MICROEMULSIONS BASED ON THREE IMMISCIBLE LIQUIDS, COMPRISING A PERFLUOROPOLYETHER

Abstract: Microemulsions substantially consisting of : - an aqueous solution, - a perfluoropolyether having perfluoroalkyl end groups, - a hydrocarbon compound, - a fluorinated surfactant and optionally also of a hydrogenated or fluorinated alcohol, said microemulsions being in the form of a limpid or opalescent liquid, macroscopically consisting of a single phase, stable in a certain temperature range. The dispersing phase (or continuous phase) in the microemulsion may consist of one of the three abovesaid liquid components, wherefore the microemulsion may be of the oil-in-water or water-in-oil type.

Description: The term "microemulsion", whenever used in the scientific literature, means a system macroscopically consisting of a single limpid or slightly opalescent liquid phase, comprising two immiscible liquids, and characterized by the following properties: it is optically transparent or opalescent, it forms spontaneously by simple mixing of the components, independently of the order of mixing, it exhibits thermodynamic stability: it is indefinitely stable in a certain temperature range, it exhibits demixing reversibility: temperatures not within the range of existence cause separation into two or more than two phases, but the microemulsion spontaneously forms again as soon as the temperature is brought again within the range of existence. The microscopic structure of the microemulsions reveals the presence of liquid dispersed particles having sizes in the range from 5 to 200 nm (50 to 2000 Å). Also different system structures are possible, such as a mutual interdispersion of the two liquids in the form of tridimensional films, or a "co-solubilization", in which the fluids are interdispersed as regards their molecules. Essential condition for obtaining a microemulsion is that the interface tension between the immiscible component liquids be reduced to a very low value owing to the presence of suitable amounts of proper surfactants. "Oil-in-water" (o/w) microemulsions are known in which the dispersed phase is a fluorinated compound with partially hydrogenated molecule (US-A-3,778,381) and the o/w and w/o ("water-in-oil") microemulsions based on perfluoropolyethers are described in EP-A-250 766, a document relevant under Art. 54(3) EPC. DE-A-23 19 971 describes a "normal" emulsion of a fluorinated organic compound of more than 4 carbon atoms which is dispersed in an aqueous system. Since the dispersed droplets have a size in the micron (µm) range the resulting emulsion is termed "microemulsion". JP-A-60-34730 discloses that a perfluoropolyether emulsion prepared from certain perfluoropolyethers, non-ionic surfactant, hydrophilic organic solvent and H₂O is stable and useful for fiber treatment. Known in literature are multiple emulsions of the common type, consisting of more than two immiscible phases; for example in a o/w/o system, the water phase separates the two reciprocally immiscible oil phases. Known too are emulsions of the common type, consisting of three phases, comprising perfluoropolyethers, described in IT-A-20161 A/85 (Monteflous S.p.A). Conversely, microemulsions in which the dispersed phase consists of two liquids immiscible with each other and immiscible with the dispersing liquid phase are not known so far. It has surprisingly been found that it is possible to prepare microemulsions which comprise three mutually immiscible liquids consisting of : an aqueous solution, a perfluoropolyether having perfluoroalkyl end groups (as defined hereinbelow), a non - fluorinated hydrocarbon compound (as defined hereinbelow), and furthermore: a fluorinated surfactant, and optionally co-surfactants belonging to the class of the hydrogenated (i.e. non-fluorinated) and/or fluorinated alcohols, non-fluorinated surfactants. Also electrolytes may be present in some cases. The microemulsions are preparable simply by mixing the individual components in any order, or by mixing the binary microemulsions, formed by couples of the abovesaid starting liquids. The fluorinated surfactants contained in the microemulsions according to the present invention may be ionic or non-ionic. In particular there can be cited: a) the perfluorocarboxylic acids with 5 to 11 carbon atoms and the salts thereof; b) the perfluorosulphonic acids with 5 to 11 carbon atoms and the salts thereof; c) the non-ionic surfactants indicated in EP-A-51526 (US-A-4,451,954); d) the mono- and di-carboxylic acids derived from perfluoropolyethers and the salts thereof; e) the non-ionic surfactants consisting of a perfluoropolyether chain linked to a polyoxyalkylene chain; f) the perfluorinated cationic surfactants or those deriving from perfluoropolyethers having 1, 2 or 3 hydrophobic chains. Furthermore, the system may contain hydrogenated non-ionic, anionic or cationic surfactants and co-surfactants. The surfactants and co-surfactants which are preferred in the present invention comprise all the surfactants and co-surfactants which are utilized for preparing microemulsions of hydrocarbons. (Examples of surfactants and of co-surfactants can be found in "Macro- and Micro-emulsions" D.O. Shah., Ed., ACS Symposium series 272, ACS, Washington 1985). As already mentioned hereinbefore, the microemulsions of the present invention are macroscopically composed of a single limpid or translucid phase, which is stable within a certain temperature range which depends on the perfluoropolyether concentration and on its molecular weight, on the type and concentrations of the surfactant, on the presence, if any, of alcohols, salts and acids. Utilizable surfactants are for example: hydrogenated alcohols with 1 to 12 carbon atoms, alcohols derived from perfluoropolyethers, alcohols comprising a perfluoropolyether chain, (partially) fluorinated alcohols. The perfluoropolyethers for the formation of the microemulsions of the present invention are those having an average molecular weight from 500 to 10,000 and preferably from 600 to 3000, and belonging to one or more of the following classes : 1) with a random distribution of the perfluorooxyalkylene units, wherein R f and R' f , equal or different from each other, are -CF₃, -C₂F₅ or -C₃F₇, and m, n, p have such average values as to fulfil the abovesaid conditions as regards the average molecular weight. 2) R f O(CF₂CF₂O) n (CF₂O) m R′ f with a random distribution of the perfluorooxyalkylene units, wherein R f and R′ f , either like or unlike each other, are -CF₃ or -C₂F₅, and m and n have such average values as to fulfil the abovesaid conditions. 3) with a random distribution of the perfluorooxyalkylene units, wherein R f and R′ f , like or unlike each other, are -CF₃, -C₂F₅ or -C₃F₇, and m, n, p, q have such average values as to fulfil the abovesaid conditions. 4) wherein R f and R′ f , like or unlike each other, are -C₂F₅ or C₃F₇ and n has such value as to fulfil the abovesaid conditions. 5) R f O(CF₂CF₂O) n R′ f , wherein R f and R′ f , like or different from each other, are -CF₃ or C₂F₅, and n has such an average value as to fulfil the above-cited conditions. 6) R f O(CF₂CF₂CF₂O) n R′ f , wherein R f and R′ f , equal to or different from each other, are -CF₃, -C₂F₅ or -C₃F₇, n having such an average value as to fulfil the abovesaid conditions. Perfluoropolyethers of class 1) are known in commerce under the trademark Fomblin® Y or Galden®, the ones of class 2) are known under the trademark Fomblin® Z, all of them being produced by Montedison S.p.A. Commercially known products of class 4) are the Krytox® (Du Pont) perfluoropolyethers. Those of class 5) are described in US-A-4,523,039. Those of class 6) are described in EP-A-148,482 (Daikin). The ones of class 3) are prepared according to US-A-3,665,041. Other suitable perfluoropolyethers are the ones described by Lagow et al. in US-A-4,523,039 or in J. Am. Chem. Soc. 1985, 107, 1197-1201. The hydrocarbon compounds (oils) present in the microemulsions of the present invention are compounds which are liquid at the microemulsion stability temperature and belong to the classes of straight, branched and cyclic aliphatic hydrocarbons, aryl and heterocyclic hydrocarbons and the functional derivatives thereof, such as esters and amides, having a number of carbon atoms ranging from 1 to 50 and preferably from 5 to 20. In the preparation of microemulsions according to the present invention, systems were obtained in which the aqueous phase and the hydrocarbon phase are microdispersed in the perfluoropolyether matrix, and systems in which the perfluoropolyether and the hydrocarbon phase are microdispersed in the aqueous phase, as well as systems in which the aqueous phase and the perfluoropolyether phase are microdispersed in the hydrocarbon phase. There is no intention of making assumption herein about the structure of the three-phase system, and in particular about the position of the hydrocarbon phase. This could be present, for example, in the form of separated droplets, or it could be present inside the surfactant's interphase film, or it could be preferably solubilized inside a single phase (water or perfluoropolyether) or in two or more possible different positions. At present, the conditions leading to the formation of multiple microemulsions cannot be foreseen "a priori" and strongly depend on the chemico-physical characteristics of the liquids and of the surfactants which have been utilized. The microemulsions of the present invention are utilizable as systems endowed with detergent and protective properties connected with the simultaneous presence of surfactants, hydrocarbon oils and perfluoropolyethers. The microemulsions of the present invention can be used in particular in preparing lubricants containing water-soluble additives, in order to confer high stability of the additive dispersion in the oil. Another interesting use of the microemulsions of the present invention consists in using the same as additive in fluorinated monomers polymerisation processes as disclosed in CA-A-1,180,603: in fact the perfluoropolyether microemulsions of the present invention afford the same function as the perfluoropolyether additives in form of conventional emulsions of the above cited prior art. The following examples are given merely to illustrate possible embodiments of the invention. Example 1 Prepared was a solution containing 11 ml of an acid having a perfluoropolyether structure belonging to class 1) with R' f = -CF₂COOH and having an average equivalent weight of 690, 10 ml of a NH₃ solution at 10% by weight, 6 ml of absolute ethanol and 20 ml of bidistilled water. To this solution, 6 ml of a perfluoropolyether oil belonging to class 1), having an average molecular weight of 800 were added. The system consisted of a single limpid phase, stable at room temperature and capable of solubilizing 2 ml of cyclohexane. A limpid, macroscopically monophase liquid, stable between 15°C and at least 70°C was obtained. If S designates the fluorinated surfactant utilized, CoS the co-surfactant (ethanol), w the water, O f the perfluoropolyether oil, O h the hydrocarbon (cyclohexane), the microemulsion composition expressed in % by weight was as follows : S + CoS = 38.4 % w = 43.4 % O f = 15.9 % O h = 2.3 %. Example 2 The system described in example 1 and in the same amounts as therein indicated solubilized 1 ml of benzene, providing a limpid phase stable from 10°C to 57°C. The wt.% of the components were as follows : S + CoS = 37.9 % w = 44.4 % O f = 16.2 % O h = 1.3 %. Example 3 The microemulsion of perfluoropolyether in water described in example 1, utilized in the same amounts, was capable of solubilizing 2 ml of n-pentane; by feeding the surfactant amount, it was possible to raise the amount of solubilized hydrocarbon. Microemulsions containing up to 4.7% by weight of n-pentane were stable at room temperature. Obtained were microemulsions having the following compositions : S + CoS = 31.3 % w = 43.1 % O f = 15.8 % n-C₅H₁₂ = 2.7 % S + CoS = 57.2 % w = 21.0 % O f = 17.1 % n-C₅H₁₂ = 4.7 %. Example 4 In the microemulsion described in example 1, taken in the same amount, it was possible to solubilize 2 ml of n-hexane, thereby slowly obtaining a new limpid phase, stable at room temperature. The microemulsion exhibited the following composition : S + CoS = 35.1 % w = 46.0 % O f = 16.9 % O h = 2.0 %. Example 5 The preceding examples described microemulsions in which the continuous phase was the aqueous phase, but also microemulsions in which the dispersant was the perfluoropolyether phase were obtained. In particular, 10 ml of a carboxylic acid with perfluoropolyether structure, having an average equivalent weight of 636, salified with 5 ml of an ammonia solution at 10% by weight, in the presence of 16 ml of perfluoropolyether belonging to class 1), with an average molecular weight equal to 800, and of 4 ml of n-pentane, dissolved 3 ml of water. A room temperature-stable microemulsion having the following composition was obtained : S = 31.2 % w = 13.8 % O f = 50.7 % O h = 4.3 %. Example 6 A system composed by 25 ml of perfluoropolyether of class 1), having an average molecular weight of 800, and by 4 ml of n-hexane dissolved 2 ml of water, in the presence of 11.544 g of ammonium salt of a carboxylic acid having perfluoropolyether structure, having an average molecular weight equal to 634, of 1 ml of the same acid and of 1 ml of t-butanol as a co-surfactant. Obtained was a limpid phase, stable to room temperature, having the following composition : S + CoS = 21.9 % w = 3.1 % O f = 70.9 % O h = 4.1 %. The following examples illustrate the method of preparing microemulsions according to the invention, obtained by mixing binary microemulsions, for example a microemulsion of perfluoropolyether in water plus a microemulsion of a hydrocarbon in water. Example 7 Prepared was a limpid microemulsion of toluene in water, stable at room temperature and having the following composition in % by weight : sodium dodecylsulphate (SDS) 4.8% water 88.9% C₅H₁₁OH 6.7% toluene 4.6%. Prepared was also a microemulsion of perfluoropolyether - having an average molecular weight of 650 - in water, in the presence of a carboxylic acid having a perfluoropolyether structure and an average molecular weight of 367, salified with an ammonia solution at 10% by weight of NH₃. The solubilized system was stable at room temperature and contained : By mixing 5.3 ml of PFPE/water microemulsion and 3 ml of toluene/water microemulsion it was possible to obtain a limpid system, indefinitely stable at a temperature lower than 24°C, in which PFPE (9.4%) and toluene (1.5%) were simultaneously solubilized in water (64.2%), in the presence of a mixture of hydrogenated and fluorinated surfactant (22.9%) and of amyl alcohol (2.0%). Example 8 A fluorinated microemulsion was prepared by mixing 1 ml of PFPE having an average molecular weight equal to 660, 1 ml of an aqueous ammonia solution at 10% by weight, 1 ml of a surfactant having a perfluoropolyether structure with a -COOH end group and an average molecular weight equal to 634, and 0.1 ml of a 0.1 M KNO₃ solution. The system was limpid and indefinitely stable at room temperature. By adding to the microemulsion so prepared 0.5 ml of the toluene/water microemulsion described in example 7, an isotropic, limpid system, stable at temperatures lower than 22°C, was obtained, in which water (29.7%) and toluene (0.4%) were solubilized in PFPE (33.8%) in the presence of ionic, hydrogenated and fluorinated surfactants and of a hydrogenated co-surfactant. Example 9 A system containing 5 ml of PFPE having an average molecular weight equal to 650, 22.2 ml of an acid with PFPE structure and an equivalent weight of 636, and 1 ml of an ammonia solution at 10% by weight, solubilized 0.7 ml of the toluene-in-water microemulsion described in example 8. The system obtained was limpid at room temperature and retained its characteristics also when subjected to heating up to 62-68°C. In this case, 10.8% of the water phase, consisting of a microemulsion of toluene in water, was solubilized in PFPE (61.4%). The toluene amount present in the system was equal to 0.2% by weight. Example 10 A water-in-toluene microemulsion, stable at room temperature, having the following composition : was prepared. Prepared was also a solution containing 1.750 g of ammonium salt of the carboxylic acid having a perfluoropolyether structure and having an average equivalent weight equal to 694, 5 ml of PFPE having an average molecular weight equal to 650 and 1 ml of an alcohol having structure H(CF₂)₆CH₂OH; this system was limpid at room temperature and solubilized 0.5 ml of the above-described w/OH microemulsion. The resulting system was limpid up to above 60°C and exhibited the following composition : Example 11 Prepared was a system comprising 1 ml of an acid with PFPE structure having an average equivalent weight of 367, 0.5 ml of an ammonia solution at 10% by weight of NH₃, 0.0351 g of sodium dodecylsulphate, 1.5 ml of n-butanol, 5 ml of toluene and 0.6 ml of fluorinated alcohol H(CF₂)₆ CH₂OH; this system consisted only of one limpid phase, which was anisotropic at temperatures higher than 40°C. Such system was capable of solubilizing 0.1 ml of PFPE having an average molecular weight equal to 650. The resulting solubilized system had the following composition : and was stable, as a limpid single phase, at temperatures higher than 44°C. Example 12 2.9725 g of a water-in-toluene microemulsion, stable at room temperature and containing : were capable of solubilizing 0.2 ml of PFPE having an average molecular weight equal to 600, so providing a limpid system, stable at temperatures higher than 36°C, having the following composition : SDS 0.27 % n-BuOH 16.40 % toluene 58.40 % PFPE acid, 367 11.20 % Water 3.31 % PFPE 10.42 %. Example 13 It is possible to obtain solubilized systems of three immiscible phases also by using non-ionic surfactants. In particular, a w/OF/OH microemulsion was prepared by adding to 2.6254 g of Triton® X100 dissolved in 5 ml of toluene, 0.2 ml of a perfluoropolyether having an average molecular weight equal to 600 and 0.9 ml of an acid having a perfluoropolyether structure and an average equivalent weight equal to 367, partially salified with 0.2 ml of a solution at 10% by weight of NH₃, in the presence of 1.6 ml of an alcohol having structure H(CF₂)₆CH₂OH. Obtained was a system consisting of a limpid single phase, stable from room temperature up to above 70°C, having the following composition : It should be noticed that the sane amount of PFPE is not soluble in the Triton® X100/toluene system in the absence of a surfactant with perfluoropolyether structure and of a co-surfactant. Example 14 A microemulsion of PFPE in water was prepared by mixing 10 ml of carboxylic acid derived from PFPE having an average equivalent weight of 694, 10 ml of an ammonia solution at 10% by weight, 20 ml of water, 6 ml of ethanol and 6 ml of PFPE having an average molecular weight of 800. The microemulsion was stable at temperatures lower than 30-35°C and it was alkaline (pH = about 10) due to the excess of base utilized to salify the surfactant. 5.2 ml of this microemulsion were brought to a pH = 7 by addition of 0.75 ml of carboxylic acid having a perfluoropolyether structure and an average equivalent weight of 634. The OF/w microemulsion so obtained was stable at temperatures higher than 43°C and was capable of solubilizing 0.6 ml of butyl acetate, thereby forming a system, which was limpid and isotropic at temperatures higher than 45°C. At room temperature, the system was cloudy, highly viscous and strongly birefractive. The resulting microemulsion was composed of 11.8% by weight of ester and of 88.2% of fluorinated microemulsion. Actually, the ester constitutes a third immiscible phase as it is insoluble both in PFPE and in the water/alcohol mixture of this example. Example 15 0.6 ml of CH₃COOC₄H₉ were not miscible with 3 ml of water and 0.6 ml of ethanol in the absence of the surfactant: however it was possible to obtain the solubilization of the ester by addition of 1.7983 g of ammonium salt of the carboxylic acid having a perfluoropolyether structure and an average equivalent weight equal to 694. The system so obtained consisted of a phase, which was limpid at temperatures higher than 58°C, while at temperatures lower than 58°C is was birefractive and highly viscous. This system was capable of solubilizing 0.2 ml of PFPE having an average molecular weight equal to 800, thereby forming a microemulsion, which was stable at a temperature higher than about 40°C and exhibited the following composition:

Claims: A microemulsion in the form of a limpid or opalescent liquid, macroscopically consisting of a single phase, stable in a defined temperature range, prepared by starting from three mutually immiscible liquids and characterized in that it comprises: (i) an aqueous solution, (ii) a perfluoropolyether having perfluoroalkyl end groups, (iii) a non-fluorinated hydrocarbon compound, and, furthermore, (iv) a fluorinated surfactant optionally combined with (v) a co-surfactant; said perfluoropolyether (ii) having an average molecular weight of from 500 to 10,000 and being selected from the following classes: a) with a random distribution of the perfluorooxyalkylene units, wherein R f and R' f , equal to or different from each other, are -CF₃, -C₂F₅ or -C₃F₇, and m, n, p have such average values as to fulfil the abovesaid conditions concerning the average molecular weight; b) R f O(CF₂CF₂O) n (CF₂O) m R' f with a random distribution of the perfluorooxyalkylene units, wherein R f and R' f , like or different from each other, are -CF₃ or -C₂F₅, and m and n have such average values as to fulfil the abovesaid conditions; c) with a random distribution of the perfluorooxyalkylene units, where R f and R' f , like or different from each other, are -CF₃, -C₂F₅ or -C₃F₇, and m, n, p, q have such average values as to fulfil the abovesaid conditions; d) where R f or R' f , like or different from each other, are -C₂F₅ or -C₃F₇, and n has such a value as to fulfil the abovesaid conditions; e) R f O(CF₂CF₂O) n R' f , where R f and R' f, like or different from each other, are -CF₃ or -C₂F₅, and n has such an average value as to fulfil the abovesaid conditions; f) R f O(CF₂CF₂O) n R' f , where R f and R' f , like or different from each other, are -CF₃, -C₂F₅ or -C₃F₇, n having such an average value as to fulfil the abovesaid conditions; and said non-fluorinated hydrocarbon compound (iii) being a product which is liquid at the microemulsion stability temperature and being selected from straight, branched and cyclic alkyl hydrocarbons and aryl and heterocyclic hydrocarbons and functional derivatives thereof, having a number of carbon atoms ranging from 1 to 50. The microemulsion according to claim 1, wherein the fluorinated surfactant (iv) is selected from the following classes: a) perfluorocarboxylic acids with 5 to 11 carbon atoms and their salts; b) perfluorosulphonic acids with 5 to 11 carbon atoms and their salts; c) non-ionic surfactants, as are indicated in EP-A-51526; d) mono- and di-carboxylic acids derived from perfluoropolyethers and their salts; e) non-ionic surfactants consisting of a perfluoropolyether chain linked to a polyoxyalkylene chain; f) perfluorinated cationic surfactants or those derived from perfluoropolyethers having 1, 2 or 3 hydrophobic chains. The microemulsion according to any one of claims 1 and 2, wherein co-surfactants (v) selected from: alcohols having a perfluoropolyether chain, hydrogenated alcohols with 1 to 12 carbon atoms, fluorinated alcohols are present. The microemulsion according to any one of claims 1 to 3, wherein non-fluorinated surfactants of the ionic and non-ionic type are present. A process for preparing the microemulsion according to claim 1, consisting in mixing the components, in any order. A process for preparing the microemulsion according to claim 1, consisting in mixing two binary microemulsions based on the above-indicated components. Use of the microemulsion according to claim 1 in the preparation of lubricants containing water-soluble additives.

Inventors: CHITTOFRATI, ALBA, VISCA, MARIO
Applicants: AUSIMONT S.P.A.
Application year: 1988
Main classification: C08J3
IPC codes: B01F17, C11D17, C07C41, C07C43, C11D1, C07C67, C08J3, B01J13, C10M173