Effect of annealing treatment on crystalline and dielectric properties of PVDF/PEG-containing ionic liquid composites

Abstract

To investigate the effect of poly(ethylene glycol)-containing ionic liquid (IL) and thermal annealing treatment on crystallization and dielectric relaxation behavior of poly(vinylidene fluoride) (PVDF), a series of PVDF/IL composites have been prepared using a solution-cast method. The interaction between imidazolium cation of ILs and >CF2 groups of PVDF can transfer nonpolar α phase to polar β and γ phase as a template at the primary crystallization, and then the interaction between PEG of ILs and >CF2 groups of PVDF can facilitate the PVDF chains in amorphous region to bring more polar phase and decrease the degree of crystallization for PVDF composites according to the template under thermal annealing treatment. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. In the frequency spectra of PVDF composites, dc conductivity, electrode and Maxwell-Wagner-Sillars (MWS) interfacial polarization resulted in high values of dielectric permittivity. The incorporation of ILs into the matrix and thermal annealing treatment can accelerate dc conductivity. The temperature dependence of relaxation time of dc conductivity follows the Arrhenius equation. The effect of annealing treatment on charge carrier movement mechanism was resulted from the increase of ion mobility induced by polymer chain segmental motion and polar phase crystals.