Critical phenomena in aqueous solutions of long-chain quaternary ammonium salts

Abstract

Solutions of hyamine 1622 (di-isobutyl phenoxy ethoxy ethyl dimethyl benzyl ammonium chloride) at concentrations above the critical micelle concentration have been studied as a function of NaCl concentration and temperature. At a given temperature there is a critical NaCl concentration above which the system separates into two layers; the top layer is practically free of the quaternary ammonium salt and the bottom layer shows the characteristics of an oil. The volume of the bottom layer decreases with increasing NaCl concentration. Before the onset of the two-phase separation, the turbidity and the dissymmetry of light scattering increases with increasing NaCl concentration. Small temperature changes produce a marked change in the stability of the bottom layer. In the immediate neighborhood of the critical temperature the system exhibits a marked opalescence. The experimental results can be explained in terms of current concepts of critical solution phenomena where NaCl alters the interactions between the micelles of the quaternary ammonium salt. The details of the interactions are given qualitatively by the theory of Verwey and Overbeek.