Electrokinetic Potential of Spherical Glass Particles covered with Dodecyl Amine

Abstract

ξ-Potential of spherical glass particles measured by streaming potential method showed a negative value, and had minimum in 1 mM NaCl concentration. In higher concentration, ξ-value decreased gradually because of the effect of ionic strength. ξ-Potential of glass particles in NaCl solution showed a higher value when the solution contained dodecyl-amine than in its absence, but the value was negative even in saturated solution of dodecylamine. It was confirmed microscopically that the glass particles were smoothly coated with dodecylamine by fusion-dispersion-cooling method and that these were stable in NaCl solution for several hours. As the amount of dodecylamine coating on glass particles increased, ξ-potential increased and reached zero with the thickness of the amine layer of 100-150 Å, and had a maximum point at 400 -500 Å thickness and showed a constant value was found, after gradual decrease with the increasing thickness of the dodecylamine layer. Almost the same value as the maximum value was obtained by electrophoresis method, and, therefore, these particles were regarded to be very densely covered with dodecylamine. The charge density of the surface, σ, and the amount of excessive adsorption of ions to bare glass surface, (△σ/F), were calculated from the Gouy-Chapman equation. With the increasing amount of the coated dodecylamine, σ of coated particles increased to possitive values, in NaCl solution of constant concentration. When the amount of dodecylamine coated on the glass was more than 7 mg/g, σ showed a constant value because only the dodecylamine near the surface of the coated particles was capable of dissociating electrically.