Segmental Dynamics in Poly(Methyl Acrylate)-d3 on Strongly and Weakly Adsorbing Silica Surfaces
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The segmental dynamics of a polymer on a solid surface appears to be significantly different than that in bulk. The strength of the interaction between polymer segments and a solid surface is likely to be an important factor affecting the segmental mobility of the polymers. Studies of polymers on a weakly adsorbing surface would provide additional understanding of their motional characteristics on surfaces. In a recent NMR study by Rivillon et al., chain dynamics was seen to be different for samples, even when there was no specific interaction with the surface. Peanasky et al. have found a restricted segmental dynamics for the polyphenylmethylsiloxane samples at weakly adsorbing surfaces. Zheng et al. Observed a significant difference from bulk dynamics on both strongly and weakly interacting interfaces for poly(styrene) (PS) and poly(2-vinylpyridine). Mechanical properties of weakly interacting poly(methyl acrylate) (PMA)- silica composites were seen to become poorer than the ones with stronger interactions. Contrasting results for PS on silicon surfaces with X-ray reflectivity also highlighted the importance of the surface-polymer interaction for thin films.5,6 Wallace et al. explained that the contrasting results were due to a difference in the surface characteristics. A stronger surface-polymer interaction on a hydrogen-terminated silicon resulted in an increase in glass transition temperature (Tg) for thin films of PS, while Keddie et al.â s work on a silicon native-oxide surface with the same polymer indicated a decrease in Tg for thin films due to a weaker interaction. The segmental dynamics of PMA-d3 on a strongly adsorbing surface was previously studied using the deuterium (2H) quadrupole-echo NMR and modulated differential scanning calorimetry. In this study, the segmental dynamics of PMA on a weakly adsorbing surface was investigated with 2H quadrupole-echo NMR and compared to that in bulk and on a strongly adsorbing surface.