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J. Cosmet. Sci., 60, 617–625 (November/December 2009) 617 The effect of cationic polymer treatment on adhesion of iron oxide to eyelashes S. KO, Y. H. ROH, J. H. CHOO, S. H. JANG, S. H. HAN, and H. G. JANG, Korea University, Seoul 136-701 (S.K., H.G.J), and AMOREPACIFIC R&D Center, Yongin 446-729 (S.K., Y.H.R., J.H.C., S.H.J., S.H.H.), Republic of Korea. Accepted for publication June 15, 2009. Synopsis The aim of this study was to investigate the effect of iron oxide application on improving the volume of eyelashes. Iron oxide, having a negative surface charge in its natural form, was coated with commercial cat- ionic polymers to increase its adhesion. The iron oxides coated with different types and concentrations of these polymers were incorporated into a basic mascara formula to test their volume effects by means of the weight difference of eyelashes. The results indicated that the type and concentration of coating materials affect the surface zeta potential and particle cluster size of iron oxides. The type of cationic polymer, especially, was shown to modify both factors of iron oxide. The obtained results also suggested that the volume effect of mascara increases with a higher positive surface zeta potential and a smaller particle cluster size of the coated iron oxides. INTRODUCTION Iron oxides are a class of coloring matter used in cosmetics for application on skin or keratin fi bers. In the past few decades, they have become an increasingly important com- ponent of color cosmetics, especially as a primary ingredient in eye makeup. Much research on iron oxides, in surface treatment, material hybridization, and morphology control, has been conducted to improve the long-lasting effect, skin adhesiveness, and smooth texture of the fi nal cosmetic product (1). Pigments treated with methicone, dimethicone, or alkyl silane are known to present waterproof effects due to the hydrophobicity of these silicone materials. Perfl uoro compounds, especially polytetrafl uoroethylene (PTFE), have a lower surface energy than any oil, thus granting stronger long-lasting effects against hydrophobic solvents. Skin adhesion can be improved by coating pigments with keratin or silanyl glutamate. Keratin, being the basic component of skin, demonstrates higher affi nity, and silanyl Address all correspondence to H. G. Jang.