Estimation of Surface Free Energy of Modified Pigments by Gas Chromatography

Abstract

Inverse gas chromatography was applied to study the surface properties of TiO₂ used as pigments for cosmetics. The titania surfaces were modified by various silane coupling agents. Retention volumes for a series of n-alkanes and polar probes were measured using these titania as the 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 probes according to the Lewis acid-Lewis base concepts. All pigments, including modified by silane coupling agents, had stronger interactions with the basic probe than with acidic one, demonstrating the very acidic nature of their surfaces.