Colloidal Crystallization and Ionic Liquid Induced Partial β-Phase Transformation of Poly(vinylidene fluoride) Nanoparticles

Colloidal crystallization of poly(vinylidene fluoride) (PVDF) nanoparticles (NPs) and its β-phase transformation were studied. The pristine PVDF NPs with an average diameter of 230 nm consist of 46% α-phase and 54% amorphous PVDF. The PVDF NPs were assembled on a quartz substrate by means of vertical deposition method from a tetrahydrofuran dispersion of PVDF NPs with a few volume percentage of n-alkane. The resultant colloidal thin films displayed a pale-greenish structural color with the selective reflection at around 550 nm wavelength due to closely packed PVDF NPs. The colloidal thin films were immersed into an acetonitrile solution containing 2 wt % ionic liquid, subsequently air-dried, and thermally annealed at 140 °C, just below the melting point of the PVDF–IL blends. After annealing, the PVDF NPs partially transformed into its β-phase with the volume percentages of α-, β-, and amorphous phases of 22, 32, and 46%, respectively. The postannealed colloidal films still maintained the face-centered-cu...