Adsorption of surfactants on low-charged layer silicates Part I: Adsorption of cationic surfactants

Abstract

Cationic surfactants are adsorbed in double layers on low-charged layer silicates. The amount adsorbed is determined by the swelling capacity of the layer silicates and the structure of the cationic surfactant. The swelling ability of the surfactant-layer silicate complex correlates with model concepts assuming densely packed pseudotriple layers. Higher packing densities are achieved in particular by a benzyl substituent in the surfactant. The reaction enthalpies increase in proportion to the quantity of surfactant adsorbed. This suggests that cationic surfactant adsorption takes place due to a high affinity for the interlayer surface. The differential molar reaction enthalpy is identical for the surfactants investigated, but depends on the layer silicate used. Additional heat tinting is observed in a calorimeter with increasing surfactant concentration in the interlayers of highly swelling Na hectorite. This is caused by the transition to pseudo-triple layers after double layers have been formed.