Influence of Graphene Oxide on Crystallization Behavior and Chain Folding Surface Free Energy of Poly(vinylidenefluoride-co-hexafluoropropylene)

Graphene oxide (GO) filled poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HPF) copolymer nanocomposites as promising piezoelectric materials are developed, and their crystallization behavior and chain folding free energy are examined. Appropriate distribution of GO nanoparticles in the copolymer is confirmed by transmission electron microscopic analysis. The crystalline structure of nanocomposites is analyzed by wide-angle X-ray scattering and Fourier transform infrared spectroscopy. The results show an increase in the beta-phase content of PVDF-HPF copolymer in the presence of GO. Non-isothermal crystallization kinetics of the neat polymer and corresponding nanocomposites are studied by a multiple heating rate differential scanning calorimetry using modified Avrami-Jeziorny and Liu models. Moreover, barrier energy of crystallization is calculated by Friedman and Kissinger models. It is found that addition of GO to the copolymer increases nucleation activity of the nanocomposites. Investigation on linear crystal growth via Hoffman's theorem indicates an enhanced nucleation activity upon increasing GO content. The surface folding free energy of the neat polymer is changed from 5.79 x 10(-2) to 7.27 x 10(-2) J m(-2) upon addition of 5 wt% of GO. A bundle-like mechanism is proposed, which can explain the crystallite growth. Analysis based on Vyazovkin theorem reveals that the crystallization activation energy is independent of GO at elevated temperatures.