First-principles studies of spontaneous polarization in mixed poly(vinylidene fluoride)/2,3,3,3-tetrafluoropropene polymer crystals

Abstract

Spontaneous polarization P of mixed polymer crystals based on β poly(vinylidene fluoride) (PVDF, –CH₂–CF₂–) and 2,3,3,3-tetrafluoropropene (TFP, –CH₂–CF(CF₃)–) was evaluated for β-PVDF/iso-PTFP, β-PVDF/P(VDF-alt-iso-TFP) and β-PVDF/syndio-PTFP. A plane-wave-based density-functional theory (DFT) approach, combined with the Modern Theory of Polarization formalism utilizing maximally-localized Wannier functions for calculating P, indicates that all systems exhibit similarly high or even slightly larger polarization than that of perfectly crystalline β-PVDF (0.18 C m⁻²). These properties stem from the substantial dipole moment of the TFP unit, which is estimated to be ∼2.3 D in an isolated chain, but is enhanced to ∼2.8 D in the crystal.