CROSS REFERENCE TO RELATED APPLICATIONS: This application claims the benefit of U.S. Provisional Patent Application Serial No. 63/252,654 filed on 6 October 2021 under 35 U.S.C. §119 (e). U.S. Provisional Patent Application Serial No. 63/252,654 is hereby incorporated by reference.

FIELD:

This invention is directed toward dispersions including microcapsules comprising an oil core within a silicate outer shell dispersed within an alcohol-based continuous phase. While useful in a variety of personal care applications, the invention finds particularly utility in topical sanitizing formulations.

INTRODUCTION:

Aqueous silicone dispersions are useful in wide variety of applications including personal care. Such dispersions include both emulsions (i.e. liquid dispersed in a continuous liquid phase) and suspensions (i.e. solid dispersed in a continuous liquid phase). Surfactants (emulsifiers) are commonly used to facilitate both the formation and stability of such dispersions. Alcohol may also be included in some applications, (e.g. as a volatile solvent) but its addition can destabilize the dispersion particularly if added in sufficiently high quantities to provide a sanitizing effect (e.g. > 63 wt%). Depending upon the nature of the dispersion, destabilization may include sedimentation, flocculation and/or aggregation in suspensions and Ostwald ripening, phase separation and/or coalescence in emulsions. With respect to emulsions, stability can be improved by the addition of increasing quantities of surfactants, e.g. silicone polyethers (see US5770112 & US6410038) and/or by using high internal phase emulsions (“HIPEs”) (see US8840911). Unfortunately, the use increasing quantities of surfactants can make the resulting emulsion unsuitable for many applications, e.g. personal care formulations where high levels of surfactant may irritate the skin and/or interfere with other constituents of the formulation. Similarly, alkoxylated surfactants are being phased out due to growing concerns regarding trace impurities and/or undesired sensory effects (e.g. tackiness).

The use of so-called “pickering emulsions” can reduce the quantity of surfactant required to form stable oil-in-water emulsions. Pickering emulsions utilize discrete solid particles (e.g. silica, starch, cellulose, chitosan, etc.) to stabilize droplets of the oil phase within the continuous water phase. In particular, the solid particles assemble about the outer circumference of individual oil droplets at the interface with the continuous phase. See for example: US2015/0125498, US2004/0241120, EP2782546 and EP3656444. However, even pickering emulsions become less stable with increasing alcohol content, e.g. greater than 50 wt%. Moreover, the stability of the emulsion is highly dependent upon the composition, wettability, adsorption, concentration, size, shape and surface charge of the solid particle utilized along with the selection of oil and continuous phases. See: Albert, et. al., Preparation Processes, Key Parameters Governing Their Properties and Potential for Pharmaceutical Applications, Journal of Controlled Release 309 (2019), 302-332. These factors along the additional particle handling steps have limited the use of pickering emulsions. Additionally, pickering emulsions utilize relatively high weight ratios of particles (e.g. silica) to oil which leads to undesirable sensory effects.

Thus, there remains an unmet need for stable, alcohol-based, oil containing dispersions and in particularly, those that are lower cost and/or simpler to prepare.

SUMMARY:

Aqueous-based suspensions of silicate shell microcapsules including a silicone or organic oil core are well known. See for example: EP1471995, US8435559, US9005639, US9089830, US9192549 and US9758431 - all of which share an inventor with the present invention. To the surprise of the present inventor, these aqueous-based suspensions remain stable even after being converted to alcohol-based suspensions, e.g., by the post-addition of alcohol to make up over 50 wt% of the suspension. It is noteworthy that recovery of the aforementioned silicate shell microcapsules from an aqueous suspension via liquid removal techniques (e.g., spray drying) followed by redispersion in an organic solvent (e.g., ethanol) was unsuccessful, i.e., the spay dried microparticles could not be dispersed and immediately separated out of the solution and formed unacceptably large aggregated particles, e.g., particle sizes of greater than 500 pm which create an undesirable sensory effect. (See example 6).

The microcapsules of the present invention provide a silicate shell comprising a continuous solid network about an oil phase core rather than a loose assembly of discrete solid particles located about the core as provided in pickering emulsions. Consequently, the present shell provides improved core integrity while avoiding the added complexity of particle selection, handling and mixing associated with pickering emulsions or the use of excessive quantities and/or expense of surfactants associated with traditional alcohol-based emulsions.

In one aspect, the present invention includes an alcohol-based suspension of microcapsules wherein the microcapsules comprise a shell comprising a continuous network of silicate about a core of oil. In another aspect, the invention includes a method for making the aforementioned alcohol-based suspension. In yet another aspect, the invention includes a personal care product such as a topical sanitizer which incorporates the subject alcohol-based suspension. Many embodiments are described.

DETAILED DESCRIPTION:

As used herein, the term “dispersion” refers to both emulsions, (i.e., a liquid dispersed phase within a liquid continuous phase) and suspensions, (i.e., a solid dispersed phase within a liquid continuous phase). While the present invention may utilize aqueous silicone emulsions as an intermediate step of preparation, the present invention is directed toward alcohol-based suspensions. As used herein, the term “alcohol-based” means that more than 50 wt% of the suspension comprises alcohol. In several embodiments, the present suspensions comprise at least: 60 wt%, 63 wt%, 65 wt%, 70wt%, 75 wt%, 80 wt%, 85wt% and even 89 wt% of alcohol. The selection of alcohol will typically depend upon the intended application; however, Ci-Ce monohydric alcohols such as: methanol, ethanol, n-propanol, isopropanol, butanol, t-butanol, 2-butanol, pentanol, hexanol and combinations thereof are generally preferred. In a sub-class of embodiments, C2-C4 monohydric alcohols are preferred such as: ethanol, 1 -propanol and 2-propanol and combinations thereof. The remaining proportion of the continuous phase preferably comprises water, e.g., at least 10 wt%, 15 wt% or even 20 wt% of the total weight of the suspension comprises water. In alternative embodiments, the continuous phase comprises from 10 to 39 wt% water, 10 to 35 wt% water or 15 to 30 wt% water. As will be described below, water present in the subject suspension may be residual water remaining from a preceding step in the preparation of the subject suspensions.

The subject alcohol -based suspensions include at least 1, 2, 5 and in some embodiments at least 10 wt% of microcapsules. In other embodiments, the subject suspensions include from 1 to 30 and more preferably from 10 to 30 wt% of microcapsules. The microcapsules preferably have a mean average particle size (D(v0.5)) of from 0.3 to 200 pm, and more preferably from 1 to 20 pm. The microcapsules include a core comprising an oil and a shell comprising a continuous network of silicate about (i.e., circumferentially around) the core. Such microcapsules along with corresponding methods of preparation and characterization are described in: EP1471995, US8435559, US9005639, US9089830, US9192549 and US9758431, each of which is incorporated herein in its entirety. As per the methods described in the preceding references, aqueous suspensions of silicate shell microcapsules may be formed and as part of the subject invention followed by the addition of alcohol until the desired final alcohol content is obtained. This addition of alcohol may occur with mixing at room temperature. In an alternative embodiment, a portion of the water may be removed from the aqueous suspension prior to the addition of alcohol. However, when removing water from such suspensions prior to addition of alcohol, the remaining quantity of water should be enough to maintain a suspension and avoid agglomeration of the silicate shell microcapsules and to result in a final suspension comprising at least 10 wt% water.

As will be described, additional constituents may be included in the suspension, including to either or both the alcohol-based continuous phase and/or the core the microcapsules (dispersed phase). The selection of such additives will depend upon the intended end use. For personal care applications, representative additives include emollients, humectants, vitamins, thickeners, preservatives, antimicrobials, oxidants (H2O2), fragrances, sunscreens, etc. The subject suspensions may be formulated in a variety of formats including liquids, sprays, gels, creams, pastes, lotions, etc.

The core of the microcapsules includes an oil. As used herein, the term “oil” refers to a hydrophobic liquid which is immiscible with the continuous phase. Applicable oils include hydrocarbon-based oils of a mineral, vegetable or synthetic origin, e.g., paraffin oil, hydrogenated isoparaffin, hydrogenated liquid polydecene, petrolatum, olive oil, linseed oil, shea butter. The term “oil” also includes silicones. Representative silicones include both volatile and non-volatile species along with both cyclic, linear and branched species. Representative volatile cyclic species include: octamethylcyclotetrasiloxane, decamethyl-cyclopentasiloxane and dodecyl-methylcyclohexasiloxane. Representative volatile linear species include: hexamethyl disiloxane and decamethyltetrasiloxane. Representative classes include: polyalkylsiloxanes, polyaryl siloxanes, polyalkylarylsiloxanes, polysiloxane gums, polysiloxane elastomers and combinations thereof. A preferred group include DOWSIL™ 200 fluids (polydimethylsiloxane) including those having viscosities from about 5 to about 30 cSt (centistokes) measured at 25°C according to ASTM D4283-98 (2015). In yet another embodiment, the silicone(s) used to prepare the core are non-reactive with other constituents of the subject suspension. In this context, the term “non-reactive silicone” means that the silicone(s) does not include functional groups that chemically react (i.e., break or form covalent bonds) with those of other constituents of the suspension under the conditions used to prepare the suspension. For reference, examples of reactive species include those with functional groups that undergo hydrosilylation (e.g. - SiH, -SiVinyl), condensation (e.g. -SiOH) or hydrolysis reactions with other constituents of the suspension under the conditions used to prepare the suspension.

The shell of the microcapsules comprising a continuous network of silicate about the core. As used herein, the term “silicate” means a networked polymer including repeating units selected from at least one of: SiCh/z and RSiOs/z, where R is selected from: hydrogen, or alkyl, aryl or alkoxyl (including from 1 to 6 carbon atoms. In preferred embodiments, the silicate is predominantly (e.g., >75, 90 or even 100 wt%) comprised of repeating units represented by: SiOi/z. As will be subsequently described, the shell is preferably formed about the core by an emulsion polymerization (hydrolysis and condensation) of a tetraalkoxysilane along with other optional water reactive silicon containing compounds in water and in the presence of one or more of a cationic or amphoteric surfactant and optional catalyst (e.g., organo tin compound). The shell preferably has a thickness of from 10 nm to 50 nm as measured by the technique described below.

The subject alcohol-based suspensions may be prepared according to the following steps: i) preparing an aqueous emulsion by combining an oil and a cationic surfactant in water to form a dispersed phase of oil droplets within a continuous phase of water, ii) preparing an aqueous suspension of microcapsules by adding a water reactive silicon compound comprising tetraalkoxysilane to the aqueous emulsion of step i) which reacts to form a shell comprising a continuous network of silicate about said oil droplets, iii) preparing an alcohol-based suspension by adding a sufficient quantity of alcohol to the aqueous suspension of step ii) to form a suspension comprising at least 60 wt % alcohol based upon the total weight of the suspension.

In further regarding to step i), an aqueous emulsion of the oil (oil-in-water) may be prepared by combining an oil along with a cationic surfactant in water to form a dispersed phase of oil droplets within a continuous phase of water. As used herein, the term “cationic surfactant” means a surfactant including a functional group having a positive charge, e.g., quaternary ammonia compounds with positively charged surface-active moieties. This definition includes amphoteric surfactants which have both positive and negatively charged groups but excludes non-ionic and anionic surfactants. Cationic surfactants useful in this invention include quaternary ammonium hydroxides such as octyl trimethyl ammonium hydroxide, dodecyl trimethyl ammonium hydroxide, hexadecyl trimethyl ammonium hydroxide, octyl dimethyl benzyl ammonium hydroxide, decyl dimethyl benzyl ammonium hydroxide, didodecyl dimethyl ammonium hydroxide, dioctadecyl dimethyl ammonium hydroxide, tallow trimethyl ammonium hydroxide and coco trimethyl ammonium hydroxide as well as corresponding salts of these materials, fatty amines and fatty acid amides and their derivatives, basic pyridinium compounds, quaternary ammonium bases of benzimidazolines and polypropanolpolyethanol amines but is not limited to this list of cationic surfactants. Alternatively, the cationic surfactant may be cetyl trimethyl ammonium chloride. In yet another alternative embodiment, the cationic surfactant may be selected from amphoteric surfactants such as: cocamidopropyl betaine, cocamidopropyl hydroxy sulfate, cocobetaine, sodium cocoamidoacetate, cocodimethyl betaine, N-coco-3-aminobutyric acid and imidazolinium carboxyl compounds but is not limited to this list of amphoteric surfactants. These aforementioned surfactants may be used individually or in combination. The surfactant may be combined with water and the resulting aqueous solution used as a component in an aqueous continuous phase. The concentration of the cationic surfactant during the formation of the oil in water emulsion is preferably between 0.1% and 0.3% by weight of the entire oil phase. The aqueous phase may contain additional/optional components including thickeners, preservatives, antimicrobials and water-soluble actives and fragrances.

The oil phase and aqueous phase including the surfactant are mixed to form an oil in water emulsion. Mixing and emulsion formation may occur using any known techniques in the emulsion art. Typically, the oil phase and aqueous solution of the surfactant are combined using simple stirring techniques to form an emulsion. The particle size of the oil in water emulsion may then be reduced prior to shell formation described below. Representative mixing devices include homogenizers, sonolators, rotor-stator turbines, colloid mills, microfluidizers, blades, helix and combination thereof. This further processing step reduces the particle (droplet) size of the starting cationic oil in water emulsion to values ranging from 0.2 to 200 pm.

The weight ratio of oil phase to aqueous phase in the emulsion can generally be between 40:1 and 1 :50. More preferably, the weight ratio of oil phase to aqueous phase is between 2:1 and 1:3. If the oil phase composition is highly viscous, a phase inversion process can be used in which the oil phase is mixed with surfactant and a small amount of water, for example 2.5 to 10.0% by weight based on the oil phase, forming a water-in-oil emulsion which inverts to an oil-in-water emulsion when sheared.

In step ii) an aqueous suspension of microcapsules may be prepared by adding a water reactive silicon compound comprising tetraalkoxysilane to the aqueous emulsion of step i). While not wishing to be bound by theory, it is believed step ii) effects an “ex-situ emulsion polymerization” by which the tetraalkoxysilane precursors hydrolyzes and condenses at the oil/water interface forming a continuous network of silicate about the oil droplets and resulting in core-shell microcapsules. The tetraalkoxysilane, such as tetraethoxy silane (TEOS), can be used in monomeric form or as a liquid partial condensate. The tetraalkoxysilane can be used in conjunction with one or more other water- reactive silicon compound having at least two, preferably at least 3, Si — OH groups or hydrolysable groups bonded to silicon, for example an alkyltrialkoxysilane such as methyltrimethoxysilane or a liquid condensate of an alkyltrialkoxysilane. Hydrolysable groups can for example be alkoxy or acyloxy groups bonded to silicon. The water reactive silicon compound can for example comprise 75 to 100 wt% tetraalkoxysilane and 0 to 25 wt% trialkoxysilane. The alkyl and alkoxy groups of the tetraalkoxysilanes or other silanes preferably contain 1 to 4 carbon atoms, most preferably 1 or 2 carbon atoms. The tetraalkoxysilane and other water-reactive silicon compound if used, hydrolyses and condenses to form a network polymer comprising a 3-dimensional network of silicon-based material, around the emulsified droplets of the lipophilic active material composition. The water-reactive silicon compound preferably comprises at least 75 wt%, and most preferably 90-100 wt% tetraalkoxy silane. The tetraalkoxysilane and other water reactive silicon compound if used, can be added to the emulsion as an undiluted liquid or as a solution in an organic solvent or in an emulsion form. The tetraalkoxysilane and the oil in water emulsion are mixed during addition and subsequent polymerization to form the silicon-based polymer shell on the surface of the emulsified droplets. Mixing is typically affected with stirring techniques. Common stirring techniques are sufficient to maintain the particle size of the starting oil in water emulsion while allowing the tetraalkoxysilane to polymerize and condense at the oil water interface. The amount (based on weight) of tetraalkoxysilane added in step II preferably ranges from 6/1 to 1/13, or alternatively from 1/3.6 to 1/6.1, based on the weight amount of oil phase present in the emulsion. The polymerization of the tetraalkoxysilane at the oil/water interface is preferably a condensation reaction which may be conducted at acidic, neutral or basic pH. The condensation reaction may be carried out at ambient temperature and pressure, but can be carried out at increased temperature, for example up to 95°C and increased or decreased pressure, for example under vacuum.

Any catalyst known to promote the polymerization of the tetraalkoxysilane may be added to form the shell of the microcapsule. The catalyst is preferably an oil soluble organic metal compound, for example an organic tin compound, particularly an organotin compound such as a diorganotin diester, for example dimethyl tin di(neodecanoate), dibutyl tin dilaurate or dibutyl tin diacetate, or alternatively a tin carboxylate such as stannous octoate, or an organic titanium compound such as tetrabutyl titanate. An organotin catalyst can for example be used at 0.05 to 2% by weight based on the tetraalkoxysilane. An organotin catalyst has the advantage of effective catalysis at neutral pH. The catalyst is preferably mixed with the oil phase components before it is emulsified as this promotes condensation of the tetraalkoxysilane at the surface of the emulsified oil phase droplets. A catalyst may alternatively be added to the emulsion before the addition, simultaneously with, or after the addition of the tetraalkoxysilane. Encapsulation can however be achieved without catalyst. The catalyst, when used, can be added undiluted, or as a solution in an organic solvent such as a hydrocarbon, alcohol or ketone, or as a multiphasic system such as an emulsion or suspension.

The polymerization reaction in step ii) is allowed to proceed so as to form the shell of a microcapsule that is at least 10 nanometers thick, alternatively the shell has a thickness in the range of 10 to 50 nm. Shell thicknesses may be determined from the mean average particle size (PS) of the resulting microcapsules in suspension and the amounts of the oil phase and tetraalkoxysilane used in the process to prepare them according to the following formula:

Shell thickness (nm) = [(PS/2)-(PS/2)*Payload/100) ^1/3 ]*1000 where:

PS is the mean average particle size (Dv 0.5) expressed in micrometers.

Payload = volume of oil phase *100/( volume of oil phase + volume of shell).

Volume of oil phase = mass of oil phase/density of oil phase.

Volume of shell = mass of shell/density of shell.

This equation is based on the spherically shaped microcapsules having an average diameter as determined by their average volume particle (droplet) size distribution (Dv50) as measured by laser diffraction technique using a Mastersizer 3000 with a Hydro SV attachment (Malvern Panalytical - a division of Spectris, Egham, Surrey, UK). Thus, the shell thickness is the difference between the radius of the microcapsule and the radius of the core material in the microcapsule.

Shell thickness where:

Payload represents the percentage of the microcapsule occupied by the core material, e.g. oil phase, as determined by the amount of oil phase present in the emulsion. Thus, payload is calculated by the formula:

Payload = volume of oil phase* 100/(volume of oil phase + volume of shell)

The volume of oil phase equals the mass of oil phase divided by the density of oil phase. The mass of the oil phase in this equation is the same as the amount used in the process (as per step i) to prepare the microcapsules. The volume of the shell equals mass of shell divided by the density of silica. The silicate comprising the shell is expected to have an average chemical composition with the empirical formula SiOj. Thus, the density of the shell is estimated to be 2 g/mL, which approximates the density of silica (SiOz). The mass of the shell is calculated from the amount of tetraalkoxysilane added to the process (as per step ii). More specifically, the mass of the shell is based on the expected stoichiometric yield of silicate of empirical formula SiOz given the type and amount of the tetraalkoxysilane used in the process. In one embodiment, the tetraalkoxysilane is tetraethoxysilane (TEOS) having a density of 0.934 g/mL. In this embodiment, the assumed complete hydrolysis and condensation of 1 g of TEOS produces 0.288 g of SiOz polymer (silicate).

In step iii), an alcohol-based suspension is prepared by adding a quantity of alcohol to the aqueous suspension of step ii) to form a suspension comprising more than 50 wt % alcohol based upon the total weight of the suspension. In many embodiments, the present suspensions comprise at least: 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85wt% and even 89 wt% of alcohol.

As mentioned, additional additives may be included in the dispersed oil phase or continuous aqueous phase during the preparation of the emulsion in step i). In order to be included within the oil phase, the additive should be immiscible to readily form a dispersed phase within the aqueous continuous phase. While the cores of the suspension may have uniform compositions, it is also possible to prepare cores having different compositions, e.g., silicone oil rich droplets and organic oil rich droplets.

When used in personal care applications such as topical sanitizers (i.e. products commonly including > 65 wt% alcohol), it may be desirable to further include a humectant and/or additional emollient. That is, even though the oil may serve as an emollient, there may be a desire to include additional constituents to further moisturize and protect skin from the drying effect of alcohol. Representative examples of humectants include glycerin, glycerin derivatives, sodium hyaluronate, hyaluronic acid, betaine, amino acids, glycosaminoglycans, honey, sorbitol, glycols such as propylene glycol, polyols, sugars, hydrogenated starch hydrolysates, lactic acid, lactates, urea, and the like. A particularly preferred humectant is glycerin. Representative examples of emollients include the aforementioned oils, i.e. oils such as petrolatum based oils, petrolatum, vegetable based oils, mineral oils, natural or synthetic oils, lanolin and its derivatives along with fatty esters, glycerol esters and derivatives, propylene glycol esters and derivatives, alkoxylated carboxylic acids, alkoxylated alcohols, fatty alcohols, fatty acids, and combinations thereof. A particularly preferred emollient is petrolatum. The suspension of the present invention may include one or more emollient and/or humectant (in addition to said oil) in an amount of from about 0 wt% to about 20% wt% of the suspension.

In many embodiments it will be desirable to reduce or eliminate various constituents from the subject suspension including one or more, or all of the following: i) non-ionic (including alkoxylates such as silicone polyethers) surfactants ii) reactive silicones (as previously defined), and/or iii) solid particles (e.g., silica, cellulose, starch) in contrast to the subject core/shell microcapsules.

In selected embodiments, the subject emulsions are substantially free of one or more, or all of the preceding constituents. In this context, the term “substantially free” means less than 1 wt%, preferably less 0.5 wt% and more preferably less than 0.1 wt% and still more preferably less than 0.01 wt%, based upon the total weight of the suspension. In further regard to personal care applications such as hand sanitizers, it may be preferred to include less than 1 wt% of total surfactant in the suspension.

In a preferred embodiment, the subject alcohol-based suspension of microcapsules are sufficiently stable so as to have a turbidity (NTU) of at least 25 as determined by ISO 15715 (2003) after being stored for six days at room temperature (20°C) at standard pressure (1 atm or 760 mm Hg).

Unless otherwise stated, particles size measurements are determined by laser diffraction using a Mastersizer 2000 from Malvern Instruments Ltd., UK. Unless otherwise stated, all particle sizes indicated herein are mean average particle size according to D(v0.5).

Many embodiments of the invention have been described and, in some instances, certain embodiments, selections, ranges, constituents, or other features have been characterized as being “preferred.” Such designations of “preferred” features should in no way be interpreted as an essential or critical aspect of the invention. Expressed ranges specifically include designated end points.

EXAMPLES:

To better illustrate the invention, a series of alcohol-based suspension of microcapsules were prepared using different oils, in either ethanol or propanol. In each of Examples 1 through 4, 60g of the identified oil was emulsified in 138g demineralized water containing 0.58g hexadecyltrimethylammonium chloride cationic surfactant and 0.08g hydrogen chloride (IN). (In Examples 2 and 4, the oil and demineralized water were first heated to 70°C). The coarse emulsion was further emulsified with a Ika® Ultra-Turrax Basic 25 mixer at 10000 rpm for 2 minutes. 10.04g TEOS (tetraethylorthosilicate) was added to the emulsion while stirring to form after TEOS hydrolysis and condensation a suspension of oil containing core-silica shell core-shell microcapsules. The obtained suspension was added to a hydro-alcoholic solution (ethanol or isopropanol) containing at least 10 wt% water. The stability of the microcapsules in the resulting alcohol-based suspension was measured by turbidimetry via ISO 15715 (2003), upon formation (TO) and after being stored for six days. Unless otherwise indicated, all preparation and testing were conducted at room temperature (RT) at standard pressure (1 atm or 760 mm Hg).

Example 1 : Mineral oil:

Example 2: Petrolatum/Mineral oil/polydimethylsiloxane 2 cPs (4/1/5 mix (w/w))

Example 3: Lindseed oil

Example 4: Shea butter

Example 5: Comparison with Pickering emulsion

An alcohol-based suspension of microcapsules was prepared according to the same methodology of Example 1 except with the addition of ethanol to obtain a suspension comprising 63 wt% ethanol. Prior to the addition of ethanol, the suspension had an average volume particle size distribution (Dv50) of 7.53 pm. After the addition of ethanol, the average volume particle size (Dv50) was 8.49 pm, indicating that the suspension remained stable after the addition of ethanol.

A similar Pickering emulsion was prepared according to the following methodology. 2.63g of a continuous water-based phase was prepared by dispersing 2.63g of silica (Aerosil™ 200 from Evonik) in 97.37g of demineralized water. 4g of mineral oil was emulsified in 8g of the continuous water-based phase with the assistance of a Ika® Ultra-Turrax Basic 25 mixer at 10000 rpm for 2 minutes. A monodispersed Pickering mineral oil-in-water emulsion having average volume particle size distribution (Dv50) of 29.7pm was obtained. The resulting emulsion was then added to a hydroalcoholic solution to obtain a 63 wt% ethanol emulsion. The Pickering emulsion immediately broke up with a significant increase of the average volume particle size distribution (Dv50), i.e., 67.6pm - indicating that the suspension became unstable after the addition of ethanol. Additional silica (2.63g) was then added to the Picking emulsion. No improvement in stabilization was observed.

Example 6: Comparison with Spray-dried microcapsules

The microcapsule suspension obtained in example 1 was spray-dried in a Niro® spray-drier using a rotary nozzle at a pressure of 8 bars and an inlet temperature of 100°C. The resulting microcapsule powder was then added to a hydro-alcoholic solution at 63 wt% ethanol. The powder would not disperse and immediately separate out of the solution. A stable suspension could not be formed.