DFT study of the structure, conformation, reactivity and electronic properties of β-P(VDF-co-TrFE) copolymer

Abstract

Poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-co-TrFE), is the most important member of the PVDF copolymer family because the additional fluorine atom of the TrFE unit stabilizes the all-trans, ferroelectric β-phase directly from the melt. Here, density functional theory (DFT) calculations at the B3LYP/6-311++G(d, p) level were used to study the structure, conformation, electronic structure and reactivity of β-P(VDF-co-TrFE) oligomers across the full TrFE composition range (0–100 mol%), using an eight-unit oligomer identified from an energy-convergence analysis over 1–20 monomer units. The optimized geometries confirm an all-trans β-phase backbone, and the rotational-energy profile shows that both VDF and TrFE dimers favour trans conformations, with TrFE exhibiting higher rotational barriers. The HOMO-LUMO gap narrows from 10.01 eV (0% TrFE) to 8.35 eV (100% TrFE). Conceptual DFT descriptors indicate that TrFE-rich segments are softer, more electronegative and more electrophilic than VDF-rich segments. Simulated FTIR and XRD patterns confirm the β-phase fingerprint for all compositions. The computed single-chain dipole moment and polarity peak near 50 mol% TrFE, indicate that near-alternating VDF-TrFE sequences give the strongest intramolecular dipole reinforcement. Because the macroscopic piezoelectric response is additionally controlled by crystallinity, domain structure and a morphotropic-phase-boundary-like competition between the trans-planar and 3/1-helical phases, these isolated-chain descriptors are offered as molecular-level design guidance for ferroelectric P(VDF-TrFE) rather than as a direct prediction of device performance in energy-harvesting, sensing and flexible-electronics applications. β-P(VDF-co-TrFE) is studied by DFT across the full 0–100 mol% TrFE range. Optimized geometry, FTIR and XRD confirm the all-trans β-phase at all ratios. HOMO-LUMO gap narrows from 10.01 to 8.35 eV as TrFE content increases. Single-chain dipole and polarization density peak near 50 mol% TrFE. TrFE-rich segments are softer, more electronegative and more electrophilic. β-P(VDF-co-TrFE) is studied by DFT across the full 0–100 mol% TrFE range. Optimized geometry, FTIR and XRD confirm the all-trans β-phase at all ratios. HOMO-LUMO gap narrows from 10.01 to 8.35 eV as TrFE content increases. Single-chain dipole and polarization density peak near 50 mol% TrFE. TrFE-rich segments are softer, more electronegative and more electrophilic.