ADSORPTION OF SODIUM DODECYL-SULFATE ON POLYSTYRENE LATEX-PARTICLES USING DYNAMIC LIGHT-SCATTERING AND ZETA-POTENTIAL MEASUREMENTS

The adsorption of sodium dodecyl sulfate (SDS) to polystyrene latex pa rticles of low negative charge has been examined as a function of surf actant concentration by estimation of the hydrodynamic radius and also the zeta potential (zeta) by electrophoretic measurements. Adsorption isotherms were also determined by a surface tension method. Adsorptio n at zero and low ionic strength (10(-3) M) is two-stepped: an initial hydrophobically-driven adsorption of single surfactant molecules foll owed at increased SDS concentrations by a cooperative adsorption at SD S concentration close to the critical micelle concentration (cmc). At higher ionic strength (0.032 M), the initial adsorption is succeeded b y two maxima in R(H) and zeta, where the second step may be related to further growth of the primarily adsorbed SDS micelles. The influence of temperature on the adsorption is small but significant.