Effect of the surface-active substance cetylpyridinium chloride on the electric light scattering of bentonite

Abstract

The changes in the electric properties and the stability of an aqueous suspension of sodium bentonite on addition of the cationic surface-active substance cetylpyridinium chloride (CPC) is studied by electric light scattering. The CPC concentration varies from 10 −5 to 10 −3 mol l −1, and the suspension weight concentration is 5 · 10 −6 kg l −1. The dimensions of the bentonite particles are followed by electron microscopy and the decay of the electro-optic effect. The particle dimensions are greatest at the isoelectric point (10 −4 mol l −1 CPC), determined microelectrophoretically. The greater value of the electro-optic effect in the kHz range for suspensions to which CPC is added in comparison with untreated suspensions is explained by the increase of the particle dimensions, which leads to an increase in the particle electric polarizability. The electric polarizability per unit interfacial area of the particles decreases, which is related to CPC adsorption on the particles. The greater dispersion for suspensions with CPC at frequencies below 100 Hz, also manifest in large negative effects, is explained by the increase of the ratio of permanent dipole moment to induced dipole moment.