ELECTROKINETIC AND ADSORPTION PROPERTIES OF SIO2 IN POLYMER AND SURFACTANT SOLUTIONS

A combined investigation of the electrokinetic and adsorption properties of SiO2 in solutions of weak polyelectrolytes (poly(ethylenimine), PEI, and poly(acrylic acid), PAA) and of an uncharged surfactant (C8H15CeH4O(C2H4O)mH, OP-7) was carried out. Electrokinetic measurements were performed on a plane-parallel fused quartz capillary, and adsorption measurements were carried out on Aerosil with a specific surface area of 175 m2 g-1. When OP-7 is adsorbed on SiO2, the surface charge and specific surface conductivity at neutral pH practically do not change. The detected decrease in the absolute value of the zeta potential in OP-7 solutions is caused by the displacement of the slipping plane into the bulk of the solution. In polyelectrolyte solutions containing polyanions, slight adsorption leads to a definite increase in the zeta potential and the surface conductivity. Specific interactions between the polycation and the SiO2 surface is manifested in the negative surface charge increase, the displacement of the isoelectric point, the change of the sign of zeta and a decrease in the surface conductance. We show the competing adsorption of uncharged surfactant molecules and polyions in mixtures of polyelectrolyte and a surfactant.