WO2012000741A1 - Partially silylated magnetic particles and dispersions thereof - Google Patents

Abstract

Magnetic core-shell particles comprising a core of one or more magnetic metal oxides and a shell of silicon dioxide, wherein the surface of the shell is partially silylated. Dispersion comprising these particles.

Description

 Partially silylated magnetic particles and dispersions thereof

The invention relates to partially silylated magnetic particles and a dispersion comprising these particles.

A liquid foam is defined as an accumulation of air bubbles dispersed in a liquid. The bubbles contain molecules of a gas that are soluble in water to some extent, so that the bubble tends to dissolve and disappear quickly. Furthermore, adjacent bubbles may coalesce. Soap molecules, known technically as surfactants, are surface-active compounds commonly used to prevent coalescence of bubbles by creating an electrical barrier at the air-water interface. However, they can not suppress the dissolution of bubbles, and coalescence is only slowed down because of the thermally-driven desorption of surfactant molecules. Both processes reversibly influence the long-term stability of foams.

This disadvantage has been overcome in recent years by the use of very small size surfactant-type solid particles, usually in the submicron range [BP Binks; TS Horozov, Angewandte Chemie, International Edition 2005, 44, (24), 3722-3725; A. Stocco; W. Drenckhan; E. Rio; D. Langevin; BP Binks, Soft Matter 2009, 5, (11), 2215-2222; AC Martinez; E. Rio; G. Delon; A. Saint-Jalmes; D. Langevin; BP Binks, Soft Matter 2008, 4, (7), 1531-1535]. Because of their size they will irreversibly adsorbed at the gas / liquid interface and form a solid-like reinforcement which completely protects the bubbles from dissolution and coalescence and stabilizes them for months or even years. However, these foams still lack a means by which their properties can be manipulated after their production. An object of the invention is to provide a material which allows the manipulation of a foam without compromising its stability.

An object of the invention are magnetic core-shell particles comprising a core of one or more magnetic metal oxides and a shell of silica, wherein the surface of the shell is partially silylated. "Partially silylated" is intended to mean that the surface of the silica shell comprises silanol groups Si-OH and silylated silanol groups Si-O-Si.

An indirect measure of the ratio of Si-O-Si groups to SiOH groups can be the carbon content as determined by elemental analysis, with high numbers indicating the ratio of Si-O-Si groups to SiOH groups. A preferred carbon content of the particles according to the invention is 0.1 to 10 wt .-%, particularly preferably 0.5 to 5 wt .-%, each based on the particle. As a direct measure of the ratio of Si-O-Si groups to SiOH groups, the residual content of reactive Silanol groups are determined on the surface. In the present invention, the method disclosed by J. Mathias and G. Wannemacher in the Journal of Colloid and Interface Science 125 (1988) is used by reaction with lithium aluminum hydride. This method involves reacting previously dried (100 ° C, 1 h, <10 ^"2 mbar), partially silylated, magnetic metal oxide particles, silica powder with a degassed solution of lithium aluminum hydride (2% by weight) in diglyme, measuring the pressure increase as a result hydrogen evolution, calculating the amount of hydrogen considering the volume of the lithium aluminum hydride solution, the volume of the vessel and the vapor pressure of the solvent, and calculating the density of the hydroxy groups according to the equation

4 = SiOH + LiAlH ₄ -> ^■ sSiO-Li + (= SiO) ₃ Al + 4 H ₂ . A preferred SiOH residual content of the particles according to the invention is 0.1 to 20 l / nm ² particle surface, particularly preferably 0.5 to 10 l / nm ² particle surface, in each case based on the particle. Preferably, the silylated silanol groups are those formed by reaction of hydroxy groups on the silica surface with organosilanes,

Organosilazanes, organosiloxanes or mixtures thereof are obtained.

The organosilanes are preferably selected from one or more of the following compounds:

(RO) ₃ Si (C _n H ₂ n + i) and (RO) ₃ Si (C _n H _2n -i) where R = alkyl, such as. Methyl, ethyl, n-propyl, isopropyl, butyl, and n = 1-20. Organosilanes R ' _x (RO) _y Si (C _n H ₂ n + i) and R' _x (RO) _y Si (C _n H _2n -i), wherein R = alkyl, such. Methyl, ethyl, n-propyl, isopropyl, butyl; R '= alkyl, such as. Methyl, ethyl, n-propyl, isopropyl, butyl; R '= cycloalkyl; n = 1-20; x + y = 3, x = 1, 2; y = 1, 2.

Haloorganosilanes X3 S 1 (C _n H _2n + i) and X3 S 1 (C _n H _2n-i), wherein X = Cl, Br; n = 1-20.

Halogenorganosilane X ₂ (R ') Si (C _n H _{2n +} i) and

X ₂ (R ') Si (C _n H _2n _i), where X = Cl, Br, R' = alkyl, such as. Methyl, ethyl, n-propyl, isopropyl, butyl; R '= cycloalkyl; n = 1-20.

Halogenorganosilane X (R ') ₂ Si ( _Cn H _{2n +} i) and

X (R ') ₂ Si (C _n H _2n _i) where X = Cl, Br; R '= alkyl, such as. Methyl, ethyl, n-propyl, isopropyl, butyl; R '= cycloalkyl; n = 1-20.

Organosilanes (RO) ₃ S 1 (CH ₂ ) _m -R ', wherein R = alkyl, such as. Methyl, ethyl, propyl; m = 0.1-20; R '= methyl, aryl, such as. B. -CeH _5, substituted phenyl radicals. Organosilanes (R ") _x (RO) _y Si (CH ₂ ) _m -R ', where R" = alkyl, x + y = 3; Cycloalkyl, x = 1, 2, y 1, 2; m = 0, 1 to 20; R '= methyl, aryl, such as. B. ΟδΗ ₅ , substituted phenyl. Halogenorganosilane X ₃ S 1 (CH ₂ ) _m -R ', where X = Cl, Br; m = 0.1-20; R '= methyl, aryl, such as. B. C6H5, substituted phenyl radicals.

Halogenorganosilane RX ₂ Si (CH ₂ ) _m R ', where X = Cl, Br; m = 0.1-20; R '= methyl, aryl, such as. B. C6H5, substituted phenyl radicals. Halogenorganosilane R ₂ XSi (CH ₂ ) _m R ', where X = Cl, Br; m = 0.1-20; R '= methyl, aryl, such as. As C ₆ H ₅ , substituted phenyl.

The organosilazanes are preferably selected from one or more of the following compounds:

R'R ₂ SiNHSiR ₂ R ', where R, R' = alkyl, vinyl, aryl.

The organosiloxanes are preferably selected from one or more of the following compounds:

Cyclic polysiloxanes D3, D4, D5 and their homologs, wherein D3, D4 and D5 are cyclic polysiloxanes having 3, 4 or 5 units of the type -O-Si (CH ₃ ) ₂ , for example octamethylcyclotetrasiloxane = D4.

Polysiloxanes or silicone oils of the type YO- [SiRR'-O] _m - [SiR '' R '''- O] _n ] _u - Y, where R = alkyl; R '= alkyl, aryl, H; R "= alkyl, aryl; R '''= alkyl, aryl, H; Y = CH ₃ , H, C _z H _{2z +} i with z = 1-20, m = 0, 1, 2, 3, ... 00, n = 0, 1, 2, 3, ... 00, u = 0, 1, 2, 3, ... 00, Si (CH ₃ ) ₃ , Si (CH ₃ ) ₂ H, Si (CH ₃ ) ₂ OH, Si (CH ₃ ) ₂ (OCH ₃ ), Si ( CH ₃ ) ₂ (C _z H _{2z + 1} ).

Specific examples are dimethyldiacetoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, dimethyldimethoxysilane, divinyltetramethyldisilazane, hexamethyldisilazane, methyltriacetoxysilane, methyltrichlorosilane, methyltriethoxysilane,

Methyltrimethoxysilane, octadecylmethyldichlorosilane, octadecyltrichlorosilane, octamethylcyclotetrasilazane, octylmethyldichlorosilane, octyltrichlorosilane, octyltriethoxysilane, octyltrimethoxysilane, phenyldimethylchlorosilane, phenyldimethylethoxysilane,

Phenyldimethylmethoxysilane, phenylmethyldichlorosilane, Phenylmethyldiethoxysilane, phenylmethyldimethoxysilane, phenyltrichlorosilane, phenyltriethoxysilane, phenyltrimethoxysilane, trimethylacetoxysilane, trimethylchlorosilane, trimethylethoxysilane, trimethylmethoxysilane, trimethylsilanol,

Vinyldimethylchlorosilane, vinyldimethylethoxysilane, vinyldimethylmethoxysilane, vinylmethyldichlorosilane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, vinyltrichlorosilane, vinyltriethoxysilane and vinyltrimethoxysilane, with octyltriethoxysilane and octyltrimethoxysilane being most preferred.

The core of the particles according to the invention may contain one or more oxides of iron, cobalt, nickel, chromium, europium, yttrium, samarium, gadolinium or mixed oxides thereof. In any case, the metal oxides may be present in the core in a uniform modification or in various modifications. The magnetic material of the core may further comprise mixed oxides comprising these metal oxides.

Also compounds of general formula ^XI M Fe ₂ 0 _4, wherein M ¹¹ is a metal component comprising at least two different divalent metals. Preferably, one of the divalent metals serving as the core may be manganese, zinc, magnesium, cobalt, copper, cadmium or nickel.

The core may also be composed of ternary systems of the general formula (M ^a ₁ - _x _ _y M ^b _x Fe _y) consist ^II Fe ₂ ^III 0 ₄ wherein M ^a and M ^{b are} the metals manganese, cobalt, nickel, zinc, copper, Magnesium, barium, yttrium, tin, lithium, cadmium, magnesium, calcium, strontium, titanium, chromium, vanadium, niobium or molybdenum, where x = 0.05 to 0.95, y = 0 to 0.95 and x + y <1. Specific examples are ZnFe ₂ 0 ₄ , MnFe ₂ 0 ₄ , Mn ₀ , ₆ Fe ₀ , ₄ Fe ₂ O ₄ , Mno, ₅ Zno, ₅ Fe ₂ 0 ₄ , Zno, iFei, g04, Zno, 2θ θι, 8O4, Zno, 3Fei, ₇ 0 ₄ , Zno, ₄ Fei, 60 ₄ and Mno, 39Zn ₀ , 27Fe2.340 ₄ , MgFe ₂ 0 ₃ , Mgi, ₂ Mn ₀ 2Fei, ₆ 0 ₄ ,

Mg ₁ , ₄ Mno, 4Fei, 20 ₄ , Mg !, ₆ Mn ₀ , ₆ Fe ₀ , ₈ 0 ₄ and Mg !, ₈ Mn ₀ , ₈ Fe ₀ , ₄ 0 ₄ . A preferred magnetic core is iron oxide comprising the iron oxides hematite, magnetite and maghemite. In a particular embodiment of the invention, the proportion of hematite, as determined from X-ray diffractograms, 1 to 10 wt .-%, preferably 4 to 8 wt .-%; Magnetite forms 20 to 50 wt .-%, preferably 35 to 40 wt .-%, and Maghämit forms 40 to 75 wt .-%, preferably 50 to 60 wt .-%, wherein the sum of the proportions is 100 wt .-% , In a further particular embodiment of the invention, the proportion of hematite is 5 to 40 wt .-%, preferably 10 to 30 wt .-%; Magnetite forms 50 to 90 wt .-%, preferably 60 to 85 wt .-%, and Maghämit forms 5 to 30 wt .-%, preferably 10 to 20 wt .-%, wherein the sum of the proportions is 100 wt .-% ,

The iron oxide polymorphs present in the core are crystalline and, in a preferred embodiment of the invention, have a hematite crystal size of 200 to 1200 angstroms, magnetite 200 to 600 angstroms and maghemite 150 to 500 angstroms, in all cases from Debye Calculated -Scherrer X-ray diffractograms.

The shell of the particles according to the invention comprises or consists essentially of silicon dioxide bearing hydroxyl groups on the surface. Preferably, the silica is an X-ray amorphous

Silica. "Essentially consists of" shall mean that small amounts, about 0.1 to 3% by weight, of a material other than silica are present, usually a compound or more with a bond between silica and the core material, for example, iron silicate.

The BET surface area of the magnetic core-shell particles is preferably 20 to 100 m ² / g, particularly preferably 30 to 60 m ² / g. The BET surface area is determined according to DIN ISO 9277.

In a preferred embodiment of the invention, the core-shell magnetic particles are mainly or exclusively present as aggregated metal oxide particles encased in silica. In general, the aggregate diameter is preferably not more than 250 nm, more preferably 30 to 200 nm.

In a further embodiment of the invention, the metal oxide content of the magnetic core-shell particles is 10 to 95 wt .-%, the silica content is 5 to 90 wt .-%. Preferably, the metal oxide content is 60 to 90 wt .-%, the silica content is 10 to 40 wt .-%. Another object of the invention is a dispersion comprising the magnetic core-shell particles. The content of the magnetic core-shell particles in the dispersion is preferably 0.1 to 50% by weight, more preferably 0.5 to 20% by weight, particularly preferably 2 to 10% by weight.

The liquid phase of the dispersion may comprise water and / or organic solvents, with the proviso that the liquid phase consists of one phase. Preferably, the liquid phase comprises water and one or more alcohols and / or diols. In the Typically, the content of alcohol and / or diol 5 to <50 vol .-%, preferably 10 to 40 vol .-%, particularly preferably 15 to 30 vol .-%. Specific examples are methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol and ethylene glycol.

In a particularly preferred embodiment of the invention, the dispersion is free of emulsifying surfactants.

Any method known to those skilled in the art can be used to prepare the dispersion. The methods include shaking the ingredients of the dispersion by hand to high shear mixing and selecting according to the intended use, the concentration of the dispersed particles, the viscosity and the stability of the dispersion.

A further object of the invention is the use of the magnetic core-shell particles or a dispersion comprising these particles, as a catalyst, in medical treatment or in adhesives. Examples

Example 1: Magnetic core-shell particles

Hydrophilic magnetic core-shell particles were prepared according to the method described in WO 2010/063557: a stream of a vaporous mixture of 0.49 kg / h of S1Cl ₄ and 0.05 kg / h of monosilane and a second stream in the form of an aerosol using a two-component nozzle and 5 m ³ (STP) / h nitrogen as a sputtering gas at room temperature (23 ° C) from a 25 wt .-% solution of iron (II) chloride, corresponding to 1.55 kg / h of iron (II) chloride, obtained in water, are introduced separately into the mixing zone of a reactor. This mixture is reacted in the combustion zone of the reactor in a flame generated by igniting a mixture of 7.9 m ³ (STP) / h of hydrogen and 21 m ³ (STP) / h of air. The residence time of the reaction mixture in the combustion zone is about 40 ms.

In the cooling zone following the combustion zone, the reaction mixture is cooled to 332 ° C by introducing 8 kg / h of water.

The resulting powder is separated on a filter from the gaseous substances. The hydrophilic powder comprises silica-coated iron oxide having a silica content of 19.3% by weight and an iron oxide content of 81.7% by weight comprising maghemite, hematite and magnetite phases in a ratio of 7: 7: 86.

Examples 2 to 6: Partially silylated magnetic core-shell particles

This powder is first filled into a mixer and atomized while being vigorously mixed with OCTMO. After the end of the sputtering, the mixing is continued for another 15 minutes, followed by heat treatment at 130 ° C for 4 hours to give partially silylated powders. Details are given in Table 1.

Table 1: Preparation of partially silylated, silica-coated iron oxide particles Example 2 3 4 5 6

OCTMO ¹ '10.0 7.5 5, 0 2.5 1.5

KohlenGew. -% 3.7 3, 0 2.0 1.1 0.7 substance

BET m ² / g 44 ± 2 45 ± 2 46 ± 2 52 ± 2 49 ± 2

SiOH 1 / nm ² 3, 08 3, 52 5.75 5.36 7.24

 ± 0.12 ± 0.14 ± 0.23 ± 0.21 ± 0.29

Parts octyltrimethoxysilane (OCTMO) / 100 parts oxide.

Example 7 Dispersions of Partially Silylated Magnetic Core Shell Particles

The partially silylated powder of Example 4 is dispersed in mixtures of water and ethanol and sonicated for 60 seconds using a Vibracell 75185 instrument with a 14 mm tip. The

Dispersions are kept closed to prevent the evaporation of ethanol. Dispersions containing 0.5, 2.0, 5.0, 10.0 and 20.0 g / l of partially silylated powder are prepared.

Example 8: Foams from the Dispersions of Partially Silylated Magnetic Core-Shell Particles Foams were prepared by handful shaking of the dispersions for 30 seconds, 9 ml each in a 30 ml vessel, to give a constant water / air ratio of f "= 0.3. The ethanol content is 5, 10, 20, 30 and 50 vol .-%. Ethanol concentration: The ethanol content has a significant influence on the formation of stable bubbles. Figure 2 shows a series of foams prepared at a constant particle concentration of 10 mg / ml (1% by weight) dispersed in a mixture of water with increasing ethanol concentrations of 5 to 50% by volume. Stable foams are obtained with ethanol contents of 10 to 30 vol.%, With 20 vol.% Being best. These foams are stabilized by the adsorption of magnetic particles at the interfaces of the bubbles. The formation of reinforced bubbles provides adequate protection against any type of destabilization, ie dissolving gas, coarsening and coalescing; in fact, no visible changes are detected after a period of 2 months. The bubbles are polydisperse with a range of sizes between 60 and 400 μιη. The stability of the foam is influenced by the wettability of the partially silylated powder. The wettability can be adjusted by the ethanol concentration of the dispersion. The wettability translates into the so-called wetting angle q, which forms a gas / liquid interface with the particle surface. Optimum foaming is generally expected at wetting angles of q »90 °. Since these wetting angles for the partially silylated particles can not be measured directly, they were approximated by measuring the contact angle of droplets of the same ethanol / water mixtures deposited on microscopic surfaces, either by pellets pressed from the partially silylated particles or a smooth surface of an octyltrimethoxysilane-coated glass flake, the silanating agent used to silylate the hydrophilic particles. On both surfaces, the contact angles are close to 90 °, the ideal condition for maximizing the adhesion of these particles to air / water interfaces.

Particle concentration: The concentration of partially silylated particles is varied between 0.5 and 20 mg / ml at a constant ethanol concentration of 20% by volume of the ethanol / water mixtures. It turns out that the concentration is directly related to the amount of foam produced. Increasing the particle concentration up to 50 mg / ml (5 wt%) will cause a substantial increase in foam height. At higher particle concentrations, a plateau of foam height appears to be achieved, and we assume that the viscosity of the dispersion increases in this region, making shaking foam generation more difficult.

Manipulation of Partially Silylated Particles Using Magnetic Fields and Field Gradients: Bubbles enveloped with the partially silylated particles can be easily moved or compacted using magnetic field gradients. These foams are remarkably stable under the influence of external magnetic forces and exhibit no sign of destruction under strong field gradients of 10 Tesla / m and even under a high field magnet of 65 Tesla / m (field of 14 Tesla).

Claims

claims 1. Magnetic core-shell particles, comprising a core of one or more magnetic metal oxides and a shell of silicon dioxide, characterized that the surface of the shell is partially silylated. 2. Magnetic core-shell particles according to claim 1, characterized, that the carbon content is 0.1 to 10 wt .-%. 3. Magnetic core-shell particles according to claims 1 or 2, characterized, the residual SiOH content of the particles is 0.1 to 20 l / nm ² particle surface area. 4. Magnetic core-shell particles according to Claims 1 to 3, characterized, the silylated silanol groups are those obtained by reacting hydroxy groups on the silica surface with organosilanes, Organosilazanes, organosiloxanes or mixtures thereof are obtained. 5. Magnetic core-shell particles according to claims 1 to 4, characterized, that the core comprises one or more iron oxides selected from the group consisting of hematite, magnetite and maghemite. 6. Magnetic core-shell particles according to claims 1 to 5, characterized, the BET surface area is 20 to 80 m ² / g. Magnetic core-shell particles according to claims 1 to 6, characterized, that they are present as an aggregate, wherein one or more metal oxides are coated by silica. 8. Magnetic core-shell particles according to claims 1 to 7, characterized, the metal oxide content is 10 to 95% by weight and the silica content is 5 to 90% by weight. A dispersion comprising the magnetic core-shell particles according to claims 1 to 8. 10. Dispersion according to claim 9, characterized, the content of the magnetic core-shell particles is 0.1 to 50% by weight. 11. Dispersion according to claims 9 or 10, characterized, the liquid phase is a solution comprising water and one or more alcohols and / or diols. 12. Dispersion according to claims 9 to 11, characterized, the content of alcohol and / or diol is 10 to <50% by volume. Dispersion according to claims 9 to characterized, that it is free of surfactants. 14. Use of the magnetic core-shell particles according to claims 1 to 8 or the dispersion according to claims 9 to 13 as a catalyst, in medical treatment and in adhesives.