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 gamma-PVDF films with a wide range of thickness based on the spontaneous diffusion of ionic liquids (ILs) into the alpha-PVDF matrix. It involves three steps: (i) preparation of alpha-PVDF films, (ii) surface coating of the resultant alpha-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 alpha-PVDF film is then transferred into a gamma-rich one through the well-known alpha-gamma' phase transition. The alpha-gamma' transition is found to be much faster and more efficient for high-temperature prepared samples. It has been further confirmed that the alpha-gamma' 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 degrees C.