Molecular-Weight Dependence of the Polymer Adsorption at Solid-Liquid Interfaces as Studied by ESR Spectroscopy

The conformation of poly(methyl methacrylate) adsorbed from dilute solution on nonporous silica was investigated by ESR method using three-component spectrum analysis. The fraction of the polymer segments in train, short loop, and long loop or tail, as well as the rotational correlation time for the segments were examined with regard to molecular weight (M=103–3×106), the degree of adsorption, and the particle size of silica. In CCl4, the saturation adsorption, As, increased from 6 to 16×10−8 g cm−2, the fraction of polymer segments in train, p, decreased from 0.9 to 0.4, and the segment mobility reduced with the increase in molecular weight, respectively. Remarkable changes in As and p were found in a range of molecular weight of 5×104. In benzene, the values of As and p were less dependent on molecular weight than the cases of adsorption in CCl4. Marked effects of intrachain interactions on the conformation were revealed for the adsorption of coiled polymers with high molecular weight from CCl4 solution at low degrees of adsorption, where the loop formation was observed for polymers of M>104. The intrachain force was attributed to overlapping among the segments. The difference in the adsorption behavior between the cases in CCl4 and benzene was interpreted by the difference in the degree of deformation of polymer molecules upon adsorption.