Oil-in-water photoprotective emulsions containing gemini surfactants and associative polymers

A photoprotective composition for protecting the skin and/or the hair against UV radiation, comprising:

• as liquid phase, an oil-in-water emulsion, emulsified with at least one dimeric surfactant comprising two surfactant units, which are identical or different, each comprising a hydrophilic head and a hydrophobic tail and connected to each other, via the hydrophilic heads, by means of a spacer group, said dimeric surfactant being an anionic dimeric surfactant of formula (I):
• in which
• R1 and R3 each represent a linear or branched C5-C25 alkyl group, which is saturated or having up to two non-vicinal unsaturations,
• R2 represents a C1-12 alkylene group,
• X and Y each represent a group (C2H4O)x(C3H6O)y—RF with x=0-15, y=0-10, x+y≧1, and RF═—SO3M, —CH2—CO2M, —P(O)(OM)2, H, —C3H6SO3M or a —CH2(CHOH)4CH2OH group when x+y=0, and
• M represents an alkali metal ion, (alkyl)ammonium, alkanolammonium, H or a ½ alkaline-earth metal ion, the concentration of the dimeric surfactant(s) being between 0.01% and 4% by weight relative to the total weight of the photoprotective composition,
• a photoprotective system which screens out UV rays, comprising at least one mineral nanopigment based on metal oxide, and
• at least one associative polymer comprising at least one C8-40 fatty chain, which is an anionic, cationic or amphoteric polymer or a non-ionic polymer selected from the group consisting of hydroxypropyl guars modified with groups comprising at least one fatty chain, copolymers of vinylpyrrolidone and of fatty-chain hydrophobic monomers, copolymers of C1-C6 alkyl methacrylates or acrylates and of amphiphilic monomers comprising at least one fatty chain, copolymers of hydrophilic methacrylates or acrylates and of hydrophobic monomers comprising at least one fatty chain, and copolymers of PEG-180, of tetramethoxymethylglycouril and of laureth-50 or octoxynol-40,
• the concentration of the associative polymer(s) being between 0.01% and 10% by weight relative to the total weight of the photoprotective composition.