FR2832076A1 - EMULSIFIING COMPOSITIONS COMPRISING MODIFIED SURFACE NANOMETRIC MINERAL PARTICLES AND SURFACTANT AGENTS FORMED BY SUCH PARTICLES - Google Patents

Abstract

The invention concerns a surfactant formed by at least a particle of nanometric dimensions based on a metal phosphate or vanadate, at the surface of which are bound hydrophobic organic chains, the bonds between said chains and the surface of said particle being non-homogeneously distributed on said surface, such that the thus modified surface particle has an effective amphiphilic character. The invention also concerns emulsifying compositions comprising particles of nanometric dimensions with modified surface which can be surfactants of the type mentioned above, and the method for preparing such emulsifying compositions.

Description

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 The present invention relates to emulsifying compositions comprising surfactants formed from surface-modified solid particles, to said surfactants, as well as to methods of preparing such compositions.

 The surfactants currently known are generally molecules or macromolecules of amphiphilic nature, that is to say having on the one hand a hydrophilic region and on the other hand a hydrophobic region. This particular structure induces an orientation of these molecules when they are present at interfaces of the liquid / liquid, liquid / gas or liquid / solid type.

 In other words, surfactants can adsorb at these interfaces. This adsorption causes a lowering of the interfacial tension y and thus makes it possible to decrease the free energy of the systems which contain a large interfacial area, which induces their stabilization (foams, emulsions ...). The term surfactant comes from this decrease in interfacial tension that generates the orientation phenomenon of molecules.

 Typically, a surfactant is a molecule consisting of one or more ionic or nonionic hydrophilic group (s) and one or more hydrophobic chain (s), most often hydrocarbon (s) ). It is the exact nature of these two groups which determines the surfactant properties of the molecule obtained.

 It should therefore be emphasized that the structure of a molecular surfactant is generally relatively fixed. Therefore, it is difficult, in the general case, to confer on a surfactant other properties than properties related to its amphiphilic nature.

 Furthermore, we often observe during certain stages of concentrations (drying, etc.) of formulations using molecular surfactants, an undesirable parasitic segregation of these agents, linked to their molecular nature.

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 In order to overcome these difficulties, attempts have been made in recent years to develop solid particles having both a macroscopic and an amphiphilic character. These particles, sometimes designated by the term "Janus", have, like a molecular surfactant, a hydrophobic face and a hydrophilic face. For more details on these particular solids, reference may in particular be made to the article by De Gennes et al. "Nanoparticles and Dendrimers: hopes and illusions", in Croat. Chem. Acta, 1998, volume 71 (4), pages 833-836.

 In fact, one of the advantages of these solid particles is that, by their macroscopic nature, they have reduced mobility compared to the usual molecular surfactants.

 However, if these amphiphilic particles do indeed behave in a particular way at interfaces of the water / oil type, it cannot however be considered that they can replace the conventional molecular surfactants. In this regard, it should in particular be emphasized that these particles cannot, for example, be used as emulsifying agents, in particular because of their large size and their weakly marked amphiphilic nature.

 However, the inventors have discovered that it is possible to modify the surface of a solid particle of nanometric dimensions by organic chains of hydrophobic character so as to obtain a solid object of small dimension and having an amphiphilic character sufficiently pronounced to ensure a role of emulsifying agent.

 In a particularly surprising manner, the inventors have demonstrated that such a surface modification can be carried out on particles of specific chemical nature, which makes it possible to confer on the solid object obtained properties other than emulsifying properties.

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 On the basis of these discoveries, a first object of the present invention is to provide compositions comprising surfactants having, in addition to a marked emulsifying character, interesting physical and / or chemical properties, not linked to this amphiphilic character.

 The invention also aims to provide compositions comprising surfactants having a sufficient size giving them reduced mobility, and nonetheless capable of replacing conventional molecular surfactants, at least in certain applications, and in particular in processes of emulsification.

 Another object of the invention is to provide emulsifying compositions based on surfactants with a solid character which can advantageously replace the emulsifying compositions generally used, for example for producing emulsions, reverse emulsions or d multiple emulsions, ensuring sufficient stabilization of the emulsion while also benefiting from the solid nature and the physicochemical properties of the surfactants used.

 Thus, according to a first aspect, the subject of the present invention is an emulsifying composition comprising particles of nanometric dimensions based on a metallic compound chosen from a phosphate or a vanadate, to the surface of which organic chains of hydrophobic nature are linked, said composition having specifically an emulsifying nature such that it makes it possible to produce an emulsion of the water in oil or oil in stabilized water type, characterized by a content in dispersed phase greater than or equal to 20%, preferably greater than or equal at 30%, and preferably greater than or equal to 40%, and where the average size of the drops forming the dispersed phase is less than or equal to 20 microns, preferably less than or equal to 10 microns, advantageously less than or equal to 5 microns, and even more advantageously less than or equal to 3 microns, or even less than or equal to 1 micron.

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 By the term "stabilized" emulsion is meant, within the meaning of the present invention, an emulsion of the water in oil type (reverse emulsion) or oil in water (direct emulsion) where the phenomena of coalescence between the drops of the dispersed phase are reduced enough so that the rupture of the emulsion is not observed following storage of said emulsion for a period greater than or equal to 3 days, advantageously for a period at least equal to 7 days, and preferably for a period at least equal to 30 days. In a particularly advantageous manner, a stabilized emulsion within the meaning of the invention is such that its structure remains stable after being subjected to centrifugation carried out at a speed greater than or equal to 4000 revolutions per minute and for a duration of at least twenty minutes.

 In most cases, the emulsifying compositions of the present invention have an emulsifying character sufficient to make it possible to produce stabilized emulsions of water in oil type (reverse emulsions) characterized by contents in aqueous phase greater than or equal to 40%, and in which the average size of the drops of the dispersed phase is at most 20 microns, most often at most 10 microns, and advantageously at most 5 microns.

 Preferably, the particles of nanometric dimensions based on phosphate or metallic vanadate present in the emulsifying compositions of the present invention, to the surface of which organic chains of hydrophobic nature are linked, are such that, on the surface of most of these particles, the links between said chains and the surface are distributed in a non-homogeneous manner, so that each of the surface particles thus modified has an effective amphiphilic character, that is to say that, when it is placed in a two-phase water / oil medium such as a two-phase medium of water / ethyl acetate, water / hexane, or water / octanol type, said particle is localized specifically at the interface between the two phases present. This amphiphilic character can in particular be put

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 in evidence using a test of the type described by Nakahama et al. in Languir, volume16, pp. 7882-7886 (2000).

 The surfactants formed by such particles of nanometric dimensions of surface modified by organic chains of hydrophobic character, distributed in a non-homogeneous manner on the surface, whereby the modified surface particle has an effective amphiphilic character, are new and constitute, according to a particular aspect, another object of the present invention.

 Without wishing to be linked to any particular theory, it seems that the effective amphiphilic nature of the surfactants present in the compositions of the present invention is explained by the fact that these agents have a structure specifically comprising a zone (1) of generally hydrophilic character. , at least partially due to the hydrophilic character of the surface of the particle, and a zone (2) of generally hydrophobic character, due to the presence of chains of hydrophobic character.

 By the term "particle of nanometric dimensions" is meant, within the meaning of the present invention, an isotropic or anisotropic particle whose dimension (s) characteristic (s) average (s) is or are included (s) between 2 and 300 nm.

 The particles of nanometric dimensions present in the compositions of the invention can be of isotropic or spherical morphology.

In this case, the average diameter of the particles is advantageously between 2 and 150 nm, this average diameter being advantageously less than or equal to 100 nm, preferably less than or equal to 50 nm, and particularly advantageously less than or equal to 10 nm . Thus, the average diameter of a particle of isotropic or spherical morphology present in a composition of the invention is advantageously between 2 and 6 nm.

 According to another particular variant, the particles of nanometric dimensions present in the compositions of the invention can be

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 of anisotropic morphology, and they are then generally in the form of oblong or needle-like particles of average length generally between 5 and 250 nm, and advantageously less than or equal to 100 nm, with an anisotropy ratio generally between 2 and 300 By "anisotropy ratio" of a population of particles of anisotropic morphology, of oblong or acicular type, is meant the ratio of the average length of the particles relative to their average transverse diameter.

 Whatever their exact morphology, it is preferred that the particles present in the compositions of the invention are particles capable of having a colloidal character when they are dispersed in an aqueous and / or hydrophobic medium. Thus, a dispersion of the particles present in the compositions of the invention in an aqueous medium or in a hydrophobic medium, optionally employing mechanical desagglomeration, for example using a disperser of the Ultraturax type, advantageously leads to obtaining a dispersion of the particles having an interparticle agglomeration rate (defined by the number of particles in the agglomerated state over the total number of particles) of less than 5%, and advantageously less than 2%, the particles present being the most often essentially all individualized, and the dispersion obtained being preferably stable with respect to decantation, and advantageously having a very low tendency to interparticle re-agglomeration. The particle size distribution of the particles within a dispersion thus obtained is generally monodispersed.

 Furthermore, the particles of nanometric dimensions present in the compositions of the invention are, typically, particles based on a metal phosphate or a metal vanadate.

 Thus, according to a first variant, the particles of nanometric dimensions present in the emulsifying compositions of the invention can be particles based on a metal phosphate, that is to say, within the meaning of the invention, particles comprising, possibly in association

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with other constituents, an amorphous or crystalline metallic phosphate or an amorphous or crystalline metallic hydrogenphosphate), or a metallic phosphate (and / or hydrogenophosphate) phase in which the phosphate anions (and / or hydrogenophosphates) may be partially substituted by other types of anions, the phosphate and hydrogen phosphate anions, however, preferably remaining in the majority within this type of phase. Preferably, in this case, these particles present in the emulsifying compositions of the invention are based on an alkaline earth metal phosphate or based on a phosphate of one or more rare earth (s) , the term “rare earth” designating, within the meaning of the present description, a metal chosen from yttrium and the lanthanides, the lanthanides being the metallic elements whose atomic number is included, inclusively, between 57 (lanthanum) and 71 (lutetium). Advantageously, according to this first variant of the invention, the particles of nanometric dimensions present are based on calcium phosphate, or based on a lanthanum, cerium and / or terbium phosphate. When these particles are based on calcium phosphate, it is generally preferred that these particles comprise a calcium phosphate having: - an apatic structure of formula Ca1o-x (HP04) x (P04) 6-x (J) 2-x, where x is 0.1, or 2; and J represents an OH-, F-, C132- ion; - An apatic structure as defined above, in which a part (advantageously a minority) of the PO 4 'phosphate ions and / or a part (advantageously a minority) of the hydrogen phosphate ions HPC is substituted by carbonate ions; or - a structure of formula CaHP04, optionally hydrated, of type CaHP04, 2H20
According to another variant, the particles of nanometric dimensions present in the emulsifying compositions of the invention

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 may be particles based on a metallic vanadate, that is to say, within the meaning of the invention, particles comprising, optionally in combination with other constituents, an amorphous or crystalline, and preferably crystalline, metallic vanadate. In this case, it is advantageously particles based on a vanadate of one or more rare earths, the term rare earth having the abovementioned meaning. In this case, it is preferably particles based on yttrium vanadate, or based on yttrium vanadate in which part of the yttrium cations are substituted by cations of europium or of thulium Tm.

 Whatever their exact constituents, the particles present in the compositions of the invention generally have, intrinsically, a surface of hydrophilic nature. This hydrophilic character is generally ensured by the presence, on the surface of these particles, of hydrophilic chemical species. These groups can be neutral (-OH, COOH, P04H, for example) or preferably charged, in particular of the metal cation type, of the (Met) -O (H) ... H + or (Met) -OH ... type. OH- (where Met denotes a metal), which then gives the particle a non-zero surface charge. The particles can also present surfactants, charged or not, such as citrate ions, acetate ions or amino acids generally bonded to the surface of the particle via a metal surface cation, most often by complexing bond.

 In the case of charged particles, the absolute value of the surface charge, expressed relative to the total surface of the particle, is, in the presence of the organic chain (s) linked (s), advantageously greater than 2 micro-coulombs per cm2, and preferably more than 5 microcoulombs per cm2.

 The term “organic chain of hydrophobic nature” designates, in general, an organic chain having a hydrophilic / lipophilic balance such that said chain is soluble in a hydrophobic solvent and less soluble, advantageously insoluble, in water.

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 Preferably, the “organic chains of hydrophobic nature” of the invention are chains within which the chemical groups of hydrophobic nature, of the alkylated chain type for example, represent at least 30% by mass in said chain. Thus, the organic chains of hydrophobic nature of the invention can in particular be alkyl chains, or alternatively alkyl chains modified by the presence of hydrophilic groups, of ethoxyl type for example, these groups of hydrophilic nature not representing more than 90 % by mass and advantageously representing less than 70%.

 Thus, the organic chains of hydrophobic nature linked to the surface of the particles present in the compositions of the invention are preferably alkyl chains comprising from 6 to 30 carbon atoms, and preferably from 8 to 18 carbon atoms, or polyoxyethylene-monoalkyl ethers chains in which the alkyl chain comprises from 8 to 30 carbon atoms, preferably from 8 to 18 carbon atoms, and in which the polyoxyethylene part comprises from 1 to 10 ethoxyte-CHsChO- groups.

 The number of carbon atoms, as well as the number of ethoxylated groups which may be present, must be adapted as a function of the hydrophobic and hydrophilic properties desired, respectively, for the solid surfactants present in the compositions of the invention.

 In this regard, it should be noted that the hydrophilic nature is ensured both by the hydrophilic nature of the surface of the particle and by the hydrophilic parts, of ethoxyl group type, possibly present in the organic chains linked to the particle. The hydrophobic nature is ensured by the hydrophobic parts, of the alkyl chain type, of the organic chains.

 Whatever the nature of the organic chains of hydrophobic nature used, one of their main characteristics is that they are linked to the surface of the particles of nanometric dimensions.

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 The exact nature of the bonds between the organic chains and the surface of the particles can vary to a fairly large extent. However, it can be considered that, in the general case, these bonds are of a complexing, electrostatic or hydrogen bonding type.

 Thus, the connection between the organic chains and the surface of the particles is generally ensured by the presence, at one of the ends of each of said chains, of a chemical group, most often of ionic nature, inducing a complexing, electrostatic bond. or of the hydrogen bond type with at least one species present on the surface of the particles (metal cations, ionic chemical group or not, surfactant). In this case, the particles present are generally partially complexed by molecular surfactants of ionic type.

 It seems that the generally hydrophobic character of the zone (2) defined above for the solid surfactants present in the compositions of the invention is then ensured by the presence of the hydrophobic chains of the molecular surfactants used, the at least predominantly hydrophilic character of zone (1) being due for its part to the hydrophilic surface of the particle and to the possible residual surface charge not participating in the immobilization of molecular surfactants of ionic type bound to the surface.

 In particular so that the amphiphilic nature of the solid surfactants present is sufficiently pronounced, it is preferred that less than 90%, advantageously less than 70%, and preferably less than 50% of the surface of the particles, be engaged in the binding of the predominantly hydrophobic chains.

 As a result, the coverage rate of the surface of the particles, expressed, for each particle, by the ratio of the number of groups of molecular surfactants linked to the surface of said particle on the total surface of said particle, is preferably less than 4 groupings linked by nm2. We

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 moreover prefers that at least 2%, advantageously more than 10%, and preferably more than 20% of the surface of the particles, is involved in the complexation of the chains of predominantly hydrophobic character. Advantageously, the coverage rate of the particles present is therefore generally between 0.2 and 3.2 groups linked by nm2, preferably between 0.5 and 3 groups linked by nm2, and even more advantageously of the order of 2 groups. linked by nm2, namely preferably between 1.5 and 2.5 groups linked by nm2.

 Furthermore, in particular so as to ensure an optimal bond between the molecular surfactants and the particles, it is generally preferred to use charged particles and molecular surfactants having an ionic grouping of opposite charge.

Advantageously, the charged particles are, where appropriate, particles of positive charge. The ionic group inducing the bond is then an anionic group. Preferably, this anionic group is chosen from carboxylate, phosphate, phosphonate, phosphate ester, sulfate, sulfonate or sulfosuccinate groups. Advantageously, the organic chain (s) of hydrophobic nature used in this case are ethoxylated or non-ethoxylated alkyl chains comprising from 8 to 30 carbon atoms and from 0 to 10 ethoxylated groups. It is also possible to use amphoteric surfactant molecules such as the amine propionates, the alkyldimethylbetaines, the imidazoline derivatives, the alkylamidobetaines, or even the alkyglycines.

 The use of negatively charged particles complexed by molecular surfactants of cationic or amphoteric type is not however excluded from the subject of the invention. Furthermore, it should be emphasized that, depending on the exact nature of the hydrophobic chains and the surface chemistry of the particles, it is possible to confer a more or less marked hydrophilic character, or a more or less marked lipophilic character, for the modified surface particles present in

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 compositions of the invention. Thus, the particles generally have a lipophilic character all the more strong as chains of hydrophobic nature have a high number of carbon atoms and the number of chains linked to the surface of the particles is important. It is also noted that immobilization of the hydrophobic chains on the surface of the particle inducing a reduction in the charge of the system (particle + chains) tends to increase the lipophilic character of the particles. The hydrophilicity of the modified surface particles present in the compositions of the invention is often all the more important that the linked chains have a low carbon number, that the number of linked chains is reduced, and that the particle retains a charge. notable in the presence of linked groups.

 Preferably, the compositions of the invention comprise particles of modified surface where the bonds between hydrophobic chains and the surface of the particles are all provided by the same type of bond, generally by complexing bond. However, the bonds between the surface of the particles and the hydrophobic chains can be of different nature within the same surfactant of solid character according to the invention. Next to chains fixed by complexing bond can thus coexist for example hydrophobic chains linked in a less strong way to the surface, in particular by electrostatic bonds or by hydrogen bonds, or even, in certain cases, chains linked by covalent bonds.

 Whatever the exact nature of the bonds used to ensure cohesion between the hydrophobic chains and the surface of the particles, it is preferred that the connections between the hydrophobic chains and the particles present in the compositions of the invention are distributed in a non-homogeneous manner over the surface of said particle, so as to define a first zone of generally hydrophilic character and a second zone of generally hydrophobic character.

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 Thus, in a particularly advantageous manner, the modified surface particles present in the compositions of the invention are such that they can each be divided by a plane of cross section into two surfaces Si and 82 such that: (i) Each of the surfaces If and 82 represents at least 20% of the total surface of the particle; and (ii) The surface density of organic chains linked to 82 is greater than at least 5 times the surface density of chains of hydrophobic nature linked to Si.

 Whatever the exact structure of the particles which they contain, the compositions of the invention specifically have a pronounced emulsifying character. This marked emulsifying character can be demonstrated by the fact that they are capable of emulsifying water / oil systems in the form of stabilized emulsions having a high content of dispersed phase and a small average drop size.

 Thus, the compositions of the invention are generally capable of emulsifying in the form of stabilized reverse emulsions of water / oil systems, and they can in particular be used in this context to form emulsions of the water in vegetable oil or water in oil type. of silicone, with a high content of dispersed aqueous phase, that is to say specifically having a content of aqueous phase at least equal to 40%, advantageously greater than or equal to 50%, or even greater than or equal to 60% in certain cases.

 The use of the compositions of the invention for the emulsification of such water / oil systems in the form of reverse emulsions makes it possible, subject to sufficiently pushing the emulsification conditions, to obtain, for these stabilized reverse emulsions, average drop sizes less than or equal to 5 microns. Surprisingly, while average drop sizes of the order of 5 microns are generally difficult to access with usual emulsifying compositions,

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 compositions of the invention allow in certain cases to obtain sizes less than or equal to 3 microns, advantageously less than 2 microns and, in a particularly advantageous manner, of the order of a micron.

 Furthermore, the emulsifying compositions of the invention generally make it possible to emulsify water / oil systems in the form of stabilized direct (oil in water) emulsions having a dispersed phase content which may be greater than 40%, of preferably greater than 50%, or even greater than 60% or even 70%. Subject to sufficiently pushing the emulsification conditions, the size of the drops present in the direct emulsions obtained using the emulsifying compositions of the invention is generally less than or equal to 10 microns, most often less than or equal to 5 microns. Advantageously, it can be less than or equal to 3 microns, and preferably less than or equal to 2 microns, or even 1 micron.

 The emulsifying compositions of the invention may be based on several types of particles of nanometric dimensions and / or of chains of hydrophobic nature. Therefore, they can for example comprise a single type of surfactant of solid character as defined above, but they can also comprise a mixture of several types of these surfactants of solid character, and in particular surfactants of solid character having lengths and / or mainly hydrophobic chain natures, or else a mixture of surfactants of solid nature based on solid particles of different chemical natures. In the context of this type of mixture, the association, generally within the same composition of surfactants formed of solid particles with surface charges of opposite signs, is avoided, but such an association is not however excluded from the scope of the present invention.

 Depending on the exact nature of the solid particle and the hydrophobic chains used, the emulsifying compositions of the present invention can be formulated in various ways.

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 However, taking into account the specificity of the surfactants having a solid character of the present invention, the emulsifying compositions comprising these particles of modified surface are advantageously, in the general case, in the form of an emulsion of oil-in-water type, or water in oil, said particles of nanometric dimensions to the surface of which the organic chains of hydrophobic nature are bonded being located at least partially located at the water / oil type interfaces of said emulsion. Generally, the particles of nanometric dimensions of modified surface are mainly located at the water / oil type interfaces of the emulsion, that is to say that at least 50%, preferably at least 60%, advantageously at least 70%, and even more preferably at least 80% of these particles are located at the interfaces. Thus, it may be emulsions stabilized by surfactants of solid character according to the invention.

 The average size of the drops present in the emulsifying compositions of the invention in the form of emulsions is generally between 0.1! lm and 20! lm, with a distribution of these homodisperse or polydisperse drops. The average size of the drops is preferably less than or equal to 10! lm, preferably at most 5! read. Particularly advantageously, this average drop size is between 0.5! lm and 3! lm, preferably between 0.5 and 2! lm.

 The concentration of modified surface solid particles within this emulsion can be characterized by a rate of recovery of the drops of the emulsion. This recovery rate is defined by the ratio of the portion of the total surface of the drops occupied by the particles on the total surface developed by the drops of the emulsion. Advantageously, this recovery rate of the drops of the emulsion is between 20% and 100%. Preferably, it is greater than 50%, and particularly preferably, greater than 80%.

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 Furthermore, it should be noted that in addition to the particles of surfactant type having a solid character ensuring the stabilization at the liquid / liquid interfaces, the emulsifying compositions of the invention taking the form of emulsions may also contain surface particles. modified not present at these interfaces, and in particular at interfaces of the water / air or oil / air type, or even within the continuous and dispersed phases.

 Overall, taking into account all of the modified surface particles present in the emulsion, it is possible to define a theoretical incorporation rate of the particles, defined by the ratio of the total surface that the solid particles are theoretically capable of covering. present within the emulsion on the total theoretical surface developed by the drops of the emulsion. For this calculation of the theoretical total surface developed by the drops of the emulsion, it is assumed that the emulsion is of monodispersed distribution, with a diameter of drops equal to the average diameter of the drops present. Given this definition, this theoretical rate may be greater than 100%. Preferably, the concentration of modified surface particles within the emulsion is such that this theoretical incorporation rate is between 20% and 300% and advantageously between 50 and 200%.

 The presence of these modified surface particles at the liquid / liquid interfaces allows effective stabilization of the emulsifying composition in the form of an emulsion. Thus, it is generally found that the stability is such that after storage for a period of 7 days, advantageously for a period which can range at least up to 30 days, the composition remains in the form of an emulsion.

 Furthermore, this stabilized emulsion is specifically a composition which can play the role of a stabilizing composition, to ensure the stabilization of emulsions of the oil in water or water in oil type.

However, taking into account the dilution introduced in this type of operation, these emulsifying compositions in the form of emulsions are, in this case, generally used in high proportions, generally at the right level.

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 from 10% to 80% by volume relative to the total volume of the emulsion to be stabilized, and advantageously at a rate of 10% to 50% by volume.

 Therefore, when possible, it is preferred to use the surfactants having a solid character of the invention in the form of a concentrated formulation preferably having a solid content greater than 5% by mass, advantageously greater than 8 % by mass, and preferably greater than 10% by mass.

 This concentrated formulation can for example be formed by an ultracentrifugation pellet obtained for example by ultracentrifugation, or even by concentration by slow evaporation, of an emulsifying composition in the form of an emulsion as defined above.

 However, it should be emphasized that this type of formulation cannot be envisaged with all the types of modified surface particles of the invention. In fact, within this type of concentrated formulation, the solid particles are sufficiently close together that one can observe phenomena of interparticle agglomeration.

 Therefore, the modified surface particles used in this type of concentrated formulations are preferably particles based on calcium phosphate, vanadium phosphate or rare earth vanadate, advantageously having high surface charges, for which these phenomena of re-agglomeration are minimized.

However, the concentrated emulsifying formulations of the invention cannot be limited to these particular compounds.

 In addition to these surface-modified particles, the emulsifying compositions of the invention in the form of concentrated formulations generally contain water and liquid compounds which are not very immiscible with water, such as vegetable oils, silicone oils or hydrocarbons. . The ratio of the content of water and hydrophobic liquid compounds in these compositions is variable to a large extent.

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 Thus, in the case of a concentrated formulation obtained by ultracentrifugation or by concentration by evaporation of a mother emulsion, this ratio varies according to the nature of said mother emulsion.

Generally, the volume ratio of the phase initially corresponding to the dispersed phase of the mother emulsion to the phase initially corresponding to the continuous phase of the mother emulsion is between 0.01 and 0.8.

Advantageously, this volume ratio is at least equal to 0.2, and preferably at least equal to 0.4.

 The concentrated formulations defined above have significant emulsifying properties. They are capable of stabilizing water-in-oil or oil-in-water emulsions, or even multiple emulsions with good stability over time. In general, this type of concentrated emulsifying composition is used at a rate of 10 to 200% by mass relative to the mass of the dispersed phase of the emulsion to be stabilized. Advantageously, these formulations are used in an amount of 10 to 100% by mass and preferably in an amount of 10 to 50% by mass relative to the mass of the dispersed phase.

 The emulsifying compositions comprising the modified surface particles of the invention can also be in the form of dispersions with a high solid content having, where appropriate, a solid content of between 10 and 90% by mass.

 These concentrated dispersions are generally formed from a dispersion of surface particles modified according to the invention in a continuous phase of hydrophilic or hydrophobic character, where said continuous phase generally represents at least 50% of the volume of the dispersion.

 The stabilized emulsions obtained by using the emulsifying compositions of the invention, whether in the form of emulsions of concentrated formulations or of dispersions with a high solid content, can use numerous hydrophobic phases.

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 compounds, such as vegetable oils, mineral oils, aromatic solvents or even water-insoluble ketones.

 The nature of the hydrophobic and hydrophilic phases used within the emulsions stabilized by using an emulsifying composition according to the invention is not necessarily dependent on the nature of the hydrophilic and hydrophobic phases present within the emulsifying composition. Thus, an emulsifying composition comprising a particular hydrophobic phase may in particular be used to ensure the stabilization of an emulsion comprising another type of oil, insofar as this oil is soluble to that present in the emulsifying composition.

 Finally, in the case of the use of certain particles, the emulsifying compositions of the invention can be in the form of a solid powder, advantageously essentially consisting of surfactants of solid character according to the invention, said agents solid surfactants in this case preferably based on calcium phosphate, rare earth phosphate or rare earth vanadate, these agents generally being redispersible with a low rate of interparticle agglomeration in aqueous, hydrophobic media, or in biphasic water / oil media.

 According to another aspect, the present invention also relates to a process for the preparation of emulsifying compositions as defined above.

 This process for preparing an emulsifying composition according to the invention is characterized in that it comprises a step consisting in forming an emulsion from an aqueous phase and from a hydrophobic phase in the presence of a molecular surfactant and colloidal particles based on a phosphate or a metallic vanadate, of nanometric dimensions, and capable of associating with said molecular surfactants by complexing bond, by electrostatic bond or by hydrogen bond, these

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 particles generally having a hydrophilic surface, and advantageously a non-zero surface charge.

 This step of forming the emulsion must specifically be carried out so as to anchor the colloidal particles associated with the molecular surfactants at the water / oil interfaces of the emulsion, while avoiding the transfer of these colloidal particles associated with the molecular surfactant to the hydrophobic phase. This anchoring induces for the particles a zone oriented towards the hydrophobic phase and a zone oriented towards the hydrophilic phase.

 The specific anchoring of the particles at the interfaces thus produced can be viewed for example by transmission cryo-microscopy on frozen samples, according to the Dubochet method, consisting in producing a thin film of thickness between 50 and 100 nm by immersing a pierced support in the emulsion, and immersing the film thus obtained in liquid ethane or liquid nitrogen, which preserves a state of dispersion of the particles representative of that present in the initial emulsion.

 Thus, according to an advantageous embodiment, the method for preparing an emulsifying composition according to the invention comprises the steps consisting in: (a) forming a hydrophobic phase and an aqueous colloidal dispersion of particles of nanometric dimensions based on 'a metal compound chosen from a phosphate or a vanadate, said hydrophobic phase or said aqueous dispersion comprising a molecular surfactant capable of associating, by complexation, by electrostatic interaction or by hydrogen bonding, with the colloidal particles; (b) mixing by adding the hydrophobic phase to the aqueous dispersion or by adding the aqueous dispersion to the hydrophobic phase; and (c) subjecting the mixture obtained to an emulsification.

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 Advantageously, the colloidal particles used in this embodiment of the process of the invention are in the form of aqueous colloidal dispersions preferably having monodispersed particle size distributions, and advantageously characterized by an interparticle agglomeration rate of less than 20% by number, preferably less than 5%, and within which the average hydrodynamic diameter of the particles is advantageously between 2 and 100 nm in the case of particles of isotropic morphology and between 5 and 250 nm in the case of particles of anisotropic morphology .

 The particles of step (a) preferably consist at least partially of a calcium phosphate, a rare earth phosphate or a rare earth vanadate, and they can have various chemical groups on the surface, advantageously groups of the metal cation type or of the (Met) -O (H) ... H + or (Met) -OH ... OH-- type (where Met denotes a metal). The particles may also have surfactants such as citrate ions, acetate ions or amino acids, generally linked to the particle via a metal cation, most often by complexing bond.

21 - mettre en contact, en solution aqueuse, une source de cations Ca2+, une source d'anions PC'et un acide aminé, à un pH compris entre 5 et 10, avec des quantités respectives de source de Ca2+ et de source d'anions P043telles que le rapport molaire Ca/P varie entre 1 et 3,5, et avec une quantité d'acide aminé telle que le rapport molaire acide aminé 1 Ca varie entre 0,3 et 2,5 ; et The aqueous colloidal dispersions based on calcium phosphate used in the context of the process of the invention can typically be obtained according to a process comprising the steps consisting in:

21 - bringing into contact, in aqueous solution, a source of Ca2 + cations, a source of PC anions and an amino acid, at a pH of between 5 and 10, with respective amounts of Ca2 + source and of P043 anions such that the Ca / P molar ratio varies between 1 and 3.5, and with an amount of amino acid such that the amino acid 1 Ca molar ratio varies between 0.3 and 2.5; and

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 - allow the medium obtained to mature at a temperature between 15 ° C. and 150 ° C. until a colloidal dispersion is obtained, which can optionally be washed by ultrafiltration.

 Colloidal dispersions based on rare earth phosphate (respectively vanadates) of rare earth which can be used in the context of the implementation of the process of the invention can typically be obtained according to a process comprising the steps consisting in: - forming an aqueous mixture comprising a rare earth salt and a complexing agent of said rare earth, having a pK greater than 2.5, preferably at least 3, K being the dissociation constant of the complex, this complexing agent being preferably a polyacid alcohol such as citric acid; and - adding a base and a source of phosphate ions, hydrogen phosphate (respectively a source of vanadate ions) to the medium, until a pH generally between 9 and 12.5 is obtained, then bringing the medium to a temperature between 60 and 180 C, whereby a colloidal dispersion is obtained, which can optionally be washed by ultrafiltration.

 The hydrophobic phase used in the process of the invention consists of a liquid or a mixture of organic liquids at least sparingly soluble in water, and advantageously insoluble in water, and which can be of a nature extremely varied.

 Thus, it may especially be an inert aliphatic and / or cycloaliphatic hydrocarbon, or a mixture of such compounds, such as for example a mineral spirits or petroleum spirits which may contain, if necessary, aromatic compounds. . Mention may also be made, by way of indication, of hexane, heptane, octane, nonane, decane, cyclohexane, cyclopentane, cycloheptan and liquid naphthenes as compounds.

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 particularly suitable. Aromatic solvents such as benzene, toluene, ethylbenzene and xylenes are also suitable, as well as petroleum fractions of the ISOPAR or SOLVESSO type (trademarks registered by the company EXXON), in particular SOLVESSO 100, which essentially contains a mixture of methylethyl -and trimethyl-benzene, and SOLVESSO 150 which contains a mixture of alkyl benzenes, in particular dimethylethyl benzene and tetramethyl benzene.

 It is also possible to use chlorinated hydrocarbons such as chloro or dichlorobenzene, chlorotoluene, as well as aliphatic and cycloaliphatic ethers such as diisopropyl ether, dibutyl ether or aliphatic and cycloaliphatic ketones such as as methyl isobutyl ketone, dibutyl ketone, or mesityl oxide.

 Ketones immiscible with water can also be used.

 Esters can also be considered. Mention may be made, as esters which can be used, in particular those resulting from the reaction of acids with alcohols having from 1 to 8 carbon atoms, and in particular secondary alcohol palmitates such as isopropanol. The acids from which these esters are derived can be aliphatic carboxylic acids, aliphatic sulfonic acids, aliphatic phosphonic acids, alkylarylsulfonic acids, and alkylarylphosphonic acids having about 10 to about 40 carbon atoms, whether natural or synthetic. . By way of example, mention may be made of tall oil fatty acids, coconut oil, soybean, tallow, linseed oil, oleic acid, linoleic acid, stearic acid and its isomers , pelargonic acid, capric acid, auric acid, myristic acid, dodecylbenzenesulfonic acid, 2-ethylhexanoic acid, naphthenic acid, hexoic acid, toluenesulfonic acid , toluenephosphonic acid, lauryl-sulfonic acid, lauryl-phosphonic acid, palmityl-sulfonic acid, and palmityl-phosphonic acid. The mixtures of these different compounds are particularly suitable hydrophobic phases.

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soja, les huiles de lin, les huiles de colza, ou encore les huiles de coco. As a particularly advantageous hydrophobic phase in the context of the invention, mention may be made of vegetable oils, such as

soybeans, linseed oils, rapeseed oils, or even coconut oils.

 The silicone oils are also hydrophobic compounds advantageously used.

 It should be noted that the exact nature of the hydrophobic phase used in the process is to be adapted as a function of the nature of the molecular surfactant used. Indeed, it should in particular be emphasized that, in the process of the invention, the affinity between the hydrophobic phase and the molecular surfactant used must be sufficiently low so that the anchoring of the particles at the interfaces is effectively observed of the emulsion produced.

 In other words, the hydrophobic phase and the molecular ionic surfactant used in the process of the invention are generally chosen so that said molecular surfactant does not lead, in the absence of colloidal particles, to an optimal emulsion, in particular in terms of stability, of a hydrophilic phase with the hydrophobic phase used.

 In general, the hydrophobic phase and the hydrophobic chain of the molecular ionic surfactant used are chosen so that said hydrophobic phase has poor compatibility with the hydrophobic chain of the molecular surfactant used. With regard to the choice of the hydrophobic phase and of the molecular surfactant, a person skilled in the art will therefore be able to use the concept based on the parameters of volume and solubility.

 Indeed, a hydrophobic phase can be characterized by three solubility parameters 8D, 8P and 8H, defined from the cohesion energy corresponding to the intermolecular attraction forces. 8D, 8P and 8H represent respectively the parameters corresponding to the London dispersion energy, the Keesom polarity energy and to a parameter linked to the hydrogen bonding forces. On this subject, one can in particular refer to the article by J. Hidelbrand, in the Journal of the American Chemical Society,

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 volume 38, page 1452, (1916) or to the work of J. Hidelbrand et al., "The solubility of non electrolytes", 3rd edition, Reinhold, New York, (1949).

 In general, a hydrophobic chain will be all the less soluble in a hydrophobic phase that the solubility parameters 8D, 8P and 8H of this chain will be different from those of the hydrophobic phase.

 The nature of the molecular surfactant used is for its part to be adapted as a function of the nature of the emulsion (direct or reverse) envisaged and of the nature (size, composition, etc.) of the particles used.

However, in the general case, the molecular surfactants used generally have a molecular weight of from 100 g / mol to 10,000 g / mol, and advantageously from 100 g / mol and 5,000 g / mol. These molecular surfactants can for example be surfactants of the oligomer or block copolymer type.

 Furthermore, the molecular surfactants used specifically have a chemical group capable of complexing the metal cations present on the surface of the particles used.

 In fact, the aim of the process of the invention is specifically to formulate an emulsifying composition comprising surfactants of a solid nature within the meaning of the invention where the fixing of the hydrophobic chains to the surface of a particle is ensured by strong complexation.

 Thus, in the general case, so as in particular to ensure optimum cohesion between the particle and the molecular surfactant within the emulsifying composition obtained, the molecular surfactants used are preferably molecular surfactants with complexing polar head which can, for example, be surfactants with polar head carboxylic acid or carboxylate, surfactants with polar head phosphoric acid or phosphate, surfactants with polar head sulfosuccinic acid or sulfosuccinate, or surfactants with polar head sulfonic acid or sulfonate. Advantageously, these surfactants can be chosen from

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 alkylcarboxylates or carboxylic acids containing from 4 to 20 carbon atoms, preferably from 6 to 18 carbon atoms, or alkylphosphates containing from 4 to 20 carbon atoms, and preferably from 6 to 18 carbon atoms.

 These molecular surfactants can also be chosen from polyoxyethylenated alkyl ethers of carboxylic acids of formula Ra- (OC2H4) n-0-Rb, where Ra is a linear or branched alkyl having 4 to 20 carbon atoms, n is an integer between 1 and 12 and Rb is a carboxylic acid group such as CH2-COOH, or mixtures of such compounds, such as those sold under the brand AKIPO by the company Kao Chemicals.

ou encore les phosphates de dialcoyle poyoxyéthylénés de formule :

Dans les formules ci-dessus, Rc, Rd, Re identiques ou différents représentent un radical alkyl linéaire ou ramifié possédant de 2 à 20 atomes de carbone ; un radical phényle ; un radical alkylaryl, plus particulièrement un radical alkylphényl, avec notamment une chaîne alkyle possédant de 8 à 12 atomes de carbone ; un radical arylalkyle, plus particulièrement un radical phénylaryl ; n représente un nombre entier pouvant varier de 2 à 12 ; Mi représente un atome d'hydrogène, de sodium ou de potassium. Les radicaux Rc, Rd et Re peuvent The molecular surfactant can also be chosen from polyoxyethylenated alkyl ethers phosphates. By "polyoxyethylenated alkyl ethers phosphates" is meant the polyoxyethylenated alkyl phosphates of formula:

or also the poyoxyethylenated dialkyl phosphates of formula:

In the above formulas, Rc, Rd, Re identical or different represent a linear or branched alkyl radical having from 2 to 20 carbon atoms; a phenyl radical; an alkylaryl radical, more particularly an alkylphenyl radical, with in particular an alkyl chain having from 8 to 12 carbon atoms; an arylalkyl radical, more particularly a phenylaryl radical; n represents an integer which can vary from 2 to 12; Mi represents a hydrogen, sodium or potassium atom. The radicals Rc, Rd and Re can

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 be in particular hexyl, octyl, decyl, dodecyl, oleyl, or nonylphenyl radicals.

-les poly-oxy-ethylène tri-decyl ether phosphate Rhodafac RS 710 ou RS 410 - les poly-oxy-ethylène oleocétyl ether phosphate Rhodaface PA 35 - les poly-oxy-ethylène nonylphenyl ether phosphate Rhodafaco PA 17 - les poly-oxy-ethylène nonyl (ramifié) ether phosphate Rhodafac RE 610
Le tensioactif moléculaire peut également être choisi parmi les diakylsulfosuccinates c'est à dire les composés de formule R6-O-C (O)-CH2CH (S03M2)-C (O)-O-R7 dans laquelle R6 et R7, identiques ou différents représentent un radical alkyl de C4 à C14 par exemple et M2 est un métal alcalin ou un hydrogène. Comme composés de ce type, on peut mentionner ceux commercialisés sous la marque AerosolE par la société Cyanamid. On peut également utiliser des copolymères séquencés Polyacrylate-polystyrène, ou tout copolymère séquencé comprenant une partie hydrophile comportant des fonctions complexantes, de préférence carboxylates et/ou phosphates. As an example of this type of amphiphilic compound, mention may be made of those sold under the brands Lubrophos and Rhodaface by Rhodia, and in particular the products below: - the poly-oxy-ethylene alkyl (C8-C10) ether phosphates Rhodafaco RA 600

- poly-oxy-ethylene tri-decyl ether phosphate Rhodafac RS 710 or RS 410 - poly-oxy-ethylene oleocetyl ether phosphate Rhodaface PA 35 - poly-oxy-ethylene nonylphenyl ether phosphate Rhodafaco PA 17 - poly-oxy- ethylene nonyl (branched) ether phosphate Rhodafac RE 610
The molecular surfactant can also be chosen from diakylsulfosuccinates, that is to say the compounds of formula R6-OC (O) -CH2CH (S03M2) -C (O) -O-R7 in which R6 and R7, which are identical or different, represent a alkyl radical from C4 to C14 for example and M2 is an alkali metal or hydrogen. As compounds of this type, mention may be made of those sold under the brand AerosolE by the company Cyanamid. Polyacrylate-polystyrene block copolymers can also be used, or any block copolymer comprising a hydrophilic part comprising complexing functions, preferably carboxylates and / or phosphates.

 In the particular context of the implementation, in the process of the invention, of particles based on calcium phosphate, based on a rare earth phosphate, or based on a rare earth vanadate, the agents molecular surfactants used are advantageously surfactants whose polar head is a group chosen from a carboxylate group or a phosphate group.

 Furthermore, and whatever the nature of the emulsion and of the molecular surfactant (s) used, the total concentration of molecular ionic surfactant within the hydrophobic or hydrophilic phase is preferably such that the molecular ionic surfactant is used in the right way

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 from 0.2 to 20% by mass relative to the weight of the dispersed phase of the emulsion obtained, and advantageously at a rate of 0.5 to 10% by mass. It is moreover preferred that the total amount of molecular ionic surfactant within the hydrophobic or hydrophilic phase is such that the molar ratio of the amount of molecular ionic surfactant relative to the amount of metal present in the phosphates and / or vanadates constituting the particles. is between 0.02 and 2, and preferably between 0.05 and 1.

 Depending on the properties sought for the emulsifying composition obtained in fine, it may be necessary to choose a hydrophobic phase, a molecular surfactant or specific colloidal particles. Depending on the choice of a first parameter, for example the chemical nature of the colloidal particle used, it is the skill of the person skilled in the art to adapt the other parameters, in particular the nature of the hydrophobic phase and of the molecular surfactants used , as well as the different concentrations and the hydrophobic phase / hydrophilic phase ratio used.

 It should be noted that these different parameters must be adapted on a case-by-case basis. However, in the general case, the concentration of the colloidal dispersion used is generally such that it corresponds to a theoretical coverage rate of the drops in the emulsion obtained at the end of step (c), defined by the ratio of the surface that are theoretically capable of covering the colloidal particles used on the total surface developed by the drops of the emulsion, between 100 and 600%, preferably between 100 and 400%, and advantageously between 100 and 300%.

In other words, an excess of particles of nanometric dimensions is therefore generally used in the process of the invention.

 Consequently, the concentration of colloidal particles in the colloidal dispersions used is generally between 1020 and 4. 1021 particles per liter and preferably between 2.1020 and 1021 particles per liter.

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 The ratio of the volume of the dispersed phase to the total volume of the emulsion used is generally between 5 and 90%, preferably between 10 and 80%, and particularly advantageously between 15 and 80%.

 Step (c) leading to the formation of the emulsion from the hydrophobic and aqueous phases is generally carried out by dispersion or microfluidization at room temperature, in particular by using a fast disperser of the Ultraturaxt type. In this case, the emulsion is generally obtained by subjecting the mixture resulting from step (b) to a dispersion under shear, generally carried out for a period of 15 seconds to 1 hour, and preferably for a period of 30 seconds to 2 minutes, with an agitation speed advantageously between 5,000 and 20,000 revolutions per minute.

 This emulsification step (c) leads to a so-called "crude" emulsion, where, given the preferential use of an excess of colloidal particles, a possibly large portion of the colloidal particles may not be located at the interfaces of water / oil type of emulsion.

 Therefore, the crude emulsion obtained at the end of step (c) can be subjected to a subsequent centrifugation step (d). Where appropriate, this centrifugation is carried out at a speed advantageously between 1,000 and 5,000 revolutions per minute and for a period ranging from 2 minutes to 30 minutes.

 Generally, this centrifugation leads to the obtaining of 3 phases: the upper phase of the type of the continuous phase of the raw emulsion of step (c), the lower phase constituting the centrifugation pellet and generally comprising the colloidal particles put in excess, and an intermediate phase consisting of a stabilized emulsion of improved quality. It is this stabilized emulsion constituting the intermediate phase which is, if necessary, recovered at the end of step (d).

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 Whether this centrifugation step is carried out or not, the emulsion obtained can then be subjected to a step (e) of heat treatment aimed at strengthening the interactions between particles and molecular surfactants.

Preferably, this heat treatment step is carried out by bringing the emulsion obtained at the end of the preceding steps to a temperature between 40 ° C. and 100 ° C., and preferably between 500 ° C. and 90 ° C., for a period ranging from 30 minutes. at 24 hours, and advantageously between 2 hours and 5 hours. During this heat treatment step, the emulsion can be brought to said temperature, either directly, or by a gradual rise in temperature ranging, if necessary, from 40 ° C. per minute to 0.2 ° C. per minute.

 The emulsion obtained at the end of step (c) and any steps (d) and / or (e) can be used as an emulsifying composition according to the invention. According to a variant, this emulsion can also be subjected in certain cases to a step (f) of ultracentrifugation so as to obtain a concentrated emulsifying formulation in the form of an ultracentrifugation pellet.

Preferably, the ultracentrifugation of step (f) is carried out at the rate of 5,000 to 30,000 revolutions per minute, advantageously at the rate of 3,000 to 25,000 revolutions per minute, for a period generally ranging from 1 to 8 hours. , and preferably for a period ranging from 2 to 6 hours.

 The ultracentrifugation pellet obtained is then generally characterized by a solid content greater than 5% by mass, and preferably greater than 8% by mass. The water and oil contents vary as a function of the nature of the emulsion subjected to the ultracentrifugation. In general, the volume ratio of the phase corresponding to the dispersed phase of the original emulsion to the volume of the phase corresponding to the continuous phase of the original emulsion varies between 0.01 and 0.8 , advantageously between 0.1 and 0.8 and preferably between 0.2 and 0.8.

 However, it is important to note that, as already pointed out, this ultracentrifugation step can lead, within the framework of the use of certain colloidal particles, to phenomena

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 of interparticle agglomerations liable to harm the emulsifying properties of the ultracentrifugation pellet obtained. Therefore, within the framework of the implementation of step (f), it is preferred that the particles used in the process are particles based on calcium phosphate of apatite structure, or also based on phosphate or rare earth vanadates, and having high surface charges.

 The formulations obtained at the end of step (c), and any steps (d), (e) and / or (f) may also be subjected to a step (g) comprising the steps consisting in: ( gi) adding a solvent or water to the formulation, the mass of the added solvent or of the added water being between 0.1 and 10 times the mass of the formulation used; and (g2) concentrating the mixture obtained by filtration or by evaporation, whereby a solid-enriched phase is obtained.

 Advantageously, this step (g) is carried out several times with successive solvents of increasing polarities, whereby a concentrated dispersion of modified surface particles of surfactant type with a solid character is obtained in fine in an essentially hydrophilic phase.

 Advantageously, it is possible, during these successive treatments, to use solvents of low polarity, such as heptane or hexane, then solvents of greater polarity, such as chloroform, and finally solvents of even greater polarity, such as water-methanol mixtures.

 Similarly, step (g) can be carried out several times with successive solvents of increasing hydrophobicities, whereby a concentrated dispersion of surface-modified particles of surfactant type having a solid character is obtained in an essentially hydrophobic phase. .

 During these various successive stages, the obtaining of a phase enriched in solid can be carried out, in the stages of type (g2), by

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 filtration, or by any other solid / liquid separation means known to those skilled in the art.

 In general, the content of continuous phase in the concentrated dispersion obtained is at least 50% by volume. The solid content is generally between 10 and 90% by mass.

 Alternatively, in certain particular cases, the emulsion obtained at the end of step (c) and any steps (d) and / or (e) can also be subjected to a step (f) of drying to low temperature, that is to say less than 150 ° C., whereby the emulsifying composition is obtained in the form of a solid. This step (f) is generally carried out at a temperature of between 20 and 120 ° C., and it advantageously comprises a step of prior dilution of the emulsion obtained at the end of step (c) and any steps (d) and / or (e), by adding an aqueous phase and / or a hydrophobic phase.

 In this context, it is generally preferred to use, as hydrophobic phase in the process of the invention, an oil having a low boiling point, advantageously less than 1200C and more preferably less than 90 C. Furthermore, the particles of nanometric dimensions used to form compositions in the form of a redispersible solid, are generally particles having in themselves a redispersible character, such as particles having high surface charges, based on calcium phosphate, or based on phosphate or rare earth vanadates.

 The various preferred variants set out above with regard to the method of preparation of an emulsifying composition according to the invention cannot in any way limit the process of the invention to these particular variants.

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 Thus, subject to adapting the nature of the hydrophobic phase and of the molecular surfactant used, most colloidal particles based on phosphate or metallic vanadate of nanometric dimensions can be used in the process of the invention.

 More generally, depending on the exact nature of the colloidal particles of nanometric dimensions used and / or the molecular ionic surfactant or the hydrophobic phase used, it is the skill of the person skilled in the art to adapt the steps (a), (b) and (c). The only condition to be observed is to form an emulsion in the presence of said particles and of said molecular surfactant while promoting interactions between particles and molecular surfactants and avoiding the transfer of particles complexed by molecular surfactants to the hydrophobic phase.

 Due to their emulsifying nature and the presence of solid particles within their composition, and whatever their method of production and the exact nature of their constituents, the emulsifying compositions of the invention can be used in many areas of application.

 Thus, the emulsifying compositions of the invention can in particular be used for the formulation of detergent compositions especially suitable for cleaning hard surfaces, where the combination of the emulsifying nature and the presence of solid particles induces both mechanical abrasion and a emulsification of hydrophobic stains.

 Furthermore, the emulsifying compositions of the invention can have advantageous physicochemical properties due to the presence of solid particles.

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 As a result, the emulsifying compositions of the invention can in particular be used for the manufacture of films and materials, in particular packaging films. Specifically, the compositions based on metallic phosphates can thus advantageously be used for the production of encapsulation film for the food industry. The compositions comprising phosphate-based particles or rare earth vanadates, known as doped, that is to say having a small amount of cation of europium-type substitutions for example, can for their part be used for the production of films with properties luminescent. The use of solid particles of amphiphilic nature of the invention can also allow the manufacture of films with high mechanical resistance, or even opacifying films.

 In this type of material, the solid particle of amphiphilic nature originating from the emulsifying composition plays both a role linked to its intrinsic physicochemical properties and a role of surfactant linked to its amphiphilic character. Compared to the molecular surfactants conventionally used in the constitution of such materials, the surface-modified particles of the surfactant type of the invention present. moreover the advantage, by their solid nature, of not leading to the phenomena of surface migration generally observed.

amphiphile selon l'invention. The illustrative examples set out below relate to the preparation of emulsifying compositions comprising solid particles with character

amphiphilic according to the invention.

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 Example 1: Preparation of an emulsifying composition comprising lanthanum phosphate particles of amphiphilic nature as surfactants.

(1) preparation of a colloidal dispersion (01) of lanthanum phosphate
To 204 g of demineralized water contained in a beaker with stirring at 25 ° C., 31.4 g of citric acid (i.e. 0.148 mole) were dissolved, then 90.22 g of La (NO 3) 3 to 26 were added 98% in La 2 O 3 (which corresponds to 0.148 mole of La), so as to obtain a molar ratio (citrate / La) of 1 in the solution. The solution was allowed to stir for one hour.

 Then, using a metering pump, with an addition rate of 2 ml per minute, 202 ml of a 3.25 M ammonia solution were added. The mixture was left stirring for 60 minutes afterwards. the end of the addition. A solution (sol) of pH 8.78 was thus obtained.

 An aqueous solution (S2) of ammonium phosphate was also prepared by adding demineralized water to 15.63 g of (NH4) zHPO4 (i.e. 0.118 moles) until a volume of aqueous solution of 300 ml was obtained. .

 The solution (S2) thus obtained was added instantaneously to the solution (sol) of lanthanum nitrate previously prepared, with stirring, so as to obtain a medium characterized by a P / La molar ratio equal to 0.8. The mixture was left stirring for 15 minutes. The pH of the medium obtained was measured equal to 8.76.

 By adding 238.4 g of 4M NaOH solution, the pH of the medium was adjusted to 12, then this medium was placed in a closed enclosure (Parr bomb) which was placed for 16 hours in an oven previously carried at 120 C.

 It was cooled to a temperature of 25 ° C., and the colloidal dispersion obtained was collected. The pH of the dispersion was then adjusted to 10 by addition of 47.8 g of a 4M aqueous solution of nitric acid.

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 The dispersion was then washed 4 times with demineralized water with each time a volume equal to the volume of the dispersion. This washing is carried out by ultrafiltration on a 3 KD membrane.

 The dispersion thus obtained was then concentrated by ultrafiltration at 0.25 M., whereby a dispersion (D1) was produced which has the following characteristics: - Density = 1.04 - LaP04 concentration = 3.13% in mass (Determination by loss on ignition), i.e. a lanthanum concentration of 0.13 mole / kg (or 0.14 mole / L).

 - Average size of colloids: 3 nm (particles essentially all individualized, as visualized by cryo-transmission microscopy).

(2) preparation of the emulsifying composition
Was dissolved in 80 ml of ethyl acetate, 0.8 g of RO 20 VG (mixture of compounds of general formula A- (OC2H4) 2-OCH2COOH or A represents an alkyl chain having from 16 to 18 atoms of carbon, sold under this name by the company Kao Chemicals, this solution was stirred in a closed chamber for 15 minutes.

 20 ml of the colloidal dispersion (D1) were then added to the ethyl acetate solution thus prepared.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 2 minutes at the rate of 11,000 revolutions per minute.

 An emulsion was obtained in the form of a stable gel.

 The size of the drops determined by optical microscopy within this gel is of the order of 0.8 microns.

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 The emulsion obtained can be diluted with water. Thus, it is noted in particular that, if 50 cm3 of water are added to 10 cm3 of said emulsion, and the mixture produced is stirred manually, a stable emulsion is kept.

Example 2: Preparation of an emulsifying composition comprising lanthanum phosphate particles of amphiphilic nature as surfactants.

 3.08 g of RO 20 VG were dissolved in 400 ml of octanol. This solution was stirred in a closed enclosure for 15 minutes.

 100 ml of the colloidal dispersion (D1) were then added to the octanol solution thus prepared.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 1 minute at the rate of 11,000 revolutions per minute.

 An emulsion was obtained in the form of a stable gel, dilutable with water without loss of stability, where the size of the drops determined by optical microscopy is of the order of 1 micron.

 An aliquot of the emulsion obtained was diluted by 10 times its volume of demineralized water. The medium was then allowed to evaporate in an extractor hood at 25 C. After one week, a dry powder was obtained.

 0.05 g of this powder was introduced into a mixture containing 20 mL of water and 20mL of octanol. By stirring, an emulsion was obtained, which was homogenized using an ultraturax disperser for one minute at the rate of 11,000 revolutions per minute. A stable emulsion was obtained, in which the size of the drops determined by optical microscopy is of the order of 8 microns.

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Example 3: Preparation of an emulsifying composition comprising lanthanum phosphate particles of amphiphilic nature as surfactants.

 0.17 g of RO 20 VG was dissolved in 80 ml of rapeseed oil.

 The colloidal dispersion (D1) of Example 1 was then diluted to a concentration of 0.2 mol / liter of lanthanum. 20 ml of this diluted dispersion were added to the rapeseed oil solution prepared above.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 2 minutes at the rate of 11,000 revolutions per minute.

An emulsion dilutable with water was obtained without loss of stability in the form of a stable gel.
The size of the drops determined by optical microscopy is of the order of 5 microns.

Example 4: Preparation of an emulsifying composition comprising calcium phosphate particles of amphiphilic nature as surfactants.

(1) preparation of a colloidal dispersion (D2) of calcium phosphate stabilized by lysine
A solution A was prepared by placing in a beaker 50.8 ml of 0.98 M phosphoric acid (ie 50 millimoles of phosphorus), diluted with demineralized water to a volume of 75 ml. The pH was adjusted to a value of 9 by adding 10.5 M ammonia.

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 A solution B was prepared by mixing, with stirring until complete dissolution, 24.6 g of Ca (NOs) 2 (i.e. 150 millimoles of Ca), 43.92 g of lysine (i.e. 300 millimoles), and l demineralized water up to a volume of 75 mL.

 Solution A was added instantaneously to solution B at 25 C, so as to obtain a medium characterized by a molar ratio (Ca: P) equal to 3. The pH was adjusted to 9 with concentrated ammonia 10.5 M, then the medium was allowed to stir for 15 minutes.

 The mixture obtained was transferred to a closed enclosure (Parr bomb) which was placed for 16 hours in an oven previously heated to 800C.

 At the end of this temperature ripening, a colloidal dispersion was obtained, which has a concentration (determined by loss on ignition) of 8.12% in solid. By transmission cryo-microscopy, individualized colloids were visualized for this dispersion. These colloids consist of a population of objects having an anisotropic morphology with an average length of 50 nm and a second population with a more isotropic morphology, of spheres type, with an average diameter of 10 nm.

 On an aliquot of 100 ml of the dispersion obtained, an ultrafiltration washing was carried out in Amicon type cells equipped with 3 KD membranes. The dispersion is washed with 4 equivalent volumes of demineralized water. After this washing, the volume of the dispersion is 100 ml and has a concentration of 4.45% in solid. The dispersion was concentrated to a final volume of 50 ml, a dispersion (D2) of density equal to 1.11 and having a loss on ignition of 7.78% was then obtained.

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(2) preparation of the emulsifying composition
0.0145 g of CH3 (CH2) 6COOH was dissolved in 20 ml of rapeseed oil.

 5 ml of the colloidal dispersion (D2) were then added to the rapeseed oil solution thus prepared.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 2 minutes at the rate of 11,000 revolutions per minute.

 A stable emulsion was obtained, dilutable with water without loss of stability, within which the size of the drops determined by optical microscopy is of the order of 20 microns.

Example 5: Preparation of an emulsifying composition comprising calcium phosphate particles of amphiphilic nature as surfactants.

 0.217 g of RO 90 (surfactant sold by Kao Chemicals) was dissolved in 20 ml of rapeseed oil.

 5 ml of the colloidal dispersion (D2) were then added to the solution thus prepared.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 2 minutes at the rate of 11,000 revolutions per minute.

 A stable emulsion was obtained, where the size of the drops determined by optical microscopy is of the order of 2 microns.

 This emulsion can be diluted with rapeseed oil without loss of stability: if 25 ml of rapeseed oil are added to 5 ml of the emulsion, a stable emulsion is kept.

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Example 6: Preparation of an emulsifying composition comprising calcium phosphate particles of amphiphilic nature as surfactants.

(1) preparation of a colloidal dispersion (D3) of calcium phosphate stabilized by alanine
A solution (A ') was prepared by placing in a beaker 50.8 ml of 0.98 M phosphoric acid (ie 50 millimoles of phosphorus), diluted with demineralized water to a volume of 60 ml. The pH was adjusted to 9.1 by adding 12 ml of 10.5 M ammonia. Then demineralized water was added until a volume of 75 ml was obtained.

 A solution (B ') was prepared by mixing, with stirring until complete dissolution, 24.6 g of Ca (NO 3) 2 (i.e. 150 millimoles of Ca), 26.6 g of alanine, and 60 ml of 'water. It was adjusted to pH 9 by the addition of 6 ml of 10.5 M ammonia. Demineralized water was then added until a volume of 75 ml was obtained.

 The solution (A ') was added instantaneously to the solution (B') at 25 C, so as to obtain a medium characterized by a molar ratio (Ca: P) equal to 3 and a pH of 8.85. The pH was adjusted to 9 with 10.5 M concentrated ammonia, then the medium was allowed to stir for 15 minutes.

 The mixture obtained was transferred to a closed enclosure (Parr bomb) which was placed for 16 hours in an oven previously brought to a temperature of 50 C.

 At the end of this temperature ripening, a colloidal dispersion was obtained, which has a concentration of 1 mole per liter of calcium. By transmission cryo-microscopy, we visualized for this dispersion well individualized colloids made up of a population

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(2) preparation of the emulsifying composition
1.085 g of RO 90 were dissolved in 20 ml of 47 V 100 silicone oil (Rhodia).

 5 ml of the colloidal dispersion (D3) were then added to the silicone oil solution thus prepared.

 The mixture obtained was then emulsified using a rapid disperser (ultraturax) for 2 minutes at the rate of 11,000 revolutions per minute.

 A stable emulsion was obtained, dilutable with water without loss of stability, where the size of the drops determined by optical microscopy is of the order of 6 microns.

Claims (30)

claims 1. Surfactant formed of at least one particle of nanometric dimensions based on a metal compound chosen from a phosphate or a vanadate, to the surface of which organic chains of hydrophobic nature are bonded, the bonds between said chains and the surface of said particle being distributed in a non-homogeneous manner on said surface, whereby the surface particle thus modified has an effective amphiphilic character.  2. Surfactant according to claim 1, characterized in that the particle used is an isotropic or spherical particle having an average diameter between 2 and 150 nm.  3. Surfactant according to claim 1, characterized in that the particle used is an anisotropic particle having an average diameter between 5 and 250 nm.  4. Surfactant according to any one of claims 1 to 3, characterized in that said particle is based on a metal phosphate.  5. Surfactant according to claim 4, characterized in that said particle is based on a calcium phosphate.  6. Surfactant according to claim 4, characterized in that said particle is based on a phosphate of one or more rare earth (s).  7. Surfactant according to any one of claims 1 to 6, characterized in that the organic chains of hydrophobic nature <Desc / Clms Page number 44>  linked to the surface of the particle of nanometric dimensions are alkyl chains comprising from 6 to 30 carbon atoms or polyoxyethylene-monoalkylether chains whose alkyl chain comprises from 8 to 30 carbon atoms and whose polyoxyethylene part comprises from 1 to 10 ethoxy groups -CH2-CH2-O-.  8. Surfactant according to any one of claims 1 to 7, characterized in that the connection between said organic chains and the surface of the particle is ensured by the presence, at one end of each of said chains, of a group inducing a complexing, electrostatic or hydrogen bonding type bond with a species present on the surface of the particle.  9. Surfactant according to any one of claims 1 to 7, characterized in that the modified surface of said particle is such that it can be divided by a plane of cross section into two surfaces Si and 82 such that: (i ) Each of the surfaces Si and 82 represents at least 20% of the total surface of the particle; and (ii) The surface density of organic chains linked to 82 is greater than at least 5 times the surface density of chains of hydrophobic nature linked to Si.  10. An emulsifying composition comprising at least one surfactant according to any one of claims 1 to 9.  11. An emulsifying composition suitable for producing a stabilized emulsion, of the water in oil or oil in water type, said stabilized emulsion having a content of dispersed phase greater than or equal to 20% and the average size of the drops forming the dispersed phase within said emulsion being less than or equal to 20 microns, said emulsifying composition being characterized in that it comprises particles of nanometric dimensions based on a metallic compound chosen from a phosphate or <Desc / Clms Page number 45>  a vanadate, to the surface of which are linked organic chains of hydrophobic nature.  12. An emulsifying composition according to claim 11, characterized in that it is in the form of an oil-in-water or water-in-oil type emulsion, said particles of nanometric dimensions to the surface of which the chains are linked. organic hydrophobic in nature being at least partially localized at the water / oil type interfaces of said emulsion.  13. An emulsifying composition according to claim 11, characterized in that it is in the form of a concentrated formulation having a solid content greater than 5% by mass.  14. An emulsifying composition according to claim 13, characterized in that it is formed by an ultracentrifugation pellet resulting from the ultracentrifugation of an emulsifying composition according to claim 12.  15. An emulsifying composition according to claim 11, characterized in that it is in the form of a dispersion of said particles of nanometric dimensions to the surface of which the organic chains of hydrophobic character are linked in a continuous hydrophilic or hydrophobic phase, said dispersion having a solid content of between 10 and 90% by mass.  16. An emulsifying composition according to claim 11, characterized in that it is in the form of a solid powder.  17. An emulsifying composition according to any one of claims 11 to 16, characterized in that it comprises surfactants corresponding to the definition of any one of claims 1 to 9. <Desc / Clms Page number 46>  18. A method of preparing an emulsifying composition according to any one of claims 10 to 17, characterized in that it comprises the steps consisting in: (a) forming a hydrophobic phase and an aqueous colloidal dispersion of particles of nanometric dimensions based on a metal compound chosen from a phosphate or a vanadate, said hydrophobic phase or said aqueous dispersion comprising a molecular surfactant capable of associating, by complexation, by electrostatic interaction or by hydrogen bonding, with the colloidal particles; (b) mixing by adding said hydrophobic phase to said aqueous dispersion, or by adding said aqueous dispersion in said hydrophobic phase; and (c) subjecting the mixture obtained to an emulsification.  19. The method of claim 18, characterized in that the colloidal particles of step (A) are in the form of a colloidal dispersion having a monodispersed particle size distribution, with an interparticle agglomeration rate of less than 20% by number .  20. Method according to claim 18 or according to claim 19, characterized in that the particles of step (a) consist at least partially of a calcium phosphate, a rare earth phosphate or a vanadate of rare earth.  21. Method according to any one of claims 18 to 20, characterized in that the step (c) of emulsification is followed by a step (d) of centrifugation carried out at the rate of 1000 to 5000 revolutions per minute for a period ranging from 2 minutes to 30 minutes.  22. Method according to any one of claims 18 to 21, characterized in that the emulsion obtained is further subjected to a step (e) of heat treatment, carried out by bringing the emulsion to a temperature <Desc / Clms Page number 47>  between 400C and 1000C for a period ranging from 30 minutes to 24 hours.  23. Method according to any one of claims 18 to 22, characterized in that the emulsion obtained is further subjected to a step (f) of ultracentrifugation so as to obtain a concentrated emulsifying formulation in the form of a pellet d ultracentrifugation.  24. Method according to any one of claims 18 to 23, characterized in that the emulsion obtained is further subjected to a step (g) comprising the steps consisting in: (gi) adding a solvent to the concentrated formulation, the mass of the added solvent being between 0.1 and 10 times the mass of the concentrated formulation used; and (gz) concentrating the mixture obtained by filtration or by evaporation.  25. Method according to any one of claims 18 to 24, characterized in that the emulsion obtained is further subjected to a step (f) of drying at a temperature below 150 C, whereby the emulsifying composition is obtained as a solid.  26. An emulsifying composition capable of being obtained according to a process corresponding to the definition of any one of claims 18 to 25.  27. Use of an emulsifying composition according to claim 12 for stabilizing a water-in-oil or oil-in-water emulsion, characterized in that said emulsifying composition is used at a rate of 10 to 80% by mass. relative to the total mass of the emulsion to be stabilized.  28. Use of an emulsifying composition in the form of a concentrated formulation according to claim 13 or claim 14 for stabilizing a water-in-oil or oil-in-water emulsion or a multiple emulsion, characterized in that said concentrated formulation is <Desc / Clms Page number 48>  implementation at a rate of 10 to 200% by mass relative to the mass of the dispersed phase of the emulsion to be stabilized.  29. Use of an emulsifying composition according to any one of claims 10 to 17 or according to claim 26, for the formulation of detergent compositions.  30. Use of an emulsifying composition according to any one of claims 10 to 17 or according to claim 26, for the manufacture of a packaging film.