Study On Crystal Controllable And Mechanism Of Poly(vinylidene Fluoride)(PVDF) Modified By Functional Ionic Liquid And Graphene

In this work, the imidazolium ionic liquid oligomer contained linear PEG chain,graphene(Gra) modified by the copolymer with 1-vinyl-3-ethyl imidazole bromine and methyl methacrylate and Gra modified by ionic liquid with long alkyl chain were mixed into poly(vinylidene fluoride)(PVDF) through the solution mixing and vacuum hotpressing, high content polar phase and performance of films were prepared. The influence on crystal type and properties of PVDF brought from functional ionic liquid and ionic liquid copolymer were investigeted systematically, in additon, the crystallization kinetics were employed to character the crystallization mechanism. The paper research includes three parts mainly:(1) the incoporation of the imidazolium ionic liquid oligomer contained linear PEG chain into PVDF, the interaction between the imidazolium cation of ionic liquid and >CF2- of polymer chain can promote the content of β/γ phase. And the interaction between PEG chain and >CF2- of polymer chain can facilitate the PVDF chain in amorphous region to fold into polar phase according to the original crystal template under the annealing treatment. The effect of ionic liquid and heating treatment can strengthen the DC aonductance and MWS polarization. MWS polarization, ion polarization and DC conductance can promote the dielectric constant through dielectric frequency spectrum of PVDF blends.(2) A copolymer (P[MMA-IL]) with 1-vinyl-3-ethyl imidazole bromine (IL) and methyl methacrylate (MMA) was synthesized by radical polymerization technique.DSC results indicated P[MMA-IL] modified Gra can promote the Tc and Tm of PVDF because of the appearance of β polar crystal. The Gra were modified by P[MMA-IL]as a template to increase the degree of crystallinity of PVDF. XRD and FTIR-ATR results confirmed that P[MMA-IL] can promote the content of β-crystal due to the electrostatic interaction between the >CF2- of the polymer backbone and imidazolium cation, and the strong induction was brought by the template of Gra. POM photos displayed that α-crystal with loose structure because the MMA chain segment was embedded into the chip space of spherulites. the electrostatic interaction and nucleating agent of IL chain segment result to β crystal with small size and increase the crystallization rate. Dielectric properties research showed that PMMA and modified Gra can reduce the crystallinity and concentration of PVDF chain, leading to weak interface polarization and orientation polarization of PVDF, hence, the dielectric constant is low. While P[MMA-IL] and modified Gra can induce more β crystal. And the strong interface polarization enhanced by β crystal and ion polarization of IL chain segment can improve the dielectric constant.(3) To investigate the effects of Gra modified by 1-hexadecyl-3-methylimidazolium bromide on the crystallization kinetics behaviour of PVDF. Crystallization kinetic parameters, such as relative crystallinity (Xt), crystallization half time (t1/2),crystallization rate constant (Z), Avrami exponents (n) and activation energy (Ea) have been determined by both isothermal and non-isothermal techniques. In the isothermal and non-isothermal crystallization process, for PVDF/0.5IL/0.5Gra, ionic liquid and Gra can facilitate nucleation to decrease Ea, synergistic efforts of the ionic liquid and Gra can maintain appropriate crystallization rate to form β phase extruded form a phase.The positive effect on the crystallization of PVDF may be ascribed to not only due to the existence of Gra-cation interaction between the imidazolium cation and the aromatic carbon ring structure, but also due to the electrostatic interaction between the >CF2-groups of the polymer backbone and imidazolium cations.