THE DIELECTRIC RESPONSE OF POLYSTYRENE LATEXES - EFFECTS OF ALTERATIONS IN THE STRUCTURE OF THE PARTICLE SURFACE

The presence of a "hairy" layer has been hypothesized to explain discrepancies between the electrokinetic theory and experiments with polystyrene latexes by Van der Put and Bijsterbosch (J. Colloid Interface Sci.92, 499 (1983)]. We tested the hypothesis by making electrokinetic measurements on latexes before and after they had been heated above the polystyrene glass transition temperature. This sort of treatment may smooth the particle surface by collapsing or removing the charged polymer filaments which comprise the layer. Low-frequency dielectric measurements reveal that heat treatment improves the agreement between experiment and theory. For an amphoteric latex, the dielectric constant and conductivity decrease with heat-treatment time, and the characteristic relaxation frequency increases. This is consistent with the hairy surface hypothesis, suggesting that heat treatment smooths the surface, creating particles which more closely conform to the assumptions of the classical theory. Experiments with an anionic latex further suggest the presence of surface structure, but discrepancies between experiment and theory persist; it appears that factors other than hairiness contribute to these discrepancies. The suspension's dielectric properties are evidently very sensitive to the state of the particle surface, and thus dielectric spectroscopy offers a promising means of studying the structure of colloidal interfaces. © 1990.