Ionic Liquid Assisted α–γ′ Phase Transition of Poly(vinylidene fluoride) Thin Films

In this work, a simple and efficient approach has been developed for preparing γ-PVDF films with a wide range of thickness based on the spontaneous diffusion of ionic liquids (ILs) into the α-PVDF matrix. It involves three steps: (i) preparation of α-PVDF films, (ii) surface coating of the resultant α-PVDF films with ionic liquids or quaternary ammonium solution, and (iii) annealing the surface modified PVDF thin film at a high temperature. In this way, the original α-PVDF film is then transferred into a γ-rich one through the well-known α–γ′ phase transition. The α–γ′ transition is found to be much faster and more efficient for high-temperature prepared samples. It has been further confirmed that the α–γ′ phase transition includes the induction and slow phase transition stages for low-temperature fabricated samples as well as the rapid and then slow transition stages for the samples prepared at 120 and 150 °C.