EFFECT OF SURFACE GEOMETRY ON POLYMER ADSORPTION .3. COMPETITIVE ADSORPTION AT THE THETA POINT

Adsorption isotherms of binary mixtures of polystyrenes (PS) with narrow molecular weight distributions and a polydisperse PS on porous and nonporous silica surfaces have been measured in cyclohexane. For the adsorption of the binary mixture on the porous silica, when both PS chains can penetrate into the pores without significant deformation, a complete preferential adsorption of the large PS chain over the small one is observed at the plateau in the adsorption isotherm and the adsorption isotherm has a rounded shape. By contrast, when the large PS component in the mixture adsorbs more than the small PS component at the plateau, i.e., incomplete preferential adsorption, the total amount adsorbed at the plateau is larger than that for the complete preferential adsorption. Furthermore, its magnitude is the same as for the adsorption of the corresponding mixture on the nonporous silica as well as the adsorption of polydisperse PS on the porous and nonporous silicas.