Electrokinetic study of polymer surfaces

Abstract

On the basis of electrokinetic measurements in thin quartz capillaries coated with micrometer-thick polystyrene (PS) layers, values of ζ-potentials and of surface charge σ in different electrolyte solutions were calculated. Potentials of adsorption of K +, Ba 2+, La 3+, and Cl - ions on a hydrophobic PS surface were computed with equations of localized adsorption. For hydrophilic copolymers of PS with polyacrylic acid (PA) the mechanism of charge formation is connected with dissociation of COOH groups. For 4% of PA in copolymer, the surface charge increases to 4 μC/cm 2 at pH 11, which is 10-fold as compared with PS. A further increase in PA content (up to 40%) causes the formation of charged surface “brush” layers. Dissociation of COOH groups within a brush layer leads to very high values of surface charge (up to −160 μC/cm 2) and surface conductivity. The relative value of surface conductivity decreases from κ s κ v = 3.2 to 1 when the concentration of KC1 solution increases from 10 −4 to 10 −1 N.