DILUTE-SOLUTION BEHAVIOR OF POLYSTYRENE LATEX-PARTICLES AND THEIR INTERACTION WITH TRITON X-100

Two samples of ''uniform'' polystyrene (PS) latex particles have been examined in detail by sedimentation and diffusion (dynamic light scattering) methods. Accurate molecular weights, particle radii, and extent of hydration were obtained. By comparison of the rates of change of sedimentation and diffusion coefficients with latex concentration, the second virial coefficient (B) was obtained and interpreted in terms of the excluded volume and charge effects. In water, it appeared that a large proportion of counterions were bound to the particle, but the addition of dilute NaCl (0.01 M) caused a considerable release of these ions. The uptake of the nonionic surfactant Triton X-100 (T) was followed by the same methods. From the decrease in diffusion coefficient, it was possible to derive the effective thickness of the adsorbed layer and an approximate adsorption isotherm. The presence of 0.01 M NaCl caused a reversal of this change in diffusion coefficient, but sedimentation measurements showed that this was not due to desorption of T but to some type of compression of the adsorbed layer. The competitive adsorption of T on the PS particles goes far to explain the removal of non-Newtonian effects when PS particles sediment through aqueous poly(ethylene oxide) solutions to which T is added.