Polyelectrolyte adsorption on oxides .1. Kinetics and adsorbed amounts

We have investigated the adsorption of strong polyelectrolytes (quaternized polyvinylpyridine (PVP+) and quaternized dimethylaminoethyl methacrylate (AMA(+))) and of a weak polyelectrolyte (AMA) onto TiO2 and SiO2, using reflectometry. Two characteristic properties, i.e., the initial adsorption rate and the amount adsorbed, were studied as functions of ionic strength and pH. Also, the effects of the molar mass of the polymers, of the type and valence of the ions, and of the surface charge and the segment charge were investigated. We find that the initial adsorption rate is usually determined by the rate of transport to the surface, and therefore by the diffusion coefficient, which depends on the size of the molecule. The amount adsorbed is determined by a balance between the interactions in the system. For PVP+ adsorbing on TiO2, these interactions are mainly electrostatic, but on SiO2 a nonelectrostatic affinity of PVP+ for the surface also plays a role, The adsorption of AMA(+) and AMA on TiO2 is purely electrostatic. Upon adsorption of AMA(+) the surface adjusts its charge. In the case of adsorption of AMA both the surface and the segment charge are regulated. This regulation process reduces the buildup of the electrostatic potential on the surface and enables more polymer molecules to adsorb. (C) 1996 Academic Press, Inc.