Nanostructured Surface Treatment Enables the Combination of Nano-particulate ZnO and Acrylate-based Polymers In Cosmetic Formulations

Keywords:
ZnO, suncare, acrylate polymers

Abstract:
Modern skin care formulations must meet high standards of efficacy, skin compatibility and aesthetic appeal. It is commonly accepted that the performance of a cosmetic product is related to the entire formulation and an optimal galenic formulation that incorporates active ingredients is a necessary prerequisite to succeed in the market. ZnO is an active ingredient in OTC suncare product. However problems are encountered when particulate zinc oxide, particularly nano-particulate zinc oxide, is formulated with charged organic moieties, such as acrylate-based polymers, á- and â-hydroxy acids, etc. Contemporary skin care formulations are emulsions. The charged organic moieties will reside in the aqueous phase of the emulsion and the inorganic ingredients, such as zinc oxide, reside in the oil phase of the dispersion. In formulation the acrylate-based polymers, once neutralized, chain extend to thicken the formulation by increasing the viscosity of the aqueous phase. Other charged organic moieties, such as á- and â-hydroxy acids, may have other functions such as enhancing epithelial cell regeneration. However zinc ions from the particulate zinc oxide migrate from the oil phase to the aqueous phase and adversely interact with the charged organic moieties to either cause collapse of the acrylate-based polymers or the formation of organic salts with concomitant dissolution of the particulate inorganic. A new nanostructured surface treatment that passivates ZnO and enables it to be used in formulations containing charged organic moieties will be reported. The surface treatment is comprised of a star-graft siloxane copolymer containing looped structures. Typically nano-particulate surfaces treated with a siloxane star-graft copolymers (US Patents 5, 993, 967 and 6, 033, 781) enable compatibility without particulate aggregation, but are subject to the limitations enumerated above. The presence of the loop structure in the surface treatment enables the formulation of elegant skincare products. The nano-structured surface treatment will be described, formulation guidance given, and formulation efficacy will be compared with state-of-the-art products.

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Nanotech 2005 Conference Program Abstract