Polystyrene latex particle surface characteristics

Abstract

Various monodisperse polystyrene latices of identical particle size, but of widely different particle surface charge density of sulphate (<0.2–1.8 μeq m −2), were prepared. The surface polarity of the polystyrene latex particle, determined from contact angle measurements of an octane drop at the latex sphere “film”/water interface, was found to increase with increasing sulphate charge density. The critical flocculation concentration of the latices increased with increasing density. The zeta potential was highly dependent on the sulphate group charge density as was the variation of the zeta potential with ionic strength. These results are indicative of a hairy particle surface layer. In addition, the plateau level adsorptions of sodium dodecyl sulphate and nonylphenol, substituted with 10 ethylene oxide units, on polystyrene latices of different charge density were determined. The adsorption data were in agreement with Vijayendran's model for the relationship between surfactant adsorption and polymer polarity (in Polymer Colloids II, R.M. Fitch (Ed.), Plenum Press, New York, 1978). Experimental evidence was obtained for the hypothesis that in the adsorption of sodium dodecyl sulphate on the various polystyrene latices not only differences in surface polarity but also electrostatic repulsions were reflected, which is contrary to the adsorption of a nonionic surfactant reflecting polarity effects only.