Adsorption of aliphatic fatty acids on aquatic interfaces. Comparison between two model surfaces: the mercury electrode and δ -Al2O3 colloids

Abstract

Many organic substances in natural waters are amphipathic; i.e., they contain both a hydrophobic and a hydrophilic moiety. To assess the adsorptive behavior of such substances and to appreciate the factors that influence the distribution between particles and water, we need to understand how these substances interact with polar or nonpolar interfaces. To gain such an understanding, the adsorption of fatty acids of various chain lengths has been investigated on two model surfaces: (1) on a Hg electrode and (2) on δ-Al<SUB>2</SUB>O<SUB>3</SUB> particles. While hydrophobic expulsion dominates the adsorption on the nonpolar Hg surface, the adsorption of short-chain fatty acids (<8 carbon atoms) on the surface of hydrous Al<SUB>2</SUB>O<SUB>3</SUB> is characterized by specific coordinative interaction. Phase-selective polarography is a convenient tool to measure the extent and kinetics of adsorption of those amphipathic substances that become adsorbed primarily because of hydrophobic expulsion.