COAGULATING ACTION OF A CATIONIC SURFACTANT AND ELECTROLYTE IN AQUEOUS DISPERSIONS OF HYDROPHILIC SILICA.

A study has been made of the effect of cetyl pyridinium bromide (CPB) on the stability of colloidal dispersions of hydrophilic (unmodified) Aerosil in water both in the absence of added electrolyte and in the presence of 10** minus **1 M NaCl; also studied was the adsorption of CPB onto the dispersed particles. In the absence of CPB, the dispersions are stable both in pure water and in the 10** minus **1 M NaC1 solution. In the presence of the 10** minus **1 NaC1, however, coagulation begins at lower CPB concentrations. No substantial effect of the NaC1 on the adsorption of CPB was detected. The results indicate that coagulation is due not only to the suppression of the electrostatic repulsion between the ions, but also to a hydrophobic interaction that arises on the adsorption of the cationic surfactant.