Dynamics of Interfacial Polymers in Composites
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Much experimental and theoretical work has been done on the behavior of adsorbed polymers. However, not much work has focused on the dynamics, especially segmental dynamics, of the adsorbed polymers. This is especially true of filled polymer or composite systems as the interfacial layers in these systems are difficult to study with most techniques. NMR is not restricted to use in optically clear samples and its use in the characterization in the surface polymers has been reviewed. In our laboratory, we have found that deuterium NMR could be used to probe the segmental dynamics of adsorbed polymers. The position of the deuterium label (selective deuteration) ensured that information on only certain moieties will be obtained. We have used solid-state deuterium NMR to probe the behavior of block copolymers and homopolymers on surfaces. We have suggested that for poly (vinyl acetate)-d3 (PVAc-d3) and poly (methyl acrylate)-d3 (PMA-d3) homopolymers at the silica-polymer-air interface that a motional gradient exists. This motional gradient includes regions where the segmental mobility was lower and higher than that of the bulk polymer. The lower the mobility segments were identified to be due to segments at or near the polymer segments at the polymer-air-interface. In the present study, we report the effect of a polymer overcoat on the segmental dynamics of the PMA-d3 adsorbed on silica. We believe that this situation is very similar to that found in a filled polymer composite. We find that the presence of the polymer over layer changes the dynamics of the original layer on the surface. The advantage of these experiments is that the originally adsorbed polymers are deuterated while the overcoat polymers are hydrogenated. Since deuterium NMR “sees” only the deuterated polymer, we directly probe the interfacial material.