Effect of substrate interface on mechanical relaxation behavior in polymer ultrathin films

Mechanical relaxation behavior of polystyrene (PS) and poly (2-vinylprydine) (P2VP) thin and ultrathin films on substrates was examined. Even in the case of the ultrathin films, the α₂-relaxation process corresponding to the segmental motion was successfully observed. However, the α_a-absorption peak was broadened toward lower and higher temperature sides because of surface and interfacial effects. Interestingly, when a PS ultrathin film was sandwiched between SiO_x layers, an additional peak come up with the interfacial segmental motion appeared at the higher temperature side. In the case of the P2VP ultrathin films on the SiO_x substrates, the interfacial effect became remarkable due to the strong attractive interaction between chains and the substrate. Finally, it was concluded that chain mobility in the interfacial region was depressed in comparison with that in the internal bulk phase.