Adsorption of polystyrene and poly(methyl methacrylate) onto a silica surface studied by the infrared technique. Comparison with theory

Abstract

Adsorption of polystyrenes (PS) and poly(methyl methacrylate)(PMMA) onto a non-porous silica (Aerosil 130) in trichloroethylene at 25 °C has been studied using IR and UV spectroscopies. Three important quantities, namely the amount adsorbed, A, the fraction, θ, of the silanol groups occupied by polymer chains, and the fraction, p, of the polymer repeating unit which is directly attached to surface silanol groups, have been determined. Adsorption isotherms of both polymers are the high-affinity type. The plateau-adsorbed amounts increase slightly with increasing molecular weight of the corresponding polymer. The plateau θ values for both polymers are independent of the molecular weight, while the plateau p values decrease with increasing molecular weight. The experimental data for A, θ, and p are compared with the theory of Scheutjens and Fleer based on a lattice model. They could be interpreted quantitatively by selecting the adsorption energy parameter X_s= 0.42 for PS and X_s= 1.4 for PMMA. The difference in the X_s parameter between PMMA and PS is mainly attributed to the more polar character of PMMA compared to PS.