WO2024256601A1 - Simple emulsions - Google Patents

Abstract

The invention relates to a process for producing a stable emulsion not comprising a surfactant.

Description

SIMPLE EMULSIONS

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing a simple water-in-oil emulsion not comprising a surfactant.

STATE OF THE ART

In the prior art, emulsion systems commonly require the use of surfactants to be stabilized, these surfactants having the disadvantage of being able to bring contaminants into the phases. In addition, surfactants in emulsions pose significant environmental problems, and the successive steps involved in emulsion manufacturing processes result in significant energy costs and process complexity, which reduces the key performance indicator of yield/time.

Therefore, the present invention aims to provide a method for manufacturing a simple water-in-oil emulsion not comprising a surfactant and in which the volume fraction of aqueous phase is large.

The inventors of the present invention have surprisingly discovered that certain characteristics between the aqueous phase and the oily phase of a simple water-in-oil emulsion make it possible to obtain a particularly stable simple water-in-oil emulsion comprising a significant volume fraction of aqueous phase, even in the absence of surfactant.

SUMMARY

The present invention relates to a method for manufacturing a simple water-in-oil emulsion comprising a step of adding dropwise an aqueous phase to an oily phase, said oily phase being amphiphilic, said emulsion not comprising surfactant, in which an adhesion energy is present between two droplets of aqueous phase dispersed in the oily phase, preferably the adhesion energy between two droplets of dispersed aqueous phase is from 10' ⁵ J.nT ² to 10' ³ J.nT ² .

Advantageously, the oily phase comprises at least one oil chosen from the group consisting of: silicone oils, poly(acrylate) oil, poly(ester) oil, mineral oils, vegetable oils and their mixtures, preferably F at least one oil is chosen from the group consisting of: silicone oils, poly(acrylate) oil, poly(ester) oil, and their mixtures.

Advantageously, the oily phase comprises at least one silicone oil, preferably a silicone oil selected from the group consisting of: poly(dimethylsiloxane) (PDMS), poly(monomethylsiloxane) (PPMS), hydroxy terminated poly(dimethylsiloxane) (PDMS-OH) and mixtures thereof, preferably the silicone oil is hydroxy terminated poly(dimethylsiloxane) (PDMS-OH).

Advantageously, the aqueous phase comprises at least one of: glycerol, poly(ethylene glycol), and alginate and mixtures thereof, preferably the aqueous phase comprises glycerol.

Advantageously, the dropwise addition of the aqueous phase to the oily phase is carried out at a flow rate of 0.001 mL.s' ¹ to 50 mL.s' ¹ , preferably of 0.001 mL.s' ¹ to 20 mL.s' ¹ , more preferably of 0.001 mL.s' ¹ to 10 mL.s' ¹ , even more preferably of 0.001 mL.s' ¹ to 0.2 mL.s' ¹ , better still of 0.001 mL.s' ¹ to 0.05 mL.s' ¹ , even better still of approximately 0.01 mL.s' ¹ .

Advantageously, the mixture comprising the aqueous phase and the oily phase is continuously stirred, preferably at a stirring speed ranging from 100 rpm to 3000 rpm, more preferably at a stirring speed ranging from 500 rpm to 2500 rpm.

Advantageously, the shear rate applied during stirring is from 1000 s' ¹ to 4000 s' ¹ , preferably from 2000 s' ¹ to 3000 s' ¹ . Advantageously, the ratio between the dynamic viscosity of the aqueous phase and the dynamic viscosity of the oily phase is from 0.01 to 20, preferably from 0.01 to 10, more preferably from 0.1 to 10, even more preferably from 1 to 10, the dynamic viscosities being measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter cone, an angle of 2 degrees and a temperature control cell set at 25 °C.

Advantageously, the interfacial tension y between the aqueous phase and the oily phase is from 0 J.m' ² to 50xl0' ³ J.m' ² , preferably from 20xl0' ³ J.nT ² to 40xl0' ³ J.nT ² .

DEFINITIONS

In the present invention, the terms below are defined as follows:

"Adhesion" refers to the ability of suspended particles or droplets to stick together when in close proximity. When two droplets come into close contact, their surface may deform, resulting in a contact angle 9 between them. Adhesion may therefore also be described as "wetting". Adhesion occurs in systems where there is an attractive interaction between the two W/O interfaces. This interaction may be attributed to intermolecular forces, chain entanglements, or both, across the interfaces. Adhesion in a system of aqueous droplets suspended in an external oil phase may be characterized quantitatively by measuring an "adhesion energy". Advantageously, the adhesion energy E may be calculated by the formula

[Math 1]

E = 2y(l — cos 0) where y is the interfacial tension between the oil phase and the aqueous phase and θ is the contact angle between the droplets. θ can be measured by different techniques depending on its value. When θ>30°, it can be obtained by direct microscopic measurement and image analysis techniques with geometric estimation. When 9<30°, it is obtained by observing the oil film between the adherent droplets according to the formula

dans laquelle Rfiim est le rayon du film d'huile et R_g\ et R_g sont les rayons des gouttelettes. Dans ce cas particulier, en raison de sa faible réflectivité, le film peut être observé au microscope optique ou confocal. Le « test d'adhésion avec une aspiration par micropipette » désigne un exemple de méthode de détermination de l'adhésion entre deux gouttes, la méthode comprenant l'utilisation d'une aspiration par micropipette pour le test d'adhésion tel que représenté dans la Figure 1, permettant la détermination précise de la taille du film d'huile à l'aide d'un microscope confocal. [Math 2]

where Rfiim is the radius of the oil film and R _g \ and R _g are the radii of the droplets. In this particular case, due to its low reflectivity, the film can be observed under an optical or confocal microscope. "Adhesion test with micropipette aspiration" refers to an example of a method for determining adhesion between two drops, the method comprising the use of micropipette aspiration for the adhesion test as shown in Figure 1, allowing the precise determination of the size of the oil film using a confocal microscope.

The adhesion energy can be measured by any method known to those skilled in the art. There are many methods for measuring the adhesion energy and the resulting value is independent of the measurement method. For example, the adhesion energy can be measured by a method selected from the group consisting of the method described in Poulin et al, Phys. Rev. Lett. 77:3248, 1996, the method described in Poulin et al, Phys. Rev. Lett. 79:4862, 1997, and the adhesion test method (consisting of using an adhesion test with micropipette aspiration and the formula:

[Math 1]

E = 2y(l — cos 0))

"Active agent" or "active ingredient" means a substance that has an effect, in particular in a field selected from the group consisting of therapeutic, cosmetic, agricultural, maintenance, chemical products, paints, fuels, lubricants, bitumens and drilling muds. The active agent may be a chemical or biological substance. Preferably, the active agent is a chemical substance.

Advantageously, the active agent is chosen from the group consisting of: - a crosslinker other than the possible crosslinking agent of the aqueous phase or the oily phase (i.e. which cannot cause crosslinking of the oligomers and/or monomers of the aqueous phase), a hardener, a curing agent (such as a urea derivative), a curing agent accelerator (such as amide, amine and imidazole derivatives), an organic or metallic catalyst (such as an organometallic or inorganometallic complex of platinum, palladium, titanium, molybdenum, copper, zinc or salts of metal complexes dissolved in polyethylene glycol or polyethylene glycol derivatives) used to polymerize formulations of polymers, elastomers, rubber, paints, adhesives, sealants, mortars, varnishes or coatings;

- a colorant or pigment used in the formulations of elastomers, paints, coatings, adhesives, sealants, mortars or papers;

- a fragrance (as defined by the International Fragrance Association (IFRA) list of molecules available at www.ifraorg.org) intended for use in detergents such as laundry detergents, cleaning products, cosmetics and personal care products, textiles, paints, coatings;

- a flavor, a vitamin, an amino acid, a protein, a lipid, a probiotic, an antioxidant, a pH regulator, a preservative for food compounds and animal feed;

- a plant extract or essential oil derivative such as propolis extract, menthol derivatives or poppy petal extract for personal care formulations;

- a softener, moisturizer, conditioner for detergents, laundry detergents, cosmetics and personal care products. In this regard, active ingredients that can be used are, for example, listed in US Patents 6,335,315 and US Patents 5,877,145;

- an anti-coloration agent (such as an ammonium derivative), an antifoaming agent (such as an alcohol ethoxylate, an alkylbenzene sulfonate, a polyethylene ethoxylate, an alkyl ethoxysulfate or an alkyl sulfate) for detergents and laundry and household care products;

- a lightening agent, also known as a color activator (such as a stilbene derivative, a coumarin derivative, a pyrazoline derivative, a benzoxazole or a naphthalimide derivative) for use in detergents, laundry products, cosmetics and personal care products;

- a biologically active compound such as an enzyme, a vitamin, a protein, a plant extract, an emollient agent, a disinfectant agent, an antibacterial agent, an anti-UV agent, a drug intended for cosmetic and personal care products, and textiles. Among these biologically active compounds, we can cite: vitamins A, B, C, D and E, para-aminobenzoic acid, alpha-hydroxy acids (such as glycolic acid, lactic acid, malic acid, tartaric acid or citric acid), camphor, ceramides, polyphenols (such as flavonoids, phenolic acid, ellagic acid, tocopherol, ubiquinol), hydroquinone, hyaluronic acid, isopropyl isostearate, isopropyl palmitate, oxybenzone, panthenol, proline, retinol, retinyl palmitate, salicylic acid, sorbic acid, sorbitol, triclosan, tyrosine;

- a disinfectant, an antibacterial agent, an anti-UV agent, for paints and coatings;

- a fertilizer, herbicide, insecticide, pesticide, fungicide, repellent or disinfectant for agrochemicals;

- a flame retardant (such as a brominated polyol such as tetrabromobisphenol A, a halogenated or non-halogenated organophosphorus compound, a chlorine compound, an ammonium polyphosphate, an aluminium trihydrate, an antimony oxide, a zinc borate, a red phosphorus, a melamine or a magnesium dihydroxide) intended for use in plastics, coatings, paints and textiles;

- a photonic crystal or photochromophore for use in paints, coatings and polymeric materials forming curved and flexible screens; and

- a phase change material (PCM) capable of absorbing or releasing heat when undergoing a phase change, for use in energy storage. Examples of PCMs include molten aluminum phosphate, ammonium carbonate, ammonium chloride, cesium carbonate, cesium sulfate, calcium citrate, calcium chloride, calcium hydroxide, calcium oxide, calcium phosphate, calcium saccharate, calcium sulfate, cerium phosphate, iron phosphate, lithium carbonate, lithium sulfate, magnesium chloride, calcium sulfate magnesium, manganese chloride, manganese nitrate, manganese sulfate, potassium acetate, potassium carbonate, potassium chloride, potassium phosphate, rubidium carbonate, rubidium sulfate, disodium tetraborate, sodium acetate, sodium bicarbonate, sodium bisulfate, sodium citrate, sodium chloride, sodium hydroxide, sodium nitrate, sodium percarbonate, sodium persulfate, sodium phosphate, sodium propionate, sodium selenite, sodium silicate, sodium sulfate, sodium tellurate, sodium thiosulfate, strontium hydrophosphate, zinc acetate, zinc chloride, sodium thiosulfate, paraffinic hydrocarbon waxes and polyethylene glycols.

"Crosslinking agent" means a compound bearing at least two reactive functions capable of crosslinking a monomer or an oligomer, or a mixture of monomers or oligomers, during its polymerization. Advantageously, the crosslinking agent may be chosen from molecules bearing at least two functions chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions. Advantageously, the crosslinking agent may be chosen from the group consisting of:

- diacrylates, such as 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,4-butanediol dimethacrylate, 2,2-bis(4-methacryloxyphenyl) propane, 1,3-butanediol dimethacrylate, 1,10-decanediol dimethacrylate, bis(2-methacryloxyethyl) N,N'-1,9-nonylene biscarbamate, 1,4-butanediol diacrylate, ethylene glycol diacrylate, 1,5-pentanediol dimethacrylate, 1,4-phenylene diacrylate, allyl methacrylate, N,N'-methylenebisacrylamide, 2,2-bis[4-(2-hydroxy-3- [methacryloxypropoxy]phenyl]propane, tetraethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate triethylene glycol diacrylate, triethylene glycol dimethacrylate, polyethylene glycol diglycidyl ether, N,N- diallylacrylamide, 2,2-bis[4-(2-acryloxyethoxy)phenyl]propane, glycidyl methacrylate;

- multifunctional acrylates such as dipentaerythritol pentaacrylate, 1,1,1-trimethylolpropane triacrylate, 1,1,1-trimethylolpropane trimethacrylate, ethylenediamine tetramethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate; and

- acrylates also having another reactive function, such as propargyl methacrylate, 2-cyanoethyl acrylate, tricyclodecane dimethanol diacrylate, hydroxypropyl methacrylate, N-acryloxysuccinimide, N-(2-

Hydroxypropyl)methacrylamide, N-(3-aminopropyl)methacrylamide hydrochloride, N-(t-BOC-aminopropyl)methacrylamide hydrochloride, 2-aminoethyl methacrylate hydrochloride, monoacryloxyethyl phosphate, o-nitrobenzyl methacrylate, acrylic anhydride, 2-(tert-butylamino)ethyl methacrylate, N, N-diallylacrylamide, glycidyl methacrylate, 2-hydroxyethyl acrylate, 4-(2-acryloxyaethoxy)-2-hydroxybenzophenone, N-(Phthalimidomethyl)acrylamide, cinnamyl methacrylate.

“Amphiphilic molecule” refers to a molecule having at least one hydrophilic group and at least one hydrophobic group. “Amphiphilic oil phase” means an oil phase comprising at least one amphiphilic molecule, allowing the oil phase to exhibit an affinity for both hydrophobic and hydrophilic media.

“Comprising” or “comprise” or “containing” or “contain” shall be construed in an open and inclusive sense, but not limited thereto. In one embodiment, “comprising” means “consisting essentially of.” In one embodiment, “comprising” means “consisting of,” which shall be construed as limited thereto.

“From X to Y” refers to the range of values between X and Y, with the X and Y limits included in this range.

"Mean diameter" means the diameter Dn50. Dn50 is the median of the number-averaged droplet size distribution. The droplet size distribution, and thus the mean droplet diameter, can be measured by methods well known to those skilled in the art, for example by a light scattering technique (for example using a Mastersizer 3000 equipped with a hydro SV measuring cell), or by the analysis of optical microscopy images, or by the analysis of transmission electron microscopy (TEM) images. "Emulsion" means a dispersion of two immiscible liquids, i.e. a fluid colloidal system in which liquid droplets are dispersed in a liquid. It consists of a dispersed phase present in the form of droplets surrounded by a continuous phase. The size of the droplets often exceeds the usual limits for colloids. A "simple emulsion" is designated by the symbol O/W (or by the term oil-in-water) if the continuous phase is an aqueous phase and by W/O (or by the term water-in-oil) if the continuous phase is an oily phase (e.g. organic liquid).

“Approximately” before a digit or number means plus or minus 10% of the nominal value of that digit or number. In one embodiment, “approximately” before a digit or number refers to plus or minus 5% of the nominal value of that digit or number.

“Drop” or “droplet” means a small particle of liquid. Unless otherwise specified, for the purposes of this application, a “drop” is a “single drop”, that is, a drop consisting of a single phase.

“Hydrophilic” refers to the ability of a molecular entity to interact with polar solvents, particularly water.

"Initiator" means any substance introduced into the oil phase in order to cause a polymerization reaction when said initiator is excited by an energy source. The term "photoinitiator" means any substance introduced into the oil phase in order to cause a polymerization reaction when said initiator is excited by light radiation. Advantageously, the photoinitiators may be selected from the group consisting of:

- a-hydroxyketones, such as 2-hydroxy-2-methyl-l-phenyl-l-propanone;

- a-aminoketones, in particular 2-benzyl-2-dimethylamino-l-(4-morpholinophenyl)-butanone-1;

- aromatic ketones or thioxanthones, and quinones. These aromatic ketones most often require the presence of a hydrogen donor compound such as tertiary amines and especially alkanolamines; - a-dicarbonyl derivatives, the most common of which is benzyldimethylketal

- acylphosphine oxides, such as, for example, bis-acylphosphine oxides (BAPO); and

- other photoinitiators, including aromatic ketones such as benzophenone, phenylglyoxylates such as phenylglyoxylic acid methyl ester, oxime esters such as [l-(4-phenylsulfanylbenzoyl)heptylideneamino]benzoate, sulfonium salts, iodonium salts and oxime sulfonates.

"Catastrophic inversion" or "phase inversion" means a change in the respective dispersion of two phases in contact in an emulsion.

"Metastable" means, for a physicochemical system, a physicochemical system which is not stable but whose very low transformation rate makes it appear stable.

"Monomer" means a molecule that can undergo polymerization and thus contribute to the constitutional units of the essential structure of a macromolecule. "Oligomer" means a macromolecule comprising a repetition of monomers, preferably a repetition of less than 10 monomers. Advantageously, the "monomers or oligomers" may be chosen from monomers and oligomers comprising at least one reactive function chosen from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, mercaptoester, thiolene, siloxane, epoxy, oxetane, urethane, isocyanate and peroxide functions. More advantageously, the monomers or oligomers may be selected from the group consisting of aliphatic or aromatic esters or polyesters, methanes or polyurethanes, anhydrides or polyanhydrides, saccharides or polysaccharides, ethers or polyethers, amides or polyamides, and carbonates or polycarbonates, wherein the monomers or oligomers further comprise at least one reactive group selected from the group consisting of acrylate, methacrylate, vinyl ether, N-vinyl ether, vinyl ester, thiolene, maleate, epoxy, siloxane, amine, lactone, phosphate and carboxylate groups. Even more advantageously, the monomers or oligomers may be selected from among the monomers or oligomers carrying at least one of the abovementioned reactive functions and also carrying at least one function chosen from the group consisting of primary, secondary and tertiary alkylamine functions, quaternary amine functions, sulfate, sulfonate, phosphate, phosphonate, carboxylate, hydroxyl, halogen functions and mixtures of these functions.

"Aqueous phase" means a liquid phase comprising at least one solvent selected from the group consisting of water, hydrophilic organic solvents and combinations thereof. According to the invention, the aqueous phase and the oily phase are immiscible with each other, which means that the amount by weight of the aqueous phase capable of being solubilized in the oily phase is less than or equal to 5%, preferably less than 1%, more preferably less than 0.5%, or even preferably equal to 0%, relative to the total weight of the oily phase, and that the amount (by weight) of the oily phase capable of being solubilized in the aqueous phase is less than or equal to 5%, preferably less than 1%, more preferably less than 0.5%, or even preferably equal to 0%, relative to the total weight of the oily phase. 5%, more preferably 0%, relative to the total weight of the aqueous phase. Advantageously, the immiscibility between the aqueous phase and the oily phase makes it possible to avoid the migration of active agent(s) possibly present in the aqueous phase from said aqueous phase to the oily phase and/or to avoid the migration of active agent(s) possibly present in the oily phase from said oily phase to the aqueous phase.

"Oily phase" means a liquid phase immiscible with an aqueous phase, which means that the amount by weight of an aqueous phase capable of being solubilized in the oily phase is less than or equal to 5%, preferably less than 1%, more preferably less than 0.5%, or even preferably equal to 0%, relative to the total weight of the oily phase, and that the amount (by weight) of the oily phase capable of being solubilized in an aqueous phase is less than or equal to 5%, preferably less than 1%, more preferably less than 0.5%, or even preferably equal to 0%, relative to the total weight of the aqueous phase. 5%, more preferably 0%, relative to the total weight of the aqueous phase. The oily phase does not does not necessarily contain oil. The oil phase typically has a viscosity greater than the viscosity of water.

“Polymerization” or “crosslinking” means the process of converting a mixture of monomers and/or oligomers into a polymer.

“Crosslinkable” means a composition capable of polymerizing (crosslinking) to form a solid material.

“Rpm” or “revolutions per minute” refers to the number of revolutions in one minute.

"Shear rate Y" refers to the velocity gradient in a moving fluid. The "shear stress o" applied to an emulsion drop is defined as the tangential force per unit area of the drop resulting from the macroscopic shear applied to the emulsion during its stirring. The shear stress G (expressed in Pa), the viscosity r] (expressed in Pa.s) and the shear rate Y (expressed in s' ¹ ) applied to an emulsion during its stirring are related by the following equation: o = Î]Y.

"Surfactant" means a substance that lowers the surface tension of the medium in which it is dissolved and/or the interfacial tension with other phases and that, as a result, is positively adsorbed at liquid/vapor, liquid/liquid and/or other interfaces. A composition, emulsion, or phase that "does not comprise a surfactant" is a composition, emulsion, or phase that comprises less than 0.1% w/w of any surfactant, preferably less than 0.01% w/w of any surfactant, more preferably less than 0.001% w/w of any surfactant, even more preferably it does not comprise any surfactant (i.e. 0% w/w of any surfactant).

"Surface tension y" is the work required to increase a surface area divided by that area. When two phases are studied, it is called "interfacial tension y"; "interfacial tension y" is the change in Gibbs energy per unit change in interfacial area for substances in physical contact.

"Viscosity" or "dynamic viscosity" means, for a laminar flow of a fluid, the ratio between the shear stress and the velocity gradient perpendicular to the shear plane. Viscosity can be measured by methods well known to those skilled in the art. Unless otherwise indicated, viscosity, in the present application, is measured by any viscosity measurement method well known to those skilled in the art. In particular, viscosity may be measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter cone, a 2 degree angle with a plate geometry and a temperature control cell set at 25 °C, the viscosity value being read at a shear rate ranging from 0.1 s' ¹ to 1000 s' ¹ , preferably at a shear rate equal to 10 s' ¹ . "Viscosity ratio p", "Dynamic viscosity ratio p" or "p" denotes the ratio of the dynamic viscosity of the dispersed phase to that of the continuous phase:

[Math 3] r/disp p = - pcont in which rjdisp is the viscosity of the dispersed phase and r| _C ont is the viscosity of the continuous phase.

"(p), in the case of a simple emulsion, is the volume fraction of internal phase, i.e. the volume percentage of the dispersed phase incorporated in the simple emulsion, relative to the total volume of the simple emulsion.

"(pmax" is the maximum volume percentage of the dispersed phase incorporated into a simple emulsion, before the phase inversion of the emulsion is observed, relative to the total volume of the emulsion. For example, in a water-in-oil emulsion, "(pmax" is the volume percentage of the aqueous phase incorporated into the oily phase, before the phase inversion of the emulsion is observed. According to the present invention, (pmax is preferably equal to or greater than 40% by volume relative to the total volume of the simple W/O emulsion, more preferably (pmax is between 40% by volume and 95% by volume relative to the total volume of the simple W/O emulsion. A "high (pmax" is equal to or greater than 64% v/v relative to the total volume of the emulsion. An emulsion having a (pmax equal to or greater than 40% v/v, preferably equal to or greater than 64% v/v, relative to the total volume of the emulsion is an "emulsion with high internal phase”. DETAILED DESCRIPTION

Process for the preparation of a simple water-in-oil emulsion

The present invention relates to a method for manufacturing a simple water-in-oil emulsion not comprising a surfactant, comprising a step of dropwise addition of an aqueous phase to an oily phase, said oily phase being amphiphilic.

Advantageously, in said method, one or more of the following characteristics are met:

1) an adhesion energy exists between two aqueous phase droplets dispersed in the oil phase, preferably the adhesion energy between two aqueous phase droplets dispersed in the oil phase is 10' ⁵ J.nT ² to 10' ³ J.nT ² ;

2) said aqueous phase may comprise a compound chosen from at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, and optionally at least one photoinitiator;

3) said oily phase may comprise a compound chosen from at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, and optionally at least one photoinitiator;

4) the dropwise addition of the aqueous phase to the oily phase is carried out at a flow rate of 0.001 mL.s' ¹ to 50 mL.s' ¹ , preferably of 0.001 mL.s' ¹ to 20 inL.s' x, more preferably of 0.001 mL.s' ¹ to 10 mL.s' ¹ , even more preferably of 0.001 mL.s' ¹ to 0.2 mL.s' ¹ , better still of 0.001 mL.s' ¹ to 0.05 mL.s' ¹ , even better still of approximately 0.01 mL.s'¹;

5) the mixture comprising the aqueous phase and the oily phase is continuously stirred, preferably at a stirring speed of 100 rpm to 3000 rpm, more preferably at a stirring speed of 500 rpm to 2500 rpm;

6) the shear rate applied during agitation is from 1000 s' ¹ to 4000 s' ¹ , preferably from 2000 s' ¹ to 3000 s'¹;

7) the ratio between the dynamic viscosity of the aqueous phase and the viscosity of the oil phase is from 0.01 to 20, preferably from 0.01 to 10, more preferably from 0.1 to 10, even more preferably from 1 to 10, the dynamic viscosities being measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter cone, a 2 degree angle and a temperature control cell set at 25 °C;

8) the interfacial tension y between the aqueous phase and the oily phase is from 0 J.nT ² to 50xl0' ³ J.nT ² , preferably from 20xl0' ³ J.nT ² to 40xl0' ³ J.nT ² .

Preferably, the present invention relates to a method for manufacturing a simple water-in-oil emulsion not comprising a surfactant, comprising a step of dropwise addition of an aqueous phase to an oily phase, in which the oily phase is amphiphilic and in which an adhesion energy between two droplets of aqueous phase dispersed in the oily phase is from 10' ⁵ J.nT ² to 10' ³ J.nT ² .

Indeed, the inventors of the present invention have surprisingly discovered that, in surfactant-free systems, adhesion between two aqueous phase droplets dispersed in the oily phase is necessary and sufficient to ensure stability of the simple emulsion. The metastability of surfactant-free water-in-oil simple emulsions is therefore correlated with adhesion. Adhesion has been observed for different families of oily phases, which makes this phenomenon non-specific to a given system.

The inventors of the present invention have surprisingly discovered that an adhesion energy range from 10' ⁵ J.nT ² to 10' ³ J.nT ² between two aqueous phase droplets dispersed in the oily phase allows the resulting simple emulsion to be particularly stable, even in the absence of surfactant.

More advantageously, the adhesion energy between two aqueous phase droplets dispersed in the oily phase is from 10' ⁵ J.nT ² to 10' ⁴ J.nT ² .

In addition, the emulsions according to the present invention have a high aqueous phase volume fraction (p) which can reach 70% to 90%.

The present invention relates to a method for manufacturing a simple water-in-oil emulsion not comprising a surfactant, comprising a step of adding dropwise an aqueous phase to an oily phase, in which an adhesion energy exists between two droplets of aqueous phase dispersed in the oily phase and in which the oily phase is amphiphilic.

Advantageously, the dropwise addition of the aqueous phase to the oily phase is carried out so that (p remains strictly less than (pmax, where (p is the volume fraction of internal phase and (pmax is the volume fraction of internal phase at which a phase inversion of the emulsion is observed. In particular, the method for manufacturing a simple water-in-oil emulsion according to the invention may further comprise a control step, so that the dropwise addition of the aqueous phase to the oily phase is stopped before (p reaches (pmax, so that (p remains strictly less than (pmax. More particularly, the method for manufacturing a simple water-in-oil emulsion according to the invention may further comprise a control step, so that the dropwise addition of the aqueous phase to the oily phase is stopped before (p reaches (pmax, so that (p remains strictly less than (pmax, then a step of recovering the emulsion simple water-in-oil obtained.

Advantageously, an adhesion energy exists between two droplets of aqueous phase dispersed in the oily phase, preferably the adhesion energy between two droplets of aqueous phase dispersed in the oily phase is from 10' ⁵ J.nT ² to 10' ³ J.nT ² .

Advantageously, said oily phase comprises at least one oil.

Preferably, at least one oil is a polar oil, its polarity being greater than 0 Debeye (D), preferably greater than 0.1 D, and more preferably greater than 0.5 D.

Advantageously, F at least one oil is selected from the group consisting of: silicone oils, poly(acrylate) oil, polyester oil, mineral oils, vegetable oils and mixtures thereof. More advantageously, F at least one oil is selected from the group consisting of: silicone oils, poly(acrylate) oil, polyester oil, vegetable oils and mixtures thereof. Even more advantageously, F at least one oil is selected from the group consisting of: silicone oils, poly(acrylate) oil, polyester oil, and mixtures thereof. Advantageously, at least one oil may be a vegetable oil, preferably a vegetable oil chosen from the group consisting of: soybean oil, sunflower oil, jojoba oil, coconut oil, lanolin oil, castor oil, their derivatives and their mixtures.

More preferably, F at least one oil may be a silicone oil, preferably a silicone oil selected from the group consisting of: poly(dimethylsiloxane) (PDMS), poly(monomethylsiloxane) (PPMS), poly(dimethylsiloxane) hydroxy terminated (PDMS-OH) and mixtures thereof, preferably the silicone oil is poly(dimethylsiloxane) hydroxy terminated (PDMS-OH).

According to one embodiment, the at least one oil of the oily phase consists of PDMS-OH. Indeed, the at least one oil of the oily phase consisting of PDMS-OH has proven to be extremely effective with a (pmax greater than 90%, for example in an aqueous phase / oily phase system composed of glycerol (1 Pa.s) / PDMS-OH (from 1 to 10 Pa.s).

Advantageously, the oily phase comprises at least one crosslinking agent; at least one compound chosen from oligomers, monomers and their mixtures; and optionally at least one photoinitiator.

Advantageously, the aqueous phase comprises at least one of water, glycerol, an aqueous glycerol solution, an aqueous alginate solution and mixtures thereof. More advantageously, the aqueous phase comprises at least one of glycerol, an aqueous glycerol solution, an aqueous alginate solution and mixtures thereof.

Advantageously, the aqueous phase comprises at least one crosslinking agent; at least one compound chosen from oligomers, monomers and their mixtures; and optionally at least one photoinitiator.

According to a particular embodiment, the oily phase comprises a silicone oil having a viscosity ranging from 0.05 to 30 Pa.s and the aqueous phase comprises at least one of glycerol, an aqueous glycerol solution, an aqueous alginate solution and mixtures thereof. According to another particular embodiment, the oily phase comprises a polyacrylate having a viscosity ranging from 1 to 25 Pa.s and the aqueous phase comprises at least one of glycerol and an aqueous glycerol solution. According to another particular embodiment, the oily phase comprises a polyurethane having a viscosity of 10 Pa.s and the aqueous phase comprises at least one of glycerol and an aqueous glycerol solution. According to another particular embodiment, the oily phase comprises a polyester having a viscosity of 2 Pa.s and the aqueous phase comprises at least one of glycerol and an aqueous glycerol solution. Indeed, the inventors of the present application have surprisingly discovered that these four W/O systems exhibit adhesion, the adhesion energy between two aqueous phase droplets dispersed in the oily phase ranging from 10' ⁵ J.nT ² to 10' ³ J.nT ² , and allows the production of a simple emulsion having significant metastability.

Advantageously, the content of at least one compound chosen from oligomers, monomers and their mixtures, present in the aqueous phase according to the invention, ranges from 50% to 99% by weight relative to the total weight of the aqueous or oily phase.

Advantageously, the content of at least one crosslinking agent, present in the aqueous phase according to the invention, ranges from 1% to 20% by weight relative to the total weight of the aqueous or oily phase.

Advantageously, the content of the optional at least one initiator ranges from 0.1% to 5% by weight relative to the total weight of the aqueous phase. More advantageously, the content of the optional at least one photoinitiator ranges from 0.1% to 5% by weight relative to the total weight of the aqueous or oily phase.

According to one embodiment, the aqueous or oily phase may comprise at least one active agent. Advantageously, the aqueous or oily phase comprises from 1% to 99% by weight, preferably from 5% to 95% by weight, more preferably from 10% to 90% by weight, even more preferably from 20% to 80% by weight, better still from 30% to 70% by weight, even better still from 30% to 60% by weight, of at least one active agent, relative to the total weight of the aqueous or oily phase.

The aqueous phase is added dropwise to the oily phase. Advantageously, the aqueous phase is added dropwise to the oily phase at a flow rate ranging from 0.001 mL.s' ¹ to 50 mL.s' ¹ , preferably from 0.001 mL.s' ¹ to 20 mL.s' ¹ , more preferably from 0.001 mL.s' ¹ to 10 mL.s' ¹ , even more preferably from 0.001 mL.s' ¹ to 0.2 mL.s' ¹ , better still from 0.001 mL.s' ¹ to 0.05 mL.s' ¹ , even better still at a flow rate of about 0.01 mL.s' ¹ . Advantageously, the aqueous phase is added dropwise to the oily phase at a flow rate of approximately 0.001 mL.s' ¹ , 0.007 mL.s' ¹ , 0.01 mL.s' ¹ , 0.1 mL.s' ¹ , 1 mL.s' ¹ , 1.5 mL.s' ¹ , 2 mL.s' ¹ , 3 mL.s' ¹ , 4 mL.s' ¹ , 5 mL.s' ¹ , 6 mL.s' ¹ , 7 mL.s' ¹ , 8 mL.s' ¹ , 9 mL.s' ¹ , 10 mL.s' ¹ , 15 mL.s' ¹ , 20 mL.s' ¹ , 25 mL.s' ¹ , 30 mL.s' ¹ , 35 mL.s' ¹ , 40 mL.s' ¹ , 45 mL.s' ¹ or 50 mL.s' ¹ .

In the process according to the invention for preparing a simple water-in-oil emulsion, the aqueous phase is advantageously at a temperature ranging from 0°C to 100°C, preferably from 10°C to 80°C, more preferably from 15°C to 60°C. In the process according to the invention for preparing a simple water-in-oil emulsion, the oily phase is advantageously at a temperature ranging from 0°C to 100°C, preferably from 10°C to 80°C, more preferably from 15°C to 60°C.

Advantageously, the mixture comprising the aqueous phase and the oily phase is continuously stirred during the dropwise addition of the aqueous phase, preferably at a stirring speed ranging from 100 rpm to 3000 rpm, more preferably at a stirring speed ranging from 500 rpm to 2500 rpm, even more preferably at a stirring speed ranging from 500 rpm to 2000 rpm.

Advantageously, stirring makes it possible to emulsify the mixture of the oily phase and the aqueous phase.

Advantageously, when the drops of the aqueous phase come into contact with the oily phase under agitation, the drops of the aqueous phase are dispersed, still in the form of drops, called simple drops.

Advantageously, the stirring is preferably mechanical stirring. Advantageously, any type of stirrer commonly used to form emulsions may be used, such as a mechanical paddle stirrer, a static emulsifier, an ultrasonic homogenizer, a membrane homogenizer, a high-pressure homogenizer, a colloid mill, a high-shear disperser, or a high-speed homogenizer. Advantageously, the stirring of the mixture comprising the aqueous phase and the oily phase may be carried out in a stirrer. This stirrer may be selected from the group consisting of an overhead mixer equipped with blades, a vortex device, a static mixer, and a rotary mixer. Preferably, this agitator is an anchor mixer (i.e., an overhead mixer equipped with an anchor). More preferably, the blades of the overhead mixers equipped with blades are selected from the group consisting of helical blades, sawtooth blades, cross blades, straight blades, inclined blades, ringed blades, anchor, propeller, radial flow, cross blades, centrifugal blades, half-moon blades, serpentine blades, beater blades, chain blades, and any combination thereof. More preferably, the vortex device may be a large capacity tubular frame vortex mixer, preferably a large capacity tubular frame vortex mixer that is orbital, vertical, or horizontal. More preferably, the static mixer is selected from the group consisting of helical static mixers, plate-shaped static mixers, low pressure drop static mixers and interfacial surface generating mixers. More preferably, the rotary mixer is selected from the group consisting of planetary mixers, orbital mixers, including tank mixers for industrial scale production, and Couette mixers (as described in FR 9604736).

Advantageously, the shear rate applied during stirring ranges from 1000 s' ¹ to 4000 s' ¹ , preferably from 2000 s' ¹ to 3000 s' ¹ .

Advantageously, the shear rate applied during stirring ranges from 10 s' ¹ to 1000 s' ¹ , preferably from 100 s' ¹ to 1000 s' ¹ .

Advantageously, the viscosity of the oily phase at 25°C and at atmospheric pressure ranges from 50 mPa.s to 500,000 mPa.s, preferably from 500 mPa.s to 100,000 mPa.s. More preferably, the viscosity of the oily phase at 25°C and at atmospheric pressure ranges from 1,000 mPa.s to 50,000 mPa.s, even more preferably from 2,000 mPa.s to 25,000 mPa.s, and for example from 3,000 mPa.s to 15,000 mPa.s.

Advantageously, the ratio between the dynamic viscosity of the aqueous phase and the dynamic viscosity of the oily phase ranges from 0.01 to 20, preferably from 0.01 to 10, more preferably from 0.1 to 10, even more preferably from 1 to 10. Indeed, the inventors have surprisingly discovered that the formation of a simple W/O emulsion with a high incorporation of aqueous phase, also called a high internal phase emulsion (which is measured by a high pmax, preferably a pmax equal to or greater than 40% w/w relative to the total weight of the W/O emulsion) is favored by a low dynamic viscosity ratio p, in particular a ratio p ranging from 0.01 to 20, preferably from 0.1 to 10, more preferably from 1 to 10, and even more preferably from 1 to 5.

Advantageously, the relatively high viscosity of the oil phase contributes to the stability of the simple emulsion.

Advantageously, the interfacial tension y between the aqueous phase and the oily phase is between 0 J.nT ² and 50xl0' ³ J.nT ² , preferably between 20xl0' ³ J.nT ² and 40xl0' ³ J.m' ² . Advantageously, such a low interfacial tension between the aqueous phase and the oily phase advantageously ensures the stability of the simple W/O emulsion according to the invention.

The inventors further surprisingly discovered that such an emulsion remains stable even in the presence of an energy barrier to droplet nucleation.

[Math 4]

EQ, = 20 k _B T with T = 298 K. Generally, surfactant-stabilized emulsions exhibit a higher energy barrier of at least 30 kuT. It is therefore surprising that the emulsions according to the invention remain so stable despite this very low activation energy for coalescence.

Advantageously, the process according to the invention for preparing a simple water-in-oil emulsion is an adaptable process (choice of phases, droplet size, fraction of the internal phase) and can be adapted to the W/O system used and depending on the final application.

Simple water-in-oil emulsion The present invention also relates to a simple water-in-oil emulsion obtained by the process for preparing a simple water-in-oil emulsion according to the invention described above.

Indeed, a simple water-in-oil emulsion obtained by the process for preparing a simple water-in-oil emulsion according to the invention described above is particularly stable despite the absence of surfactant in its composition.

Advantageously, the contact angle between two drops of aqueous phase is between 1 and 30 degrees, preferably between 10 and 30 degrees, preferably between 20 and 30 degrees, as determined from a film of the polymer in oily phase in which the aqueous phase is dispersed.

Advantageously, the morphology of the simple water-in-oil emulsion is process dependent: it depends in particular on the shear rate, the stirring speed, the rate of addition of the internal phase, the adhesion energy, the interfacial tension y between the aqueous phase and the oily phase, the viscosity ratio p, the composition of the aqueous phase and the composition of the oily phase.

Process for obtaining microcapsules

The present invention also relates to the use of a simple water-in-oil emulsion obtained according to the process for preparing a simple water-in-oil emulsion according to the invention described above, for the manufacture of microcapsules.

The present invention also relates to a method for manufacturing solid microcapsules, comprising the following steps: a) preparing a simple water-in-oil emulsion according to the method for preparing a simple water-in-oil emulsion according to the invention described above, said oily or aqueous phase comprising at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, then b) crosslinking F at least one compound of the oily or aqueous phase chosen from oligomers, monomers and their mixtures. The present invention also relates to a method for manufacturing solid microcapsules, comprising the following steps: a) preparing a simple water-in-oil emulsion according to the method for preparing a simple water-in-oil emulsion according to the invention described above, said oily phase comprising at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, then b) crosslinking F at least one compound of the oily phase chosen from oligomers, monomers and their mixtures.

The present invention also relates to a method for manufacturing solid microcapsules, comprising the following steps: a) preparing a simple water-in-oil emulsion by adding an aqueous phase to an oily phase, said emulsion not comprising a surfactant, said oily phase being amphiphilic, comprising at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, then b) crosslinking F at least one compound of the oily phase chosen from oligomers, monomers and their mixtures.

The present invention also relates to a method for manufacturing solid microcapsules, comprising the following steps: a) preparing a simple water-in-oil emulsion not comprising a surfactant by adding an aqueous phase to an oily phase, said aqueous phase comprising at least one crosslinking agent and at least one compound chosen from oligomers, monomers and their mixtures, in which an adhesion energy exists between two droplets of aqueous phase dispersed in the oily phase and in which the oily phase is amphiphilic, then b) crosslinking F at least one compound of the aqueous phase chosen from oligomers, monomers and their mixtures.

Advantageously, all the characteristics of the process for preparing a simple water-in-oil emulsion according to the invention described above (part “Process for preparing a simple water-in-oil emulsion” of the present application) apply mutatis mutandis. mutandis to step a) of the process for obtaining microcapsules of this part “Process for obtaining microcapsules” of this application.

Advantageously, step b) of crosslinking F at least one compound of the aqueous or oily phase chosen from oligomers, monomers and their mixtures, is carried out by photopolymerization, more advantageously, it is a crosslinking by ultraviolet (UV) radiation. This photopolymerization step makes it possible in particular to solidify the aqueous or oily phase and therefore to eliminate any coalescence.

Advantageously, step b) makes it possible to obtain microcapsules. More advantageously, if the aqueous phase comprises at least one active agent, step b) makes it possible to obtain microcapsules encapsulating the at least one active agent.

Advantageously, step b) consists in exposing the simple emulsion obtained in step a) to a light source capable of initiating the photopolymerization of the aqueous phase. Preferably, the light source is a UV light source. More preferably, the UV light source can emit in a wavelength ranging from 100 nm to 450 nm, even more preferably from 100 nm to 400 nm.

Advantageously, during step b), the aqueous phase of the emulsion obtained in step a) is exposed to a light source for a duration of less than 15 minutes, preferably for a duration ranging from 10 seconds to 10 minutes, more preferably for a duration ranging from 20 seconds to 200 seconds, even more preferably for a duration ranging from 20 seconds to 180 seconds, better still for a duration ranging from 30 seconds to 50 seconds, even better still for a duration of approximately 30 seconds.

Advantageously, the composition obtained at the end of step b), comprising solid microcapsules dispersed in the aqueous phase, is ready to use and can be used without any additional step of post-treatment of the capsules being necessary.

Advantageously, the method of preparing solid microcapsules according to the invention may be a continuous or batch method of preparing solid microcapsules. More advantageously, the method of the invention is a batch method. The process according to the invention for the preparation of solid microcapsules has the advantage of not requiring a surfactant for the manufacture of the solid microcapsules.

The crosslinking of step b), once completed, then ensures the thermodynamic stabilization of the simple emulsion.

Microcapsules

The present invention also relates to the microcapsules obtained by the process for obtaining microcapsules according to the invention described above (part “Process for obtaining microcapsules” of the present application).

Advantageously, the average diameter of the solid microcapsules is between 0.1 pm and 20 pm, preferably between 10 pm and 20 pm.

Use of microcapsules

The present invention also relates to the use of the microcapsules obtained by the process for obtaining microcapsules according to the invention described above (part “Process for obtaining microcapsules” of the present application) in at least one field chosen from the group consisting of agriculture, cosmetics, home care, chemistry, agrochemistry, paint, fuels, lubricants, bitumen and drilling muds.

Advantageously, the microcapsules according to the invention are used in the field of agrochemistry. Advantageously, the microcapsules according to the invention are used in a composition for agrochemistry.

The present invention also relates to a composition for agrochemistry comprising the microcapsules according to the invention.

Advantageously, the microcapsules according to the invention are used in any field other than cosmetics. More advantageously, the microcapsules according to the invention are used in at least one field chosen from the group consisting of agriculture, home care, chemicals, agrochemicals, paints, fuels, lubricants, bitumens and drilling muds.

DESCRIPTION OF FIGURES

[Fig. 1] is a schematic representation of the method for determining adhesion between two drops involving the use of an aspiration micropipette for the adhesion test.

[Fig. 2] is a graph showing the monitoring of the fraction of glycerol released over time for five emulsions according to the invention. The lines are guides for the eyes.

EXAMPLES

The present invention will be better understood by reading the following examples which illustrate the invention in a non-limiting manner.

Example 1: preparation of simple emulsions according to the invention

Materials and methods

Five emulsions according to the invention were obtained using a paddle stirrer (IKA Eurostar 40 digital) equipped with a "4-blade propeller" geometry with a diameter Dp = 50 mm. The emulsification was carried out in a glass beaker with an internal diameter Db = 55 mm. The rotation speed was set at Q = 1000 rpm, which induced a shear rate

avec s = Db - D_p, taille de l’entrefer entre le bêcher et les pâles. La phase huileuse a été introduite initialement dans le bêcher d’émulsification et la phase aqueuse a été progressivement ajoutée à l’aide d’un pousse- seringue (Harvard Apparatus PHD 2000). Le débit du pousse-seringue a été fixé à D = 25 mL/heure, ce qui a permis d’ajouter 1 goutte toutes les 2 secondes environ, permettant l’incorporation de chaque goutte avant l’ajout de matière supplémentaire. Ainsi, à tout moment la fraction volumique (p de phase interne était connue. La température du milieu était régulée en plongeant le bêcher dans un bain maintenu à 24°C. [Math 5]

with s = Db - _Dp , size of the air gap between the beaker and the blades. The oil phase was initially introduced into the emulsification beaker and the aqueous phase was gradually added using a syringe pump (Harvard Apparatus PHD 2000). The flow rate of the syringe pump was set at D = 25 mL/hour, which allowed 1 drop to be added approximately every 2 seconds, allowing each drop to be incorporated before additional material was added. Thus, at all times the volume fraction (p) of the internal phase was known. The temperature of the medium was controlled by immersing the beaker in a bath maintained at 24°C.

The composition of the formulated simple water-in-oil emulsions varied mainly by modifying the oil phase. Three types of oils corresponding to this description were used: three silicone oils including a polydimethylsiloxane with methyl ends (PDMS, SIGMA 378399), a polyphenylmethylsiloxane (PPMS, SIGMA 10842) and a polydimethylsiloxane with hydroxy ends (PDMS-OH, SIGMA 481963), a polyester oil (Priolube 1847, CRODA), a polyacrylate oil (GENOMER 2312, RAHN).

The viscosity of each oil was measured using an AR-G2 rheometer (TA Instruments) with imposed stress in cone-plate geometry (D = 3 cm, 9 = 2°). All the oils tested showed Newtonian behavior over a shear range of up to 1000 s' ¹ . In the case of the polyacrylate oil, its viscosity being greater than 20 Pa.s, the choice was made to use it diluted to 83% in F anisole (SIGMA 123226, Reagent Plus 99%) to bring it down to a viscosity close to 1 Pa.s.

Also to promote efficient fragmentation, the viscosity ratio

[Math 3] r/disp p = - pcont was chosen close to 1 using glycerol (SIGMA G7757, ReagentPlus 99%) in the internal phase. Glycerol has the advantage of being a viscous and Newtonian liquid over the same shear range as the formulated oils. For comparison, a fluorinated oil (PFPE, Fomblin YR) was also used in the internal phase. The voltage interfacial tension is measured using a Kruss DSA30 tensiometer using the hanging drop method. All the properties of the different materials at 25 °C (viscosity, interfacial tension and density), are summarized in the following table (the interfacial tensions are given relative to glycerol except for PFPE for which the interfacial tension is given relative to PDMS):

[Table 1]

Results

Microscopic observation of the five emulsions according to the invention (glycerol/PDMS, glycerol/PPMS, glycerol/PDMS-OH, glycerol/polyester, glycerol/polyacrylate (diluted)) shows drops with a diameter of the order of 1 to 10 pm.

Quite surprisingly, the emulsions formulated according to the invention have the particularity of acquiring a metastability such that they can be concentrated to volume fractions well above the compact stacking threshold. Thus, the emulsions according to the invention have a high aqueous volume fraction, greater than 60% v/v and preferably approximately 80% v/v, thanks to their metastability characterized by an absence of immediate destabilization such as flocculation/coagulation, sedimentation, creaming or coalescence. Emulsions are then obtained which have the characteristics of viscoelastic fluids, and the viscoelastic character makes it possible to control the properties of the droplets (for example their size, geometry and the dispersion of their sizes), by example by controlling the shear rate. In addition, the viscoelastic character can provide an interesting texture for cosmetic applications of the emulsion, and improve the pumpability/handling of the emulsion for material applications.

Example 2: Comparison of the stability of two emulsions prepared in Example 1: PFPE/PDMS for comparison and Glycerol/PDMS according to the invention

Materials and methods

The two emulsions PFPE/PDMS and glycerol/PDMS prepared according to example 1 are studied, the two emulsions differ only by the dispersed phase and by fixing (p=60%.

The emulsions are centrifuged in order to assess their stability: they are introduced into a polyamide centrifuge tube. Each sample occupies a volume of 2 mm thickness, 10 mm width and 20 mm height. The emulsions are then centrifuged using a LUMiEuge™ device (LUM GmbH) capable of applying a maximum acceleration of 2300 g. This centrifuge is equipped with an optical system that measures the transmission coefficient through the sample over time. From the transmission data, established over the entire length of the sample, the profile is drawn up. On this profile, 3 boundaries can be distinguished: the meniscus corresponding to the air/liquid interface of the emulsion (1), the sedimentation/creaming front (2) and finally the separation front between the two phases (3) (Fig. 2.3). The dispersed phase, PEPE or glycerol, is denser than the continuous phase: it then occupies the lower fraction of the centrifuged sample.

When centrifuging emulsions, since we are focusing on their stability, we are only interested here in the separation front between the two phases.

As coalescence occurs in the emulsion, macroscopic domains appear that correspond to the progressive phase separation. Under the effect of centrifugal acceleration, the dispersed phase being denser than the continuous phase, the separation front is located at the lower end of the sample. Analytical centrifugation allows a simple measurement of the height H of this front, which therefore corresponds to the quantity of dispersed phase extracted from the emulsion, in order to follow the destabilization kinetics.

Results

The PFPE/PDMS emulsion is a particularly unstable emulsion. After one minute of centrifugation at 2300 g, the separation is complete. This observation is confirmed by optical microscopy. Immediate coalescence can be observed at each contact between two drops.

On the other hand, the emulsion formulated with glycerol and PDMS shows astonishing stability over the same period. The separation is detected only after 4 hours of centrifugation.

These two emulsions, although formulated under the same conditions, express two radically different behaviors. On the one hand, the dispersion of fluorinated oil in PDMS shows no metastability and coalesces immediately when shearing stops. Conversely, the dispersion of glycerol in PDMS is preserved over long periods, from a few hours when subjected to an additional acceleration field, to a few days, when left to rest without stress. This difference in stability is visualized by a gap of nearly 104 s from the start of phase separation between the two emulsions, at identical continuous phase viscosities.

Example 3: Comparison of the stability of the five emulsions according to the invention prepared in Example 1

Materials and methods

In order to estimate the relative stability of the emulsions according to the invention formulated in Example 1 using the different oils, a monitoring of the phase separation without additional imposed constraint was used.

Results The results are presented in Figure 2, which represents the evolution of the emulsions made from the 5 oils as well as the measurement of the quantity of glycerol separated from the emulsions as they destabilize.

Monitoring the different emulsions then allows the oils to be classified in the following ascending order of emulsion stability: Polyacrylate < PPMS < PDMS < PDMS-OH. The Glycerol/PDMS-OH emulsion is the one with the most stability among the five emulsions.

Silicone oils are particularly effective, as the emulsions obtained remain stable for at least 2 days.

Example 4: measurement of the adhesion energy of the Glycerol/PDMS emulsion according to the invention prepared in example 1

Materials and methods

The Glycerol/PDMS emulsion according to the invention prepared in example 1 is studied: the adhesion energy present between the glycerol drops is determined by measuring the amplitude by observing the film which separates a doublet of adhesive glycerol drops dispersed in the PDMS.

For this, a glass capillary (World Precision Instrument IB 100-6, outer diameter 1 mm, inner diameter 0.58 mm) was pulled using a micropipette puller (P97, Sutter Instrument Company) and cut into a 10 μm tip using a microforge (MF830, Narishige). The capillary was filled with the oil phase and connected to a pressure control system with a negative pressure range of 0- ~25 mbar (Fluigent). A duo of adhesive droplets was then captured using the micropipette. Imaging of the oil film separating the two glycerol droplets was performed in the transverse direction using a confocal microscope (Leica SP5) using the 488 nm laser and the RT 30/70 filter. The measurement of the dark central fringe was performed with the image analysis software ImageJ. The film was therefore illuminated in the transverse direction, allowing an interference pattern to be obtained. The measurement of the radial intensity profile gives an estimate of the radius of the central spot Rp = 350nm.

From this measurement, which corresponds to the size of the black film, we first deduce the contact angle 9 between the drops:

avec RI et R2 le rayon des deux gouttes ; puis l’énergie d’adhésion correspondante, dérivée de la relation de Young-Dupré : [Math 6]

with RI and R2 the radius of the two drops; then the corresponding adhesion energy, derived from the Young-Dupré relation:

[Math 1]

E = 2y(l — cos 0)) with y, the interfacial tension between the dispersed and continuous phases.

Results

Between two drops of glycerol dispersed in PDMS, the contact angle reaches a value of 2°, i.e. an adhesion energy of 3.10' ⁵ Jhir. This adhesion energy makes it possible to obtain good metastability of the emulsion according to the invention.

Example 5: Observing membership on additional systems

Following the results of Example 4, the adsorption of PDMS at the interface is maintained even when varying the composition of both the oil and the aqueous phase. While replacing the glycerol in the aqueous phase with pure water, the adhesion is still observed.

Similarly, when PDMS is diluted in a solvent such as hexadecane, up to a proportion of 25% PDMS, emulsification is still possible and adhesion is very present.

These results indicate that without an aqueous phase, as shown by the behavior of a fluorinated oil emulsion in PDMS, adsorption and adhesion disappear. The formulated emulsion is ultimately unstable.

This behavior is not specific and extends to different oils. The adhesion, observed for a glycerol/PDMS system, is found, even very weak, in all the stable formulated systems of example 1 (glycerol/PDMS-OH, glycerol/polyester, glycerol/polyacrylate).

Without wishing to be bound by theory, it therefore seems that the stability of emulsions seems to be linked to the adsorption capacity of the molecules of the hydrophobic phase at the interface with the aqueous phase. An oily phase will adsorb all the better as its amphiphilic character is marked and the resulting emulsion is more stable. Experimentally, this adsorption leads to the existence of weak adhesion, making it possible to correlate the stability of the emulsion and adhesion.

Example 6: Tracking coalescence

The aim of this study is to probe the first moments of emulsion destabilization, when a macroscopic domain of dispersed phase cannot yet be detected. At these short times, the evolution of the emulsion size distribution carries crucial information. Microscopic observation of emulsions over several hours shows that formulated emulsions degrade mainly via coalescence events. In this case, an appreciation of the coalescence dynamics at short times is accessible by monitoring the size distribution of an emulsion over time.

The emulsion studied is polydisperse and the signal of the largest drops present randomly is largely amplified by this type of distributions averaged in R ³ . Conversely, a continuous evolution appears at the level of the smallest drops. From the number distribution, a characteristic size of the drops D[l, 0] is extracted:

[Math 7]

Schematically, coalescence can be represented by considering the increase in the volume of a drop followed throughout the process. In the case of the emulsion studied, coalescence is perfectly highlighted by the increase in the average diameter over time.

This development can be described empirically with a growth rate

avec Do le diamètre initial moyen de l’émulsion. La même expérience a été répétée en variant la température de stockage de l’émulsion. Pour chaque température, les variations des distributions de tailles et du D[l, 0] sont similaires et ces dernières montrent toutes un comportement linéaire aux temps courts. En traçant co en fonction de l/knT, la dépendance exponentielle indique que la coalescence peut être décrite par une loi d’Arrhénius telle que [Math 8]

with Do the mean initial diameter of the emulsion. The same experiment was repeated by varying the storage temperature of the emulsion. For each temperature, the variations of the size distributions and of the D[l, 0] are similar and the latter all show a linear behavior at short times. By plotting co as a function of l/knT, the exponential dependence indicates that the coalescence can be described by an Arrhenius law such that

[Math 9]

kO et Ea représentent respectivement la fréquence propre et l’énergie d’activation du mécanisme de coalescence. À 25°C, la fréquence de coalescence dans l’émulsion est estimée à k = 2. 10⁸ m^.s'¹. Ea a) = a)0e~kËT coO is deduced from the ordinate at the origin of the line while Ea = 20k/;T _r , T _r being 25°C is given by the slope. From the rate coO, we can determine a coalescence frequency per unit area kO = coO / s, s being the characteristic contact surface between the drops. By estimating this surface at 10% of the surface of a drop, we obtain kO ~ 4.10 ¹⁷ rn^.s' ¹ . Thus, the coalescence frequency per unit area k can finally be written [Math 10]

kO and Ea represent the natural frequency and activation energy of the coalescence mechanism, respectively. At 25°C, the coalescence frequency in the emulsion is estimated to be k = 2. 10 ⁸ m^.s' ¹ .

The characterization of the emulsion by a simple mean diameter is only possible if we assume that the size of the drops is homogeneous throughout the emulsion. In concentrated mode, there is no reorganization of the drops according to their size under the effect of gravity since the viscosity of the emulsion does not allow it. The distributions and mean diameters measured are therefore a fair representation of the overall behavior of the emulsion. When studying coalescence phenomena, there are two characteristic times linked on the one hand to the drainage time of the film separating two drops and on the other hand, its lifetime which depends on its probability of rupture. By placing ourselves at high volume fractions, the continuous phase films are already drained, which makes it possible to directly probe their probability of rupture. The measurement of k is therefore a direct measurement of the stability of water/oil/water thin films, and considering the emulsion on a macroscopic scale makes it possible to average the measurement over a large number of films. On the one hand, kO, the natural frequency, gives the number of events initiated per unit area and time. The success of each event is given by a probability that depends on the activation energy

[Math 11]

Ea e~kBT

At 25°C, this is therefore approximately 1 event in 10 ⁹ that succeeds. Typically, for conventional emulsions with similar properties, the activation energies recorded are greater than 30 kuD. Only 1 event in 10 ¹³ or more is successful. In fact, by comparing only the activation energies, a glycerol/PDMS emulsion should not be stable since its energy is much lower. The major difference comes from the natural frequency of coalescence. Indeed, values of the order of 10 ²¹ are generally recorded. The proposed coalescence mechanism is a nucleation mechanism where the rupture of the film is due to the opening and then the growth of pores within the film. This mechanism is commonly used to characterize coalescence within emulsions. The value of kO is determined by a balance between interfacial tension, which tends to favor growth, and viscosity of the film, which tends to slow it down, normalized by the volume of the pore. Thus we obtain

expression qui capture simplement toutes les dépendances de kO avec les paramètres du système. La valeur de r° est déterminée par une étude énergétique de l’étape de nucléation. La présence d’un pore de rayon r au sein d’un film liquide s’accompagne d’un côté d’une diminution de la surface de contact totale et donc d’une diminution de l’énergie surfacique associée d’un facteur -27ir²y, mais de l’autre, d’une création de surface liée aux bords de ce pore, et donc d’un coût énergétique associé d’un facteur 27trE avec E, la tension de ligne. Ainsi, l’énergie libre de création d’un pore résultante s’écrit [Math 12]

expression that simply captures all the dependencies of kO with the system parameters. The value of r° is determined by an energetic study of the nucleation step. The presence of a pore of radius r within a liquid film is accompanied on the one hand by a decrease in the total contact surface and therefore by a decrease in the associated surface energy by a factor of -27ir ² y, but on the other hand, by a creation of surface linked to the edges of this pore, and therefore by an associated energy cost of a factor of 27trE with E, the line tension. Thus, the resulting free energy of creation of a pore is written

[Math 13]

In view of this relationship, we can identify a critical radius r° such that if r < r°, the growth of the pore is not energetically favorable and any fluctuation will tend to close it and if r > r°, the growth of the pore will continue. r° is obtained by minimizing this free energy, which corresponds for nucleation to Ea, from which

soit 2r° ~ 2 nm. Ce modèle suppose en outre que l’épaisseur h du film est de l’ordre de r°. Suivant ce postulat, le film qui sépare les gouttes est très fin, typiquement épais de quelques monocouches de PDMS. [Math 14]

or 2r° ~ 2 nm. This model further assumes that the thickness h of the film is of the order of r°. Following this postulate, the film separating the drops is very thin, typically a few PDMS monolayers thick.

In the expression of kO, y and r° now being known, we deduce an effective viscosity of 10 ⁷ Pa.s, much higher than the viscosity of PDMS equal to 1 Pa.s. This viscosity does not concern the entire continuous phase but corresponds only to the viscosity of the film where coalescence occurs.

It is at this film level that the contact between two drops is made and therefore that coalescence events occur. Although performed on macroscopic samples of emulsions, the measurement of the coalescence frequency k, obtained by following the evolution of the size distribution, provides a valuable characterization of continuous phase films. The frequency k of each event was measured experimentally and obeys an Arrhenius law. The highlighted Arrhenius law is characterized by kO = 4.10 ¹⁷ rn^.s' ¹ and Ea = 20 ksTr, T _r being 25°C and implies a viscosity in the films 7 orders of magnitude higher than the viscosity of PDMS. A direct conclusion of this result is the validation of a coalescence mechanism dictated by the thermally activated nucleation of pores within the continuous phase films, similar to the behavior of classical emulsions stabilized with surfactants. The inventors of the present invention have therefore discovered that there necessarily exists, for these systems, a mechanism for stabilizing the emulsions due to the adsorption of polymers on the surface of the drops which implies on the one hand the existence of a nucleation energy barrier Ea and also a slowing down of the coalescence dynamics in the emulsion, hence the observed metastability.

Claims

1. A method of manufacturing a simple water-in-oil emulsion comprising a step of dropwise addition of an aqueous phase to an oily phase, said emulsion not comprising a surfactant, said oily phase being amphiphilic, and in which an adhesion energy is present between two droplets of aqueous phase dispersed in the oily phase. 2. The method of claim 1, wherein the adhesion energy between two dispersed aqueous phase droplets is from 10' ⁵ J.nT ² to 10' ³ J.nT ² . 3. The method of claim 1 or 2, wherein the oily phase comprises at least one oil selected from the group consisting of: silicone oils, poly(acrylate) oil, polyester oil, mineral oils, vegetable oils and mixtures thereof, preferably at least one oil is selected from the group consisting of: silicone oils, poly(acrylate) oil, polyester oil, and mixtures thereof. 4. A method according to any one of claims 1 to 3, wherein the oily phase comprises at least one silicone oil, preferably a silicone oil selected from the group consisting of: poly(dimethylsiloxane) (PDMS), poly(monomethylsiloxane) (PPMS), hydroxy terminated poly(dimethylsiloxane) (PDMS-OH) and mixtures thereof, preferably the silicone oil is hydroxy terminated poly(dimethylsiloxane) (PDMS-OH). 5. A method according to any one of claims 1 to 4, wherein the aqueous phase comprises at least one of: glycerol, poly(ethylene glycol), and alginate and mixtures thereof, preferably the aqueous phase comprises glycerol. 6. Method according to any one of claims 1 to 5, in which the dropwise addition of the aqueous phase to the oily phase is carried out at a flow rate of 0.001 mL.s' ¹ to 50 mL.s' ¹ , preferably of 0.001 mL.s' ¹ to 20 mL.s' ¹ , more preferably from 0.001 mL.s' ¹ to 10 mL.s' ¹ , even more preferably from 0.001 mL.s' ¹ to 0.2 mL.s' ¹ , better still from 0.001 mL.s' ¹ to 0.05 mL.s' ¹ , even better still from approximately 0.01 mL.s' ¹ . 7. Method according to any one of claims 1 to 6, in which the mixture comprising the aqueous phase and the oily phase is continuously stirred, preferably at a stirring speed ranging from 100 rpm to 3000 rpm, more preferably at a stirring speed ranging from 500 rpm to 2500 rpm. 8. Method according to any one of claims 1 to 7, in which the shear rate applied during stirring is from 1000 s' ¹ to 4000 s' ¹ , preferably from 2000 s' ¹ to 3000 s' ¹ . 9. A method according to any one of claims 1 to 8, wherein the ratio between the dynamic viscosity of the aqueous phase and the dynamic viscosity of the oily phase is from 0.01 to 20, preferably from 0.01 to 10, more preferably from 0.1 to 10, even more preferably from 1 to 10, the dynamic viscosities being measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter cone, a 2 degree angle and a temperature control cell set at 25°C. 10. Process according to any one of claims 1 to 9, in which the interfacial tension y between the aqueous phase and the oily phase is from 0 J.nT ² to 50xl0' ³ J.nT ² , preferably from 20xl0' ³ J.nT ² to 40xl0' ³ J.nT ² .