A Hidden Relaxation Process in Poly(2-vinylpyridine) Homopolymers, Copolymers, and Nanocomposites

Abstract

In broadband dielectric spectroscopy experiments, we find that introducing an air gap between the top electrode and the polymer sample reduces DC conductivity substantially, allowing the study of low-frequency relaxations, whose signal would otherwise be hidden by the DC conductivity signal. An extra process slower than the α-relaxation process is observed in poly(2-vinylpyridine) (P2VP), consistent with some earlier reports. This “slower process” was studied in two heterogeneous systems to examine the interaction between the 2VP and other species to elucidate the mechanism behind the slower process signal. In a random copolymer of styrene and 2VP, the relaxation strength of the slower process relative to the α-process increases substantially at low 2VP mole fractions. Additionally, in a composite of P2VP and octa(aminophenyl) silsesquioxane (OAPS), the presence of OAPS increases both the strength and timescale of the slower process, leaving the α-relaxation process relatively unchanged. This suggests that the slower process could be caused by cooperative polymer relaxation coupled to the transport of heterogeneous components and impurities. Further studies are needed to probe the molecular-level mechanism of this slower process and its effect on interfacial properties.