The particles assembled at oil-water interfaces and begin to uptake oil as shown in the optical image in FIG. 7B. The particles remained at the interface and did not partition into the oil drops; this is believed due to the designed hydrophilic surfaces of the particles.

Optical microscopy was used to verify the complete coverage of an oil droplet at different focal planes. Interestingly, it was observed that within minutes, small spherical oil droplets become non- spherical, as highlighted by the dashed lines in FIG. 7C. The non-spherical oil droplets are believed to form because of volume depletion due to oil uptake and subsequent particle jamming at the interface. Two different circular lines were observed at the particle surface as shown in FIGS. 7D and 7E. The smaller circle was the inner layer of the particle, whose brightness increased as oil was absorbed, and the larger circle was the contact line of the particle protruding into the oil droplet. It was observed that as the particles absorbed oil, the inner layers transformed from an initially opaque to a bright appearance within minutes as shown in FIG. 7F. It was also observed that the time for oil uptake was faster from an oil drop surface than an aqueous solution containing dissolved oil. It was thus demonstrated that the particles were not limited to oil uptake from aqueous solutions, and the particles can also anchor to oil surfaces and quickly absorb oil in the case of direct contact with oil droplets.

Thus, this example shows that by selective tuning of particle core and surface properties, fabrication of oil-absorbing particles that remain well dispersed in water can be achieved. In addition, this example shows a pragmatic approach to fabricate core- shell particles that absorb oil while remaining well-dispersed in aqueous solutions.

Microfluidics, mixing-induced phase separation, and precipitation polymerization were combined to engineer particles with a hydrophobic porous core and hydrophilic shell. The hydrophobic porous core was designed to uptake oil molecules, while the hydrophilic shell confers dispersion of particles in an aqueous phase. The surface properties of the core-shell particles were tuned by including silica nanoparticles at the particle surface with different degrees of hydrophilicity.

Furthermore, the effectiveness of the particles to absorb oil directly from oil drops was demonstrated. Moreover, the ability of these particles was not limited to direct contact with oil, but can absorb oil molecules from an aqueous solution. The amount of oil absorbed by weight as well as optical measurements may be characterized. By adjusting the size of the core and its porosity, the amount of oil absorbed may be enhanced. The core-shell particles may also be functionalized using iron oxide nanoparticles to facilitate their retrieval after oil absorption. This example thus shows fabrication of functionalized particles that can absorb oil while remaining well dispersed in aqueous solution. These particles may be used, for example, as oil sensors and/or oil recovery vehicles for use in oil remediation or EOR applications. While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary, and that the actual parameters, dimensions, materials, and/or configurations may depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases.

Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B," when used in conjunction with open-ended language such as "comprising" can refer, in an embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e., "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of," when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in an embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as

"comprising," "including," "carrying," "having," "containing," "involving," "holding," "composed of," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and

"consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

What is claimed is:

Claims

A method, comprising:

injecting particles into a field suspected of containing a subterranean oil reservoir, wherein the particles comprise an inner region and a layer of nanoparticles substantially covering the surface of the particle.

The method of claim 1, further comprising recovering at least some of the particles from the field.

The method of claim 2, comprising injecting the particles into the field at a first location, and recovering at least some of the particles from the field at a second location different from the first location.

The method of any one of claims 2 or 3, further comprising determining oil within the recovered particles.

The method of claim 4, wherein at least some of the particles comprise at least 5 wt oil from the subterranean oil reservoir.

The method of any one of claims 2-5, further comprising recovering at least some of the oil from the recovered particles.

The method of any one of claims 2-6, further comprising reusing the recovered particles.

The method of claim 7, wherein reusing the particles comprises removing at least some of the oil from the recovered particles, and injecting the recycled particles into a field suspected of containing a subterranean oil reservoir.

The method of any one of claims 2-7, further comprising recycling the particles. - so lo. The method of any one of claims 1-9, wherein the particle has a maximum

dimension of less than about 1 cm.

11. The method of any one of claims 1-10, wherein the particle has a maximum

dimension of less than about 1 mm.

12. The method of any one of claims 1-11, wherein the particle is substantially

spherical. 13. The method of any one of claims 1-12, wherein the outer region is formed from a material having a water contact angle of less than 90°.

14. The method of any one of claims 1-12, wherein at least some of the nanoparticles are silica nanoparticles.

15. The method of any one of claims 1-14, wherein the nanoparticles have a

maximum dimension of less than about 1 micrometer.

16. The method of any one of claims 1-15, wherein the nanoparticles have a

distribution in diameters such that no more than 5% of the nanoparticles have a diameter greater than about 110% and/or less than about 90% of the overall average cross- sectional diameters of the nanoparticles.

The method of any one of claims 1-16, wherein the particles comprise an outer region having an average pore diameter of between about 100 nm and about 500 nm.

18. The method of claim 17, wherein the average pore diameter is between about 300 nm and about 500 nm.

19. The method of any one of claims 1-18, wherein the inner region comprises at least two polymers.

20. The method of any one of claims 1-19, wherein the inner region is formed from a material having a water contact angle of greater than 90°. 21. The method of any one of claims 1-20, wherein the inner region comprises at least a first portion defined by a first polymer and a second portion defined by a second polymer.

22. The method of claim 21, wherein the weight ratio of the first polymer to the second polymer is between about 0.5 to about 1.5.

23. The method of any one of claims 21 or 22, wherein the first polymer and/or the second polymer is a UV-crosslinkable polymer. 24. The method of any one of claims 21-23, wherein the first portion is surrounded by the second portion.

25. The method of any one of claims 21-24, wherein the second portion comprises a polyacrylate.

The method of any one of claims 21-25, wherein the second portion comprises poly(ethoxylated trimethylolpropane triacrylate).

The method of any one of claims 21-26, wherein the second portion is not symmetrically positioned within the particle.

28. The method of any one of claims 21-27, wherein the first portion has a void volume of at least about 10 vol . 29. The method of any one of claims 21-28, wherein the first portion is not

symmetrically positioned within the particle. The method of any one of claims 21-29, wherein the first polymer comprises a polyacrylate.

The method of any one of claims 21-30, wherein the first polymer comprises poly(isobornylmethaacrylate) .

The method of any one of claims 21-31, wherein the first portion comprises a first section and a second section, the first section having a higher porosity than the second section.

The method of claim 32, wherein the first section is surrounded by the second section.

The method of claim 33, wherein the second section has an average pore diameter of less than about 100 nm.

A method, comprising:

injecting particles into a field suspected of containing a subterranean oil reservoir, wherein the particles comprise an outer region having an average pore diameter of between about 100 nm and about 500 nm, surrounding an inner region.

The method of claim 35, further comprising recovering at least some of the particles from the field.

The method of claim 36, comprising injecting the particles into the field at a first location, and recovering at least some of the particles from the field at a second location different from the first location. 38. The method of any one of claims 36 or 37, further comprising determining oil within the recovered particles.

39. The method of claim 38, wherein at least some of the particles comprise at least 5 wt oil from the subterranean oil reservoir.

40. The method of any one of claims 36-39, further comprising recovering at least some of the oil from the recovered particles.

41. The method of any one of claims 36-40, further comprising reusing the recovered particles. 42. The method of claim 41, wherein reusing the particles comprises removing at least some of the oil from the recovered particles, and injecting the recycled particles into a field suspected of containing a subterranean oil reservoir.

43. The method of any one of claims 36-42, further comprising recycling the

particles.

44. The method of any one of claims 35-43, wherein the particle has a maximum dimension of less than about 1 cm. 45. The method of any one of claims 35-44, wherein the particle has a maximum dimension of less than about 1 mm.

46. The method of any one of claims 35-45, wherein the particle is substantially spherical.

47. The method of any one of claims 35-46, wherein the outer region is formed from a material having a water contact angle of less than 90°.

48. The method of any one of claims 35-47, wherein the outer region comprises nanoparticles. 49 The method of claim 48, wherein the outer region consists essentially of nanoparticles.

50 The method of any one of claims 48 or 49, wherein at least some of the

nanoparticles are silica nanoparticles.

51. The method of any one of claims 48-50, wherein the nanoparticles have a

maximum dimension of less than about 1 micrometer. 52. The method of any one of claims 48-51, wherein the nanoparticles substantially cover the surface of the particle.

53. The method of any one of claims 48-52, wherein the nanoparticles have a

54. The method of any one of claims 35-53, wherein the average pore diameter is between about 300 nm and about 500 nm.

The method of any one of claims 35-54, wherein the inner region comprises at least two polymers.

The method of any one of claims 35-55, wherein the inner region is formed from a material having a water contact angle of greater than 90°.

The method of any one of claims 35-56, wherein the inner region comprises at least a first portion defined by a first polymer and a second portion defined by second polymer.

58. The method of claim 57, wherein the weight ratio of the first polymer to the second polymer is between about 0.5 to about 1.5. The method of any one of claims 57 or 58, wherein the first polymer and/or the second polymer is a UV-crosslinkable polymer.

The method of any one of claims 57-59, wherein the first portion is surrounded by the second portion.

The method of any one of claims 57-60, wherein the second portion comprises a polyacrylate.

The method of any one of claims 57-61, wherein the second portion comprises poly(ethoxylated trimethylolpropane triacrylate).

The method of any one of claims 57-62, wherein the second portion is not symmetrically positioned within the particle.

The method of any one of claims 57-63, wherein the first portion has a void volume of at least about 10 vol . 65. The method of any one of claims 57-64, wherein the first portion is not

symmetrically positioned within the particle.

66. The method of any one of claims 57-65, wherein the first polymer comprises a polyacrylate.

67. The method of any one of claims 57-66, wherein the first polymer comprises poly(isobornylmethaacrylate) .

68. The method of any one of claims 57-67, wherein the first portion comprises a first section and a second section, the first section having a higher porosity than the second section.

69. The method of claim 68, wherein the first section is surrounded by the second section.

70. The method of claim 69, wherein the second section has an average pore diameter of less than about 100 nm.

71. An article, comprising:

a particle comprising an outer region having an average pore diameter of between about 100 nm and about 500 nm, surrounding an inner region

comprising at least 5 wt oil therein, relative to the weight of the particle.

72. The article of claim 71, wherein the inner region comprises at least 10 wt oil therein. 73. The article of any one of claims 71 or 72, wherein the oil comprises a

hydrocarbon oil.

74. The article of any one of claims 71-73, wherein the oil comprises crude oil. 75. The article of any one of claims 71-74, wherein the oil comprises petroleum.

76. The article of any one of claims 71-75, wherein the particle has a maximum

dimension of less than about 1 cm. 77. The article of any one of claims 71-76, wherein the particle has a maximum

dimension of less than about 1 mm.

78. The article of any one of claims 71-77, wherein the particle is substantially

spherical.

79. The article of any one of claims 71-78, wherein the outer region is formed from a material having a water contact angle of less than 90°.

80. The article of any one of claims 71-79, wherein the outer region comprises nanoparticles. 81. The article of claim 80, wherein the outer region consists essentially of

nanoparticles.

82. The article of any one of claims 80 or 81, wherein at least some of the

nanoparticles are silica nanoparticles.

83. The article of any one of claims 80-82, wherein the nanoparticles have a

maximum dimension of less than about 1 micrometer.

84. The article of any one of claims 80-83, wherein the nanoparticles substantially cover the surface of the particle.

85. The article of any one of claims 80-84, wherein the nanoparticles have a

86. The article of any one of claims 71-85, wherein the average pore diameter is between about 300 nm and about 500 nm. 87. The article of any one of claims 71-86, wherein the inner region comprises at least two polymers.

88. The article of any one of claims 71-87, wherein the inner region is formed from a material having a water contact angle of greater than 90°.

89. The article of any one of claims 71-88, wherein the inner region comprises at least a first portion defined by a first polymer and a second portion defined by a second polymer. 90. The article of claim 89, wherein the weight ratio of the first polymer to the

second polymer is between about 0.5 to about 1.5.

91. The article of any one of claims 89 or 90, wherein the first polymer and/or the second polymer is a UV-crosslinkable polymer.

The article of any one of claims 89-91, wherein the first portion is surrounded by the second portion.

The article of any one of claims 89-92, wherein the second portion comprises a polyacrylate.

94. The article of any one of claims 89-93, wherein the second portion comprises poly(ethoxylated trimethylolpropane triacrylate). 95. The article of any one of claims 89-94, wherein the second portion is not

symmetrically positioned within the particle.

96. The article of any one of claims 89-95, wherein the first portion has a void

volume of at least about 10 vol .

97. The article of any one of claims 89-96, wherein the first portion is not

symmetrically positioned within the particle.

98. The article of any one of claims 89-97, wherein the first polymer comprises a polyacrylate.

99. The article of any one of claims 89-98, wherein the first polymer comprises poly(isobornylmethaacrylate) .

100. The article of any one of claims 89-99, wherein the first portion comprises a first section and a second section, the first section having a higher porosity than the second section.

101. The article of claim 100, wherein the first section is surrounded by the second section.

102. The article of claim 101, wherein the second section has an average pore diameter of less than about 100 nm.

103. An article, comprising:

a particle comprising at least 5 wt oil therein, relative to the weight of the particle, wherein the particle comprises an inner region and a layer of nanoparticles substantially covering the surface of the particle.

104. The article of claim 103, wherein the particle has a maximum dimension of less than about 1 cm.

105. The article of any one of claims 103 or 104, wherein at least some of the

nanoparticles are formed from a material having a water contact angle of less than 90°.

106. The article of any one of claims 103-105, wherein at least some of the

nanoparticles are silica nanoparticles.

107. The article of any one of claims 103-106, wherein the nanoparticles have a

maximum dimension of less than about 1 micrometer.

108. The article of any one of claims 103-107, wherein the nanoparticles have a distribution in diameters such that no more than 5% of the nanoparticles have a diameter greater than about 110% and/or less than about 90% of the overall average cross- sectional diameters of the nanoparticles.

109. The article of any one of claims 103-108, wherein the inner region comprises at least two polymers.

110. The article of any one of claims 103-109, wherein the inner region is formed from a material having a water contact angle of greater than 90°.

111. The article of any one of claims 103- 110, wherein the inner region comprises at least a first portion defined by a first polymer and a second portion defined by a second polymer.

112. The article of claim 111, wherein the weight ratio of the first polymer to the second polymer is between about 0.5 to about 1.5.

113. The article of any one of claims 111 or 112, wherein the first polymer and/or the second polymer is a UV-crosslinkable polymer.

114. The article of any one of claims 111-113, wherein the first portion is surrounded by the second portion. 115. The article of any one of claims 111-114, wherein the second portion is not symmetrically positioned within the particle.

116. The article of any one of claims 111-115, wherein the first portion has a void volume of at least about 10 vol%.

117. The article of any one of claims 111-116, wherein the first portion is not

symmetrically positioned within the particle.

118. The article of any one of claims 111-117, wherein the first portion comprises a first section and a second section, the first section having a higher porosity than the second section.

119. The article of claim 118, wherein the first section is surrounded by the second section.

120. The article of claim 119, wherein the second section has an average pore diameter of less than about 100 nm.

121. A method, comprising:

providing a droplet comprising a mixture of a monomer and a porogen; causing the mixture of the monomer and the porogen to begin phase separating;

polymerizing the monomer to from a polymer prior to complete phase separation of the monomer and the porogen; and

removing at least some of the porogen from the polymer. 122. The method of claim 121, wherein the droplet is suspended in a continuous fluid.

123. The method of any one of claims 121 or 122, wherein the droplet is a

microfluidic droplet. 124. The method of any one of claims 121-123, wherein the porogen comprises

polydimethylsiloxane.

125. The method of any one of claims 121-124, comprising providing a droplet

comprising a first portion comprising the mixture of monomer and porogen, and a second portion comprising a second monomer. The method of any one of claims 121-125, wherein causing the mixture of the monomer and the porogen to begin phase separating comprises exposing the droplet to an aqueous carrying fluid. 127. The method of any one of claims 121-126, wherein polymerizing the monomer comprises exposing the droplet to ultraviolet radiation.

128. The method of claim 127, wherein the porogen is not polymerized upon exposure to the ultraviolet radiation.

129. The method of any one of claims 121-128, wherein polymerizing the monomer comprises exposing the droplet to a chemical initiator.

130. The method of any one of claims 121-129, wherein the mixture comprises a mass ratio of monomer to porogen of between about 10: 1 and about 1: 10.

131. The method of claim 130, wherein the mixture comprises a mass ratio of

monomer to porogen of between about 3: 1 and about 1:3. 132. The method of any one of claims 121-131, wherein removing at least some of the porogen comprises exposing the droplet to a fluid that the porogen dissolves in.

133. The method of any one of claims 121-132, wherein removing at least some of the porogen comprises exposing the droplet to isopropanol.

134. An apparatus for forming droplets, comprising:

a first microfluidic channel having an exit opening;

a second, adjacent microfluidic channel having an exit opening substantially coinciding with the exit opening of the first channel; and

a third microfluidic channel having an entrance opening substantially opposing the exit openings of each of the first and second channels.

135. The apparatus of claim 134, wherein the first and the second channels form a theta structure.

136. The apparatus of claim 135, wherein the third channel is axially aligned with the theta structure.

137. The apparatus of any one of claims 134-136, wherein the first, second, and third channels are contained in a fourth microfluidic channel. 138. The apparatus of any one of claims 134-137, wherein the first channel is tapered at the exit opening.

139. The apparatus of any one of claims 134-138, wherein the second channel is tapered at the exit opening.

140. The apparatus of any one of claims 134-139, wherein the third channel is tapered at the entrance opening.

141. The apparatus of any one of claims 134-140, wherein at least one of the channels comprises a glass capillary.