ESTIMATION OF SURFACE FREE-ENERGY OF MODI FIED PIGMENTS BY GAS-CHROMATOGRAPHY

Inverse gas chromatography was applied to study the surface properties of TiO2 used as pigments for cosmetics. The titania surfaces were mod ified by various silane coupling agents. Retention volumes for a serie s of n-alkanes and polar probes were measured using these titania as t he column packing. Retention data for nonpolar probes were shown to be dependent on the properties of modified surface; the modification was found to decrease the dispersive component of the surface free energy of the solids. Acid-base interactions were evaluated by using polar p robes according to the Lewis acid-Lewis base concepts. All pigments, i ncluding modified by silane coupling agents, had stronger interactions with the basic probe than with acidic one, demonstrating the very aci dic nature of their surfaces.