Transmission Electron Microscopic Observation on Phase Transition Caused in Poly (vinylidene fluoride) Single Crystal by Annealing under High Pressure

In solution-grown α-form single crystal of poly (vinylidene fluoride) (PVDF), solid to solid phase transitions (α→γ and γ→β) by annealing under high pressure have been found by transmission electron microscopic (TEM) observation. The γ-form is produced at temperatures higher than 508 K and at 320 MPa from the original α-form crystal. The γ→β transition occurs at temperatures higher than 513 K and at pressures higher than 350 MPa. It is accompanied by striations (30∼40 nm wide) along the b -axis of the γ-phase due to partial thickening, which disappear with the completion of the γ→β transition.