Time-Dependence of the Displacement Adsorption Behavior of Poly(methyl methacrylate) and Polystyrene System at the Solid-Liquid Interface as Studied by ESR

Abstract

ABSTRACT:The displacement adsorption behavior of poly(methyl methacrylate) (PMMA) and polystyrene (PS) system onto a nonporous silica surface from solution was studied by utilizing the ESR method. The fractions of train segments for these polymers were determined from the ESR spectra analyses, and these values were compared with those of the individual adsorption. When PS was preadsorbed on silica surface to saturation and then excess PMMA solution of known concentration was added and data taken as a function of adsorption time, the amount of PS desorbed from silica surface was found to increase proportionally with adsorption time until finally PS was completely replaced by PMMA. With the displacement ofPS from the silica surface, the amount of adsorption for PMMA which saturates the silica surface is obviously lower than that when adsorbed on silica surface individually; that is, the adsorbed PMMA has a flatter conformation than that in the individual adsorption. It also takes a long time for PMMA to adsorb on the silica surface compared with the individual adsorption, because a greater number of PS-silica surface attachments must be ruptured in order to effect displacement.KEY WORDS Displacement Adsorption I ESR I Polystyrene I Poly(methyl methacrylate) I Solid-Liquid Interface A number of techniques have been applied to the study of the polymers adsorbed at the solid-liquid interface. 1 -16 Among the molecular models proposed for characterizing polymer molecules adsorbed from solution onto a solid surface, a "loop-train-tail" model is now widely accepted. 1 In order to discuss the conformation of an adsorbed polymer molecule, it is important to estimate the fraction of train segments in all segments of the adsorbed polymer, p.Several studies have been reported on the competitive and displacement adsorption of polymers. 8 • 12 • 17 -28 Kawaguchi et a/. 23 studied the competitive and displacement adsorption of PS and poly(ethylene oxide) (PEO) and reported that PEO adsorbs preferentially over PS, and the preferential adsorption of large molecules over small molecules occurs even in the presence of different species. Thies 12 studied the competitive and displacement adsorption of PS and PMMA mixtures from trichloroethylene solution using IR spectroscopy. He reported the reversibility of adsorption processes in such systems. The present authors 8 reported the competitive adsorption behavior of PS and PMMA mixtures and discussed the conformation of both adsorbed polymers under this condition. We also discussed the difference in the adsorption ability of styrene and methyl methacrylate on the silica surface.