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WO2007060462A1 - Mousses stabilisees par des particules - Google Patents

Mousses stabilisees par des particules Download PDF

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Publication number
WO2007060462A1
WO2007060462A1 PCT/GB2006/004421 GB2006004421W WO2007060462A1 WO 2007060462 A1 WO2007060462 A1 WO 2007060462A1 GB 2006004421 W GB2006004421 W GB 2006004421W WO 2007060462 A1 WO2007060462 A1 WO 2007060462A1
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WIPO (PCT)
Prior art keywords
foam
particle
stabilised
particles
latex
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PCT/GB2006/004421
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English (en)
Inventor
Anthony J. Ryan
Steven P. Armes
Syuji Fujii
Peter Iddon
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University of Sheffield
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University of Sheffield
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/24—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by surface fusion and bonding of particles to form voids, e.g. sintering
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/30—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by mixing gases into liquid compositions or plastisols, e.g. frothing with air
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
    • C08J2201/044—Elimination of an inorganic solid phase
    • C08J2201/0444—Salts
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
    • C08J2201/044—Elimination of an inorganic solid phase
    • C08J2201/0444—Salts
    • C08J2201/0446—Elimination of NaCl only
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2319/00—Characterised by the use of rubbers not provided for in groups C08J2307/00 - C08J2317/00

Definitions

  • This invention relates to particle-stabilised foams, and more particularly to latex- stabilised foams and methods for their production.
  • a foam is a dispersion of gas in either a liquid or solid continuous phase.
  • Foams are of widespread importance, and are used as intermediate or end products in a diverse range of applications. These include separation of minerals by foam flotation, fire fighting, synthesis of insulating materials, food manufacturing, and preparation of lightweight construction materials.
  • Foaming in a liquid/stabiliser mixture can occur via three main mechanisms: introduction of gas to the body of the mixture through fine holes (sparging), agitation or shaking of the mixture in the presence of gas, or in situ generation of gas bubbles by a sudden pressure drop or chemical reaction.
  • Foam stabilisers can be broadly split into three main categories: ionic or non-ionic surfactants; colloidal stabilisers (including proteins); and solid particles.
  • Solid particles have been used both as foam stabilisers and de-stabilisers in surfactant- stabilised aqueous foams for many years.
  • Hydrophobic particles are often used in antifoam formulations, and their mode of action is believed to be through a bridging- dewetting mechanism.
  • Hydrophilic particles are believed to stabilise foams by collecting in the films and Plateau borders of a foam; consequently slowing down film drainage and kinetically increasing the foam stability. This is due to the capillary pressure caused by wetting of the particle surface by the aqueous phase. Wetting of the particle surface produces capillary forces that act to increase film thickness in the vicinity of the particles. If enough particles are present, the rate of drainage of the aqueous phase can be retarded.
  • Hydrophilic particles can also increase foam stability by reducing the diffusion of gas between foam bubbles (disproportionation), which eventually contributes towards the rupture of foam bubbles and collapse of the foam. There may also be structural reinforcement of a foam film due to contact, friction, or cohesion between particles.
  • Sun and Gao Metallurgical and Materials Transactions A - Physical Metallurgy and Materials Science 2002, 33, 3285) used 1 ⁇ m polytetrafluoroethylene (PTFE), 20 ⁇ m polyethylene (PE), or 75 ⁇ m polyvinyl chloride) (PVC) particles to produce wet foams of reasonable stability in water/ethanol mixtures. Maximum foam stabilities were obtained for the PTFE, PE, and PVC particles at liquid compositions of 40 v/v %, 10 v/v %, and 5 v/v % ethanol, respectively.
  • Murray and co-workers Liangmuir 2004, 20, 8517 used partially hydrophobic 20 nm silica nanoparticles as the sole stabiliser for the formation of stable air bubbles.
  • Silylation was used to increase the hydrophobicity of the originally hydrophilic silica.
  • the authors reported that particles with 33 % and 40 % silylated surfaces formed stable bubbles in an air-saturated aqueous dispersion after a sudden pressure drop. However, these particles were not good foaming agents and only produced a dispersion of discrete bubbles. Salt was also used to fine-tune the particle hydrophobicities to further optimise the degree of stabilisation achieved.
  • Velev and co-workers (Langmuir 2004, 20, 10371) described the synthesis of foams prepared using polydisperse polymer microrods with an average length of 23.5 ⁇ m and an average diameter of 0.6 ⁇ m, in the absence of any surfactant.
  • the microrods were synthesised from a bisphenol A-based epoxy resin (SU-8) using a liquid-liquid dispersion technique. Due to their rigid entangled structure and resistance to mechanical perturbations, the polymer microrod foams were very stable, even after drying.
  • Binks and Horazov investigated the formation of foam stabilised with polydisperse silica nanoparticles (20- 50 nm) of intermediate hydrophobicities. The authors reported that particles with 80 % and 68 % silylated surfaces formed the most stable foams after homogenisation or after handshaking. No mention was made of foams surviving drying.
  • the present invention provides a particle-stabilised foam wherein the particles are derived from a polymer latex dispersion and the foam substantially retains its structure on drying.
  • the present invention provides a method for the production of a particle-stabilised foam, which comprises introducing a gas into a polymer latex dispersion to form a foam and drying the foam thus produced.
  • the present invention provides a stable dry particle-stabilised foam wherein the particles are derived from a polymer latex dispersion.
  • the invention provides an optical device comprising a particle- stabilised foam wherein the particles are derived from a polymer latex dispersion.
  • the invention provides a method of producing an optical device exhibiting moire patterns, which comprises a particle-stabilised foam derived from a polymer latex dispersion, and an optical device produced thereby.
  • the invention provides a method of producing an optical device exhibiting multicolour diffraction effects, which comprises a particle-stabilised foam derived from a polymer latex dispersion, and an optical device produced thereby.
  • Figure 1 shows a diagram of a foam column apparatus (not to scale) suitable for use in the method of the invention
  • Figure 2 shows a diagram of an optical bench arrangement for carrying out the laser diffraction experiments. The distance between the translucent paper and the sample was 29.5 mm;
  • Figure 3 shows DCP curves of the 1.62 ⁇ m (A), 1.14 ⁇ m (B) and 0.81 ⁇ m (C) diameter PNVP-stabilised PS latex particles (entries 1-3 in Table 1);
  • Figure 4 shows a representative SEM image of the 1.62 ⁇ m diameter PNVP-stabilised PS latex particles (entry 1 in Table 1);
  • Figure 5 shows a representative SEM image of the 1.14 ⁇ m diameter PNVP-stabilised PS latex particles (entry 2 in Table 1);
  • Figure 6 shows a representative SEM image of the 0.81 ⁇ m diameter PNVP-stabilised PS latex particles (entry 3 in Table 1);
  • Figure 7 shows a representative SEM image of the 0.17 ⁇ m diameter PNVP-stabilised PS latex particles (entry 5 in Table 1);
  • Figure 8 shows a representative SEM image of the 0.26 ⁇ m diameter PNVP-stabilised PS latex particles (entry 6 in Table 1);
  • Figure 9 shows digital photographs of foam column experiments after 24 h.
  • Figures A to Figure F correspond to entries 1 to 6 in Table 4, respectively;
  • Figure 10 shows a cross-sectional representation of a typical latex-stabilised foam, showing how particle bilayers are formed in dry foam. As the wet foam comprising particle monolayer-stabilised nitrogen bubbles dries, the bubble surfaces are drawn together to form ordered bilayers (left to right);
  • Figure 11 shows optical photomicrographs of crushed foam stabilised using the model 1.14 ⁇ m PNVP-stabilised PS latex particles (entry 2 in Table 1), illustrating moire patterns. Note the reference dot in the top left corner of each image, which is approximately equal to the diameter of a single latex particle. Thus, the observed features are much greater than the latex particles used in these foams;
  • Figure 12 shows a computer-generated image of an artificially created array of hexagonally close-packed spheres (A); a copy of the same computer-generated image after rotation through 24° clockwise with a reduction in opacity of 50 % (B); and direct superposition of these two images to produce a moire-type pattern (C);
  • Figure 16 shows representative SEM images showing clear evidence for the existence of bilayers in the highly stable foams (entries 1-3 in Table 1). Shown are dry latex foams formed from 1.62 ⁇ m (A), 1.14 ⁇ m (B), and 0.81 ⁇ m (C) diameter PNVP-stabilised PS particles. These images confirm the latex foam bilayer representation shown in figure 10;
  • Figure 17 shows diffraction patterns obtained from laser diffraction experiments using dried foam prepared using 1.14 ⁇ m diameter PNVP-stabilised PS particles. Typical examples of the two main diffraction patterns are shown: a clear hexagonal spot pattern (A), and a ring-like pattern comprising multiple hexagonal spot patterns (B); and
  • Figure 18 shows digital photographs taken in direct transmitted sunlight of the dried particulate foam stabilised using 1.62 ⁇ m PNVP-stabilised PS particles (entry 1 in Table 1), dispersed in water before sintering (A), and dispersed in water after sintering at 105 0 C for 10 min. (B).
  • a 'stable' foam is a foam that retains its structure and volume indefinitely after drying, with little or no change in volume.
  • the foam is stabilised solely by the latex particles.
  • the foam is stabilised primarily by the latex particles.
  • the foam comprises contaminants which comprise up to 10% by weight of a polymeric stabiliser, a small molecule surfactant or a combination thereof.
  • the particles forming the particle-stabilised foam are substantially spherical, and may, for example, have a diameter of from 0.05 ⁇ m to 10 ⁇ m, in particular from 0.1 ⁇ m to 5 ⁇ m, e.g. from 0.5 ⁇ m to 2 ⁇ m.
  • the foam cells are substantially polyhedral in shape. Of mention are foam cells having a diameter of from 1 ⁇ m to 50 mm.
  • the polymer latex dispersion is a substantially monodisperse latex dispersion of preferably substantially spherical latex particles.
  • the polymer latex may, for example, comprise either a sterically-stabilised or a charge-stabilized dispersion, e.g. a colloidal polymer dispersion.
  • the polymer latex is cationically or anionically charged.
  • cationically charged polymer latexes comprise at least one surface amidino group.
  • anionically charged polymer latexes comprising at least one surface carboxylic acid group.
  • the latex particles have a core/shell type structure wherein a core polymer particle is stabilised by a shell of a different polymer (the steric stabilizer) or charge.
  • the shell can be attached by physical (e.g. adsorption) or chemical (e.g. covalent or ionic bonds) means.
  • the shell may provide either complete, or partial, coverage of the core.
  • composition of the polymer latex core is not particularly limited and can comprise any suitable polymer that can be produced in latex form.
  • Methods well documented in the art for producing sterically-stabilised polymer latexes include suspension polymerization, emulsion polymerization (including seeded emulsion polymerisation), precipitation polymerization (including seeded precipitation polymerisation) and dispersion polymerization (including seeded dispersion polymerisation).
  • the polymer particles are generally synthesised via a free-radical initiated mechanism, but other chemistries can also be used, e.g.
  • Latex particles prepared by the dispersion of pre-formed polymers can also be used, e.g. alkyd resins. Any monomer or combination of monomers that is amenable to free radical polymerisation may be used to form the latex polymer core. Suitable monomers are typically vinyl monomers, for example styrene and its derivatives, acrylates, methacrylates, dienes, chloroprene, vinyl chloride, vinyl acetate, vinyl pyridines (eg.
  • polystyrene poly(alkyl methacrylate) or poly(alkyl acrylate), polyolefins or polyesters, in particular polystyrene, including cross-linked polystyrene, epoxy resins, alkyd resins, polyamides, novolac resins or polyurethanes.
  • the polymer latex core may be cross-linked during synthesis, using multivinyl monomers, for example, d ⁇ vinylbenzene, ethylene glycol diacrylate or ethylene glycol dimethacrylate as a cross-linking agent. Cross-linking is also possible using UV radiation and heat.
  • the stabilizing polymer forming the shell of the latex particles can be based on a wide range of water-soluble/hydrophilic polymers, for example, polyvinylpyrrolidone), poly(acrylic acid), polyvinyl alcohol), poly(ethylene imine), water-soluble poly(meth)acrylates (e.g. poly(acrylic acid), poly[2-(dimethylamino)ethyl methacrylate]), polyvinyl alcohol), poly(methacrylic acid), poly(ethylene oxide), poly(2-vinyl pyridine), poly (4-vinyl pyridine) or poly(sodium 4-styrenesulfonate), various cellulosic derivatives (e.g., polyvinylpyrrolidone), poly(acrylic acid), polyvinyl alcohol), poly(ethylene imine), water-soluble poly(meth)acrylates (e.g. poly(acrylic acid), poly[2-(dimethylamino)ethyl methacrylate]), polyvinyl alcohol), poly
  • the stabilizing polymer forming the shell of the latex particles is produced by polymerizing or copolymerising water- soluble/hydrophilic monomers.
  • Stimulus-responsive foam can be produced using polymer latex particles which have stimulus-responsive groups either in the latex shell or on the latex surface.
  • the stimulus-responsive polymer forming the shell of the latex particles can be based on a wide range of pH-, temperature- or salt-responsive polymers, for example, poly(acrylic acid) or poly[2-(dimethylamino)ethyl methacrylate].
  • the polymer latex comprises a stimulus-responsive polymer, for example poly(acrylic acid), poly(methacrylic acid), poly[2-(dimethylamino)ethyl methacrylate], poly[2-(diethyiamino)ethyl methacrylate], poly(2-vinylpyridine), poly(4- vinylpyridine) or poly( ⁇ f-isopropylacrylamide).
  • a stimulus-responsive polymer for example poly(acrylic acid), poly(methacrylic acid), poly[2-(dimethylamino)ethyl methacrylate], poly[2-(diethyiamino)ethyl methacrylate], poly(2-vinylpyridine), poly(4- vinylpyridine) or poly( ⁇ f-isopropylacrylamide).
  • Polymer latexes stabilized with a polyacid form stable foams below the pKa value, (e.g. for poly(acrylic acid), stable foams are formed at pH values at or below its pKa of approximately 4.5) and those stabilized with a polybase form stable foams at pH values at or above the pKa value.
  • the polymer latex dispersion stabilized with poly(acrylic acid) may have a pH of less than 4, e.g. a pH ranging from 1 to 3.5.
  • the charge on the latex particle surface comprises ionizable groups, for example vinyl pyridine groups, amine groups, carboxylic acid groups or amidino groups.
  • the polymer latex dispersion is an aqueous dispersion, or a dispersion of polymer particles in an organic solvent, for example, a C1-6 lower alcohol, such as methanol, ethanol or 2-propanol, or tetrahydrofuran. Mixtures of water and water-miscible organic solvents can also be used.
  • the stable foam of the present invention can be generated, for example, by hand - shaking or the in situ generation of gas bubbles by means of a chemical reaction or a sudden pressure drop, but often a gas is blown through the latex dispersion (sparging), for example, by placing the latex dispersion in a column and blowing a suitable gas through the base of the column.
  • the gas may be, for example, carbon dioxide, argon, oxygen, helium, air or nitrogen.
  • the stable dry particulate foam is produced by the methods described above.
  • the method of producing an optical device exhibiting moire patterns and the method of producing an optical device exhibiting multicolour diffraction effects comprises crushing the particle stabilised foam.
  • the method of producing an optical device exhibiting moire patterns and the method of producing an optical device exhibiting multicolour diffraction effects comprises dispersing the particle stabilised foam in a liquid medium.
  • the particle stabilised foam can be dried, non-dried, sintered, non-sintered, plasticized, non-plasticized, cross-linked or non- crosslinked.
  • Ammonium persulfate (APS), 2,2'-azobis(isobutyronitrile) (AIBN), and 2,2'- azobis(2-methylpropionamidine) dihydrochloride (AIBA) were used as free radical initiators (see Figure 5.4).
  • HPLC grade methanol, ethanol and 2-propanol (IPA), were purchased from Fisher Scientific.
  • Poly(vinylidene fluoride) dialysis tubing (molecular weight cut-off 500,000 Daltons) was acquired from Fisher Scientific. The water used in these experiments was deionised using an Elga EIgastat Option 3 water purification apparatus. Dry nitrogen gas (oxygen free) was supplied by BOC.
  • PNVP Polypropanol
  • 2-propanol 2.0 L
  • This reaction mixture was vigorously stirred at 70 °C until the PNVP had dissolved completely, and was then degassed using a nitrogen purge.
  • Polymerisation commenced after the addition of a mixture of styrene and AIBN initiator (2.00 g AIBN dissolved in 200 g styrene). The reaction was allowed to proceed for 24 h with continuous stirring at 300 rpm under a nitrogen atmosphere.
  • Different diameters of PNVP-stabilised PS latexes were synthesised by following the same general method by replacing up to 20 v/v % of the 2-propanol solvent with water. Higher water contents led to smaller latexes. These latexes were purified by centrifugation (4,000-5,000 rpm for 30-90 min.).
  • PNVP-stabilised PS latex particles were prepared by the dispersion polymerisation of styrene in the presence of PNVP homopolymer as a steric stabiliser at 70 °C using AIBN initiator.
  • PNVP (1.00 g; 20 w/w % based on styrene) was added to methanol (45 ml_) and water (5.0 mL) in a one-necked 100 ml_ round-bottomed flask containing a magnetic stirrer bar. This reaction mixture was vigorously stirred at 70 0 C until the PNVP had dissolved completely. The reaction mixture was then degassed using five alternating cycles of evacuation and pressurisation with nitrogen (starting with evacuation).
  • Polymerisation commenced after the injection of a mixture of AlBN and styrene (0.050 g AIBN dissolved in 5.00 g styrene) into the reaction vessel.
  • the reaction was allowed to proceed for 24 h with continuous stirring at 500 rpm under a nitrogen atmosphere.
  • This latex was purified by centrifugation (8,000-10,000 rpm for 90-120 min.).
  • Emulsion polymerisation of styrene was performed in the presence of PNVP homopolymer as a steric stabiliser in batch mode at 70 °C using APS initiator.
  • PNVP (0.500 g; 10 w/w % based on styrene) was added to water (45 mL) in a one-necked 100 mL round-bottomed flask containing a magnetic stirrer bar. This reaction mixture was vigorously stirred at 20 0 C until the PNVP had dissolved completely.
  • Styrene (5.00 g) was then added to the reaction mixture, and the flask was heated to 70 0 C.
  • reaction mixture equilibrated for 30 min., and was then degassed using five alternating cycles of evacuation and pressurisation with nitrogen (starting with evacuation).
  • Polymerisation commenced after the injection of an aqueous solution of APS (0.050 g APS dissolved in 5.0 ml_ water) into the reaction vessel.
  • the reaction was allowed to proceed for 24 h with continuous stirring at 500 rpm under a nitrogen atmosphere. This latex was purified by centrifugation (8,000-10,000 rpm for 90-120 min.).
  • Emulsion polymerisation of styrene was performed in the presence of PNVP homopolymer as a steric stabiliser in batch mode at 60 0 C using AIBA initiator.
  • PNVP (0.500 g; 10 w/w % based on styrene) was added to water (45 ml_) in a one-necked 100 mL round-bottomed flask containing a magnetic stirrer bar. This reaction mixture was vigorously stirred at 20 0 C until the PNVP had dissolved completely.
  • Styrene (5.00 g) was then added to the reaction mixture, and the flask was heated to 60 °C.
  • the reaction mixture was equilibrated for 30 min., and was then degassed using five alternating cycles of evacuation and pressurisation with nitrogen (starting with evacuation).
  • the polymerisation commenced after the injection of an aqueous solution of AIBA (0.050 g APS dissolved in 5.0 mL water) into the reaction vessel.
  • AIBA 0.050 g APS dissolved in 5.0 mL water
  • the reaction was allowed to proceed for 24 h with continuous stirring at 500 rpm under a nitrogen atmosphere. This latex was purified by centrifugation (8,000-10,000 rpm for 90-120 min.).
  • the latexes were purified by either centrifugation or dialysis to ensure that non-adsorbed excess stabiliser or other surface-active materials (e.g. trace monomer) were removed.
  • Latex was loaded into sections of thoroughly washed poly(vinylidene fluoride) dialysis tubing. The sections were sealed and then immersed in water as the external solvent, which was changed daily. The surface tension of this external water was measured after at least 24 h contact with the full dialysis tubing. Purification continued until this surface tension was close to that of water at 20 0 C (72.5 ⁇ 0.5 mN m '1 ).
  • a drop of dilute latex was placed on a microscope slide, and optical photomicrographs obtained using a James Swift MP3502 optical microscope (Prior Scientific Instruments Ltd.) fitted with a Nikon Coolpix 4500 digital camera.
  • DCP Disc Centrifuge Photosedimentometry
  • DCP weight- average diameter
  • Dw/Dn polydispersity
  • Samples for DCP analysis were prepared by diluting a few drops of the aqueous latex mixture in 20 ml_ of a 1 :3 v/v % methanol/water mixture. This solution was then immersed in an ultrasonic bath for 30 seconds prior to DCP analysis. The centrifugation rate was adjusted to between 2,000 and 10,000 rpm, depending on the diameter of the particles being measured. A particle density of 1.05 g cm "3 was assumed for the polystyrene latex particles. Thus the stabiliser layer thickness was always ignored.
  • Dw/Dn values less than 1.01 are generally regarded as characteristic of highly monodisperse latexes, whereas values between 1.01 and 1.05 are typical of near- monodisperse latexes, and values above 1.05 are usually associated with relatively polydisperse latexes.
  • 0.30 ⁇ m and 0.90 ⁇ m diameter PS latex standards both have a Dw/Dn value of 1.003 as measured by DCP.
  • Particle diameters for the larger particles in this patent (> 1 ⁇ m) were determined by DCP.
  • the intensity-average particle diameter (Dz) and polydispersity were calculated by cumulants analysis of the experimental correlation function using the Stokes-Einstein equation for dilute, non- interacting monodisperse spheres.
  • the polydispersity is a measure of the width of the particle diameter distribution. Values less than 0.01 are generally regarded as characteristic of highly monodisperse latexes, whereas values between 0.01 and 0.10 are typical of near-monodisperse latexes, and values above 0.10 are usually associated with relatively polydisperse latexes. For comparison, 0.30 ⁇ m and 0.90 ⁇ m diameter PS latex standards (Duke Scientific Corp., USA) both have polydispersity values of 0.01-0.02 as measured by DLS.
  • SEM images were obtained using a Leo Stereoscan 420 instrument operating at 20 kV and 5-10 pA. Dried samples were placed on an aluminium stub and sputter-coated with gold (to minimise sample-charging problems).
  • Latex was shaken for 30 seconds by hand. The shaking time, although arbitrary, was found to give reasonably reproducible results. Hand-shaking was also found to be a good indicator of the propensity of a given latex to stabilise foams. Latexes that did not produce foam upon hand-shaking did not produce foam using the foam column method either.
  • the foam column setup is shown in Figure 1.
  • the column and frit were surrounded by a water-filled jacket 3, comprising an inlet 4 and an outlet 5 for water.
  • the space between the column and this water jacket was designed to be as small as possible, and was packed at the top with a foam seal 6 to reduce convective heat loss.
  • the inner wall of the water jacket was constructed from thinner glass than was used for the outer wall, so as to aid conductive heat transfer.
  • Dry nitrogen gas was connected in series to a flow rate meter, a copper coil heat-exchanger, before finally connecting to just below the sintered glass frit at inlet 7.
  • the heat-exchanger ensured the nitrogen gas was preheated to the same temperature as the glass jacket. All glassware was thoroughly washed with THF and dried before use.
  • the apparatus was assembled and the water jacket temperature was set to 25 0 C. The apparatus temperature was allowed to equilibrate for at least 1 h before the start of the experiment. During this time nitrogen gas was passed through the frit so that the air in the column was displaced. Before addition of the latex, the nitrogen flow rate was set to 50 mL min '1 . 5 mL of the latex sample 8 was then carefully injected on top of the frit via the top of the glass column. There was a short induction time as the nitrogen below the frit reached sufficient pressure to be forced through the pores in the frit. As soon as bubbles were observed leaving the surface of the frit, the timer was started. After 5 min.
  • the nitrogen supply was turned off, and the height of any stable foam that was formed was then measured. In some cases, the residual latex was collected for analysis. The foam was left at 25 0 C for at least 24 h, after which time the foam's height was re-measured and the foam recovered for further analysis.
  • a Nikon Coolpix 4500 digital camera was used to collect digital photographs of foams generated using the foam column method. No further image processing was carried out on the images.
  • the optical bench arrangement for the laser diffraction experiments is shown in Figure 2.
  • a He-Ne laser 9 operating at 633 nm was used to illuminate a sample of dried particulate foam 10 prepared from the 1.14 ⁇ m PNVP-stabilised PS latex particles (entry 2 in Table 1) that had been sandwiched between two optical microscopy slide glasses 11.
  • a 3 mm diameter aperture 12 was used to improve the profile of the laser beam incident on the sample.
  • the resulting diffraction pattern was projected onto a sheet of white translucent paper 13, and recorded at beam stop 14 using a Nikon Coolpix 4500 digital camera 15.
  • Entries 5 and 6 were additionally charge-stabilised by polymer chain-end groups resulting from the anionic APS and cationic AIBA initiators, respectively.
  • Entries 1 , 2 and 3 in Table 1 were synthesised via dispersion polymerisation of styrene using the PNVP stabiliser.
  • the largest particles were synthesised in pure 2-propanol, with a Dw of 1.62 ⁇ 0.13 ⁇ m and a Dw/Dn of 1.008.
  • PNVP-Stabilised PS Latex in a MethanolAA/ater Mixture Using AIBN Initiator PNVP-Stabilised PS Latex in a MethanolAA/ater Mixture Using AIBN Initiator .
  • Emulsion polymerisation of styrene using the PNVP stabiliser in aqueous solution gave particles with a Dz of 0.17 ⁇ m and a polydispersity of 0.176 as measured by DLS (entry 5 in Table 1). This polymerisation was initiated using APS 1 resulting in anionic sulfate end groups on the polymer chains that are expected to contribute to the stability of the particles through charge stabilization as well as steric stabilisation. Typical SEM images for these particles are shown in Figure 7, in which the uniform spherical morphology of these particles can be observed.
  • a second aqueous emulsion polymerisation of styrene using the PNVP stabiliser gave particles with a Dz of 0.26 ⁇ m and a polydispersity of 0.114 as measured by DLS (entry
  • the 1.14 ⁇ m diameter PNVP-stabilised PS latex (entry 2 in Table 1) was used as a model latex in initial experiments that explored some of the physical parameters that influence foam formation. Table 2 shows data from reproducibility.
  • Table 3 shows a summary of the effect of varying several physical parameters that were expected to influence foam formation. In addition to the initial foam height obtained after the foam column experiment, the approximate bubble diameter range for the foam at the top, middle, and bottom of the column are also reported. Table 3. Effect of varying the physical parameters on foam formation using the model 1.14 ⁇ m PNVP-stabilised PS particles (entry 2 in Table 1) using the foam column. 5 ml_ of aqueous latex was sparged with nitrogen gas at a flow rate of 50 ml. miri "1 , through a sintered glass frit of known porosity for 5 min. at 25 C C.
  • the foam height obtained for the foam prepared using the latex at 1.0 w/v % (250 mm) is significantly lower than for the other foams reported in Table 3. This can be explained by the incomplete spanning of the foam column diameter by a small quantity of relatively fragile foam. As the foam moved up the column, it broke apart and allowed the gas to escape, halting the rise of the foam.
  • the bubble diameter ranges measured during the various experiments are more informative. As the latex concentration was increased from 1.0 w/v % to 7.5 w/v %, the volume of foam-free voids column decreased: all three experiments using 7.5 w/v % latex generated foam for the entire 5 min. The average bubble diameters also decreased in line with the increasing latex concentration. This confirms that the quantity of foam is dependent on the concentration of latex particles available, and shows that the bubble diameter increases as the latex concentration is reduced. The latex concentration also drops during a given foam column experiment, as the latex becomes increasingly depleted. There was no significant change in either the foam height or the bubble diameter after 24 h in the foam column, compared to initial measurements taken 5 min. after the flow of nitrogen had ceased.
  • foams generated using aqueous solutions of SDS (a common industrial surfactant) or PNVP (the colloidal stabiliser used for the synthesis of the model latex) do not display the same rigidity, and collapse upon drying at 25 0 C.
  • the resulting depleted latex dispersions were analysed for their remaining latex content and were found to contain an average of 0.7 w/w % solids, compared to an original concentration of 7.5 w/w % solids. This means that at least 90 % of the particles in the original latex were used to form highly stable foam.
  • Entries 5 and 6 in Table 4 also initially produced foam for the entire duration of the foam column experiment, and then experienced significant collapse as the foam dried.
  • the particles synthesised using the anionic APS initiator suffered collapse to a greater extent compared to neutral AIBN-initiated latex particles (entry 4 in Table 4); whereas the particles synthesised using a cationic AIBA initiator (entry 6 in Table 4) collapse to a lesser extent.
  • the sterically-stabilised cationic particles (entry 6) were expected to form more stable foams due to their initial attraction to the anionic nitrogen/water interface. However, once adsorbed to the interface the particles should experience mutual repulsion. Consequently, the packing efficiency of these particles was expected to be inferior compared to the neutral particles.
  • the sterically-stabilised cationic foam suffered much less collapse than for the sterically-stabilised anionic particle foam (entry 5) and, surprisingly, also less collapse than the smallest neutral PNVP-stabilised particles (entry 4). This latter result is interesting given that the neutral particles are significantly larger, and should also pack more closely to form a more robust foam.
  • Highly monodisperse fluorescent 1.57 ⁇ m diameter PNVP-stabilised PS latex was used to prepare highly stable foam by hand-shaking.
  • the latex was synthesised using a similar protocol to the 1.62 ⁇ m diameter PNVP-stabilised PS latex (entry 1 in Table 1), except that 1 w/w % of the styrene was replaced with 1-pyrenylmethyI methacrylate, a fluorescent monomer.
  • Well-ordered hexagonally close-packed arrays of particles were observed by optical microscopy and SEM. Confocal laser scanning microscopy was used to obtain photomicrographs of cross-sectional areas of individual foam bubbles. These microscopy studies confirmed that the particle monolayers were adsorbed at the air/water interface of the bubbles.
  • PEGMA-stabilised poly(2-vinylpyridine) latex particles prepared by emulsion polymerization using the PEGMA stabilizer (A. Loxley, B. Vincent, Colloid Polym. Sci. 275, 1108 (1997)) with a diameter of 0.37 ⁇ m were also used to prepare highly stable foam at pH 7.5 that retained its shape and volume after drying. Multicolour diffraction effects were observed during optical microscopy experiments, resulting from Bragg diffraction by colloidal crystals consisting of ordered microgel particle arrays.
  • Foam generated using the larger PNVP-stabilised PS latex particles are highly stable in both wet and dry states.
  • the foam structure was evaluated using optical and confocal laser microscopy, SEM, and laser diffraction.
  • Optical microscopy studies after applying pressure and SEM studies after deliberating breaking the dried foam provided convincing evidence that these highly stable foams consist primarily of particle bilayers comprising two well-ordered hexagonally close-packed monolayers. The bilayers are formed when the surfaces of adjacent nitrogen bubbles, stabilised by a monolayer of particles, are drawn together as the foam dries (see Figure 10).
  • Moire patterns were observed in optical photomicrographs of dry foams. Moire patterns are produced when two (or more) arrays of regular hexagonally-packed PS particles, formed during the foam column experiments.
  • Figure 11 shows an optical micrograph of dried foam stabilised with 1.14 ⁇ m PNVP-stabilised PS particles exhibiting moire patterns. The particular moire patterns shown in these micrographs can only occur with well-ordered arrays of particles.
  • the highly ordered nature of the PS particle arrays in the stable latex foams is apparent from the SEM images (see Figure 13, Figure 14 and Figure 15).
  • the degree of ordering is very high for the largest particles, and decreases as the mean particle diameter decreases.
  • the numbers of particles contained. within individual colloidal crystal domains were determined by analysis of SEM images (not shown).
  • the largest typical domains observed in foam prepared using the 0.81 ⁇ m diameter PNVP-stabilised PS latex particles contained 90-110 particles per domain.
  • a typical large domain contained 2,100 particles.
  • the significant reduction in the colloidal crystal domain size correlates with the particle diameter and the increase in polydispersity as the latex particle diameter decreases, since slightly different diameters necessarily pack less efficiently. Particle bilayers are also clearly evident in some of the higher magnification images (see Figure 16).
  • the pattern observed in Figure 17A is undoubtedly Bragg diffraction from a single hexagonally close-packed colloidal crystal of PS particles.
  • the pattern observed in Figure 17B is most likely Bragg diffraction resulting from multiple smaller colloidal crystals at different relative orientations.
  • the angle of diffraction ( ⁇ ) from a two- dimensional array where a laser beam of wavelength ⁇ is incident perpendicularly to the plane of the array depends on the lattice spacing (d) of the particles, according to the following equation:
  • the foam prepared using the larger 1.62 ⁇ m diameter PNVP-stabilised PS particles displayed the most intense multicolour diffraction effects, while foam comprising smaller 0.81 ⁇ m diameter PNVP-stabilised PS particles (entry 3 in Table 5.1) displayed reduced intensity compared to the 1.14 ⁇ m diameter particles.
  • This colour intensity variation correlates with the significant difference in the size of the colloidal crystal domains observed by SEM and the PS particle diameter.
  • Foam generated using the 0.26 ⁇ m diameter PNVP-stabilised particles synthesised using the cationic AIBA initiator displays only weak colour effects in transmitted light. It appears yellow/green in reflected light, although the effect is much less intense than for the diffraction colours observed due to transmitted light for the previous foam examples (entries 1-3 in Table 4).
  • the right-hand photograph in each pair shows the dispersed foam fragments in each of the oils, while the left-hand photograph shows an image of the pure oil taken under the same conditions for comparison.
  • the same foam was then sintered by placing a sample in an 105 °C oven, for 10 min. This was designed to briefly heat the particulate foam to just above the glass transition temperature of PS (100 C C), thus allowing the surfaces of the latex particles to fuse with each other and hence stabilising the latex foam fragments. This heat treatment was sufficient to allow subsequent dispersion of the foam in water without any of the particle redispersion problems observed earlier.
  • Figure 18 shows digital photographs of this foam dispersed in water, before (A) and after (B) sintering. The particles in the sintered foams proved resistant to redispersal in the water phase for at least several months.
  • Charge-stabilised PS particles (stabilized purely by the cationic AIBA initiator fragments; i.e. no polymeric stabiliser was used) were prepared by the dispersion polymerization of styrene at 60 0 C using AIBA initiator. Styrene (5.0 mL) and methanol (50 mL) were added to a round-bottomed flask containing a magnetic stirrer bar. AIBA initiator (46.0 mg) was added and the mixture was degassed with nitrogen. The reaction mixture was heated to 60 0 C under a steady flow of nitrogen and then stirred for 24 h.
  • the resulting milky-white colloidal dispersion was purified by several centrifugation-redispersion cycles (2,000 rpm for 15 min.), with each successive supernatant being carefully decanted and replaced, gradually changing from pure alcohol to water via alcohol/water mixtures.
  • Cationic charge-stabilised PS latex particles with a bimodal particle diameter distribution were used to generate highly stable foams upon hand-shaking.
  • the latex comprised mainly 1 ⁇ m diameter particles with a minor population of submicrometer-diameter particles.
  • the particles were stabilised by cationic polymer chain-end groups resulting from the cationic AIBA initiator. Partial flocculation of this latex in the bulk solution suggested that these particles were not particularly colloidally stable after transferring from methanol to an aqueous medium. Again, hexagonally close-packed particles were observed on the surface of the foam bubbles by optical microscopy.
  • Dispersion polymerization of styrene was performed in the presence of PDMA-6-PMMA diblock copolymer as a colloidal stabilizer, in batch mode at 60 0 C using AIBN initiator.
  • a typical synthetic procedure was as follows: PDMA-fc-PMMA (0.5 g; 10 w/w % based on styrene) was added to methanol (50 mL) in a three-necked 100 ml_ flask fitted with a reflux condenser and a magnetic stirrer bar. This reaction mixture was vigorously stirred at 60 0 C until the PDMA-b-PMMA had dissolved completely, and was then degassed using a nitrogen purge.
  • the polymerization commenced after the injection of a mixture of styrene and AIBN (0.05 g AIBN in 5 g styrene) into the reaction vessel, and was allowed to proceed for 24 h with continuous stirring at 250 rpm under a nitrogen atmosphere. Conversion of styrene was almost 100 %, as determined by a gravimetrical method.
  • Dispersion polymerization of styrene was performed in the presence of poly(acrylic acid) (PAA) homopolymer as a colloidal stabilizer in batch mode at 70 0 C using AIBN initiator.
  • PAA poly(acrylic acid)
  • PAA poly(acrylic acid)
  • the polymerization commenced after the injection of a mixture of styrene and AIBN (0.168 g AIBN in 10 g styrene) into the reaction vessel, and was allowed to proceed for 48 h with continuous stirring at 250 rpm under a nitrogen atmosphere. Conversion of styrene was almost 100 %, as determined by a gravimetric method.
  • the latex foams prepared using PNVP-stabilised PS particles were stable to drying with little or no change in volume, and interesting optical effects were observed such as moire patterns and multicolour diffraction effects. Although rather brittle, such foams were stable with respect to collapse. These foams can be dispersed in various non-aqueous solvents that are non-solvents for both PNVP and PS. Moreover, these particulate foams are sufficiently robust after sintering to enable their dispersion in water without significant reduction in optical effects.
  • latex core does not significantly influence the foam- forming ability of the latex (only true if latex remains non-solvated). Rather, it seems that the nature of the particle stabiliser, the mean latex diameter, and perhaps the latex polydispersity play roles in determining whether highly stable foam is generated by a particular latex.

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Abstract

L’invention concerne une mousse stabilisée par des particules, lesdites particules dérivant d’une dispersion de latex polymérique et ladite mousse conservant sensiblement sa structure lors de son séchage.
PCT/GB2006/004421 2005-11-28 2006-11-28 Mousses stabilisees par des particules Ceased WO2007060462A1 (fr)

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WO2008082619A1 (fr) * 2006-12-29 2008-07-10 Owens Corning Intellectual Capital, Llc Mousse réticulée à température ambiante
WO2008082620A1 (fr) * 2006-12-29 2008-07-10 Owens Corning Intellectual Capital, Llc Mousse réticulée à température ambiante
CN102378782A (zh) * 2009-03-17 2012-03-14 朗盛德国有限责任公司 用于生产聚合物固体的方法
US8209915B2 (en) 2007-10-31 2012-07-03 Owens Corning Intellectual Capital, Llc Wall construction air barrier system
US8875472B2 (en) 2006-12-29 2014-11-04 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
DE102013106018A1 (de) * 2013-06-10 2014-12-24 Heraeus Kulzer Gmbh Formteile aus PMMA - Pulver als einfache Dosierhilfe bei der Herstellung von Dentalprothesen
EP2563867B1 (fr) 2010-04-27 2015-09-30 Akzo Nobel Coatings International B.V. Revêtements améliorés à faible teneur en dioxyde de titane
US9714331B2 (en) 2006-12-29 2017-07-25 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
US9868836B2 (en) 2006-12-29 2018-01-16 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
CN112525635A (zh) * 2020-11-20 2021-03-19 哈尔滨工业大学（深圳） 一种提取微塑料的方法
US12031128B2 (en) 2021-04-07 2024-07-09 Battelle Memorial Institute Rapid design, build, test, and learn technologies for identifying and using non-viral carriers
US12109223B2 (en) 2020-12-03 2024-10-08 Battelle Memorial Institute Polymer nanoparticle and DNA nanostructure compositions and methods for non-viral delivery
US12441996B2 (en) 2023-12-08 2025-10-14 Battelle Memorial Institute Use of DNA origami nanostructures for molecular information based data storage systems
US12458606B2 (en) 2023-09-29 2025-11-04 Battelle Memorial Institute Polymer nanoparticle compositions for in vivo expression of polypeptides

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Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9714331B2 (en) 2006-12-29 2017-07-25 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
WO2008082620A1 (fr) * 2006-12-29 2008-07-10 Owens Corning Intellectual Capital, Llc Mousse réticulée à température ambiante
US8875472B2 (en) 2006-12-29 2014-11-04 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
US9868836B2 (en) 2006-12-29 2018-01-16 Owens Corning Intellectual Capital, Llc Room temperature crosslinked foam
WO2008082619A1 (fr) * 2006-12-29 2008-07-10 Owens Corning Intellectual Capital, Llc Mousse réticulée à température ambiante
US8209915B2 (en) 2007-10-31 2012-07-03 Owens Corning Intellectual Capital, Llc Wall construction air barrier system
CN102378782A (zh) * 2009-03-17 2012-03-14 朗盛德国有限责任公司 用于生产聚合物固体的方法
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CN102378782B (zh) * 2009-03-17 2014-08-27 朗盛德国有限责任公司 用于生产聚合物固体的方法
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DE102013106018A1 (de) * 2013-06-10 2014-12-24 Heraeus Kulzer Gmbh Formteile aus PMMA - Pulver als einfache Dosierhilfe bei der Herstellung von Dentalprothesen
CN112525635A (zh) * 2020-11-20 2021-03-19 哈尔滨工业大学（深圳） 一种提取微塑料的方法
CN112525635B (zh) * 2020-11-20 2022-01-04 哈尔滨工业大学（深圳） 一种提取微塑料的方法
US12109223B2 (en) 2020-12-03 2024-10-08 Battelle Memorial Institute Polymer nanoparticle and DNA nanostructure compositions and methods for non-viral delivery
US12433910B2 (en) 2020-12-03 2025-10-07 Battelle Memorial Institute Polymer nanoparticle and DNA nanostructure compositions and methods for non-viral delivery
US12031128B2 (en) 2021-04-07 2024-07-09 Battelle Memorial Institute Rapid design, build, test, and learn technologies for identifying and using non-viral carriers
US12458606B2 (en) 2023-09-29 2025-11-04 Battelle Memorial Institute Polymer nanoparticle compositions for in vivo expression of polypeptides
US12441996B2 (en) 2023-12-08 2025-10-14 Battelle Memorial Institute Use of DNA origami nanostructures for molecular information based data storage systems

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