The Configuration of Sodium Poly(styrene sulfonate) at Polystyrene/Solution Interfaces 1 T. COSGROVE, T. M. OBEY, AND B. VINCENT School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1 TS, United Kingdom Received December 3, 1985; accepted December 5, 1985 Adsorption isotherms, adsorbed layer hydrodynamic thicknesses(from photon correlation spectroscopy), and segment density profiles (from small angle neutron scattering) have been determined as a function of ionic strength for two, narrow-molecular-weight samples of sodium poly(styrene sulfonate) on poly- styrene latex particles. Four latices were used, one having a high negative surface charge and three of varying positive surface charge density. The adsorbed amounts are strongly dependent on ionic strength, but not strongly dependent on the polyelectrolyte molecular weight. With increasing surface charge on the positive latex particles, the adsorbed amount decreases. The hydrodynamic thicknesses are relatively small, compared to the values generally found for adsorbed neutral polymers of comparable molecular weight and adsorbed amount. The one exception is with the very low charged (positive) surface, where more extended tails are thought to develop. The hydrodynamic thicknesses on the higher charged positive and negative surfaces are remarkably similar. The segment density profiles, in general, confirm the conclusions reached from the other studies here, that is of generally "fiat" configurations on highly charged (positive or negative) surfaces, with relatively short tai/s, and possibly the development of some loops at high ionic strengths, where intersegmental electrostatic repulsion is suppressed and the poly- electrolyte chains begin to approach the behavior of neutral polymers. © 1986 Academic Press, Inc. INTRODUCTION There have been relatively few studies of polyelectrolyte adsorption at charged solid/ solution interfaces, using well-defined systems, in comparison with the study of neutral poly- mer adsorption. However, research in this area has been stimulated, on the one hand by the recent availability of monodisperse polyelec- trolyte, such as poly(styrene sulfonate), and on the other hand, by developments on the theoretical side. In particular, van der Schee et al. (1-3) have extended the mean-field the- ories of Roe (4) for the adsorption of neutral polymers to polyelectrolytes. The obvious extra features to be considered in the adsorption of polyelectrolytes are the Presented at the 5th International Conference on Sur- face and Colloid Science, Clarkson University, Potsdam, N.Y., June 24-26, 1985, as part of a symposium entitled Protein and Polyelectrolyte Adsorption. Journal of Colloid and Interface Science, Vol. 111, No. 2, June 1986 charge on the polymer chain and the charge on the substrate surface. At very high ionic strengths these charge effects are screened out, and the systems behave essentially as neutral polymers; this is the base line for comparison. Decreasing ionic strength is akin to increasing the solvency, and of itself opposes adsorption because of the buildup of strong intra- and intermolecular repulsions of segments in loops or tails. The other main factor is then the ad- sorption free energy of segments in trains. There will be both "chemical" and electro- static contributions to consider here. In:this paper we report on the adsorption of mono- disperse sodium poly(styrene sulfonate) (PSS), a strong, anionic polyelectrolyte, onto poly- styrene latex particles, with either a positive surface charge (PS ÷) or a negative surface charge (PS-). Clearly in this case there is a strong hydrophobic contribution to the ad- sorption free energy, in addition to the elec- trostatic attraction/repulsion terms. 409 0021-9797/86 $3.00 Copyright © 1986 by Academic Press, Inc. All rights of reproduction in any form reserved.