EFFECT OF SURFACE GEOMETRY ON POLYMER ADSORPTION .2. INDIVIDUAL ADSORPTION AND COMPETITIVE ADSORPTION

Kinetics and isotherms of individual and binary mixtures of various polystyrenes (PS) with narrow molecular weight distributions on three porous silica surfaces have been investigated in cyclohexane and in carbon tetrachloride as a function of the ratio of the pore size to twice the radius of gyration of a PS chain in a bulk solution. Adsorption isotherms of the individual PS chains are of the high affinity type. When the size ratio is less than 2, the adsorbed amounts obtained at the plateau of the adsorption isotherms are less than those for the nonporous silica and decrease with a decrease in the size ratio. The rate at which PS chains attain equilibrium for the large pore ratio is much faster than that for the small one. The adsorbed amount is linear in the square root of time for the initial stage of the adsorption, suggesting that the initial stage is dominated by a diffusion process. The effect of solvent power on kinetics is more pronounced at higher initial concentrations. For the competitive adsorption, when both PS chains can penetrate easily into the pores, the shape of the adsorption isotherm resembles the high affinity type and the large PS adsorbs preferentially. By contrast, when the small PS adsorbs more than the large PS for the individual adsorption, the adsorption isotherm has a rounded shape.