Simulation of α- and β-PVDF melting mechanisms

Abstract

Molecular dynamics (MD) simulations have been used to study the melting of α-and β-poly (vinylidene fluoride) (α-and β-PVDF). It is seen that melting at the ends of the polymer chains precedes melting of the bulk crystal structure. Melting of α-PVDF initially occurs via transitions between the two gauche dihedral angles (G ↔ G') followed by transitions between trans and gauche dihedral angles (T ↔ G/G'). Melting of β-PVDF initially occurs via T → G/G' transitions and via transitions of complete β-(TTTT) to α-(TGTG') quartet. The melting point of β-PVDF is higher than that of α-PVDF, and the simulated melting points of both phases depend on the length of the polymer chains used in the simulations. Since melting starts at the chain ends, it is important to include these in the simulations, and simulations of infinitely long chains yield melting points far larger than the experimental values (at least for periodic cells of the size used in this work), especially for β-PVDF. The simulated heats of fusion are in agreement with available experimental data.

PVDF-PAni blend: a free-standing film with variable electrical resistance

“…In addition, the low value for the Young's modulus of the pure PVDF can be attributed to the processing of the material, where the material was cooled rapidly to the sudden freezing of the chains and trapping of the PAni particles, to prevent the segregation of phases. In this situation, there was no sufficient time for the recrystallization process to occur efficiently, and the blend was less rigid [5,6]. However, the material showed a higher breaking strain of around 120 %.…”

“…The advantage of the use of polyaniline (PAni) instead of conductor particles, like carbon black, is the control of the electrical conductivity of the PAni by protonation/deprotonation, through the control of the pH of the organic or aqueous solution [4]. Polyvinylidene fluoride (PVDF) was chosen as a polymer matrix, due to its excellent mechanical properties, and because it can be processed without an organic solvent, since it is a crystalline thermoplastic [5,6].…”

Insight of electrical behavior in ferroelectric‐semiconductor polymer nanocomposite films of PVDF/ZnSe and PVDF/Cu:ZnSe

“…β‐phase of PVDF films can be obtained by stretching, applying high pressure, and high electrical field from α‐phase . Many studies, on the structure and electrical applications of α, β, and γ‐phase PVDF crystals have been performed and most current research focuses on enhancing the β‐ and γ‐phases in PVDF in order to achieve the desired applications . The nanocomposite thin films of PVDF with inorganic materials such as Cu, TiO 2 , ZnO, CuS, BaTiO 3 , ferrite, graphene, graphite, and zeolite to achieve various performance objectives.…”

Molecular dynamic study of dielectric polarization and ferroelectricity in a model polar polymer

“…The electrical responses of PVDF and PVDF‐related polar and ferroelectric polymers arranged in ideal crystal lattices with periodic boundary conditions have been widely studied with molecular dynamic methods . There have also been more limited electrical and mechanical molecular dynamics‐based studies of amorphous and simple mixed‐phase morphologies (including melting) in such polymers . In realistic semicrystalline polymers, the actual morphology is quite complex.…”

“…[21][22][23][24] There have also been more limited electrical and mechanical molecular dynamics-based studies of amorphous and simple mixed-phase morphologies (including melting) in such polymers. [25][26][27][28][29] In realistic semicrystalline polymers, the actual morphology is quite complex. Typically there are spherulites on the largest scale, and within them, ensembles of lamellar structures of folded polymer chains.…”