Polymeric systems show various types of dynamical processes. Although broadband dielectric spectroscopy (BDS) can reveal the nature for most of the processes, some processes are totally covered with the contributions from the DC conductivity, and as a result, the detailed properties of such hidden processes are usually hard to be accessed by BDS except the derivative method of the real part of dielectric permittivity. Recently we have found 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.<br/>In this presentation, we would like to show an interesting example, that is, poly(2-vinylpyridine) (P2VP) homopolymers, copolymers with styrene, and nanocomposites with octa(aminophenyl) silsesquioxane (OAPS)~[1]. In this polymeric systems, an extra process slower than the α-relaxation process can clearly be observed in the imaginary part of the dielectric permittivity, 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 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.<br/>Air gap method can reduce the contributions from DC conductivity. At the same time, there might be a possibility of the emergence of an extra peak due to the interfacical polarization, which is usually called Maxwell-Wagner-Sillar (MWS) process. To discuss such possibility, we have also applied the derivative method to the real dielectric permittivity to obtain the imaginary dielectric permittivity without the effect of DC conductivity. Comparing the above results with this ones, we would like to discuss a possible nature of the slower process.

Dielectric study of relaxation process in nanocomposites of poly(2-vinylpyridine) and small particles

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