The annealing of solution grown crystals of alpha and gamma poly(vinylidene fluoride)

Abstract

Single crystals of poly(vinylidene fluoride) PVF2 have been grown from dilute solution and sedimented to form oriented mats. The product was α-PVF2 or a mixture of α- and γ-PVF2 and different morphologies were observed for the two phases. Annealed mats exhibited complex melting behavior, due in part to melting and recrystallization. Plots of melting temperature against reciprocal lamellar spacing indicate equilibrium melting points of 443.5 and 457.3 K for rapidly crystallized α- and γ-PVF2 after 1-h anneal, and fold surface free energies of 15.6 and 27.2 mJm−2 for α-PVF2 from different solvents, 24.8 mJm−2 for γ-PVF2. Long annealing times or high annealing temperatures tend to increase the melting point without changing the lamellar thickness probably due to rejection of head-to-head defects.