Molecular Conformation and Packing of Poly(vinylidene fluoride). Stability of Three Crystalline Forms and the Effect of High Pressure

Abstract

The formation of three crystalline forms of poly(vinylidene fluoride) was studied in detail by using an apparatus for heat treatments under high pressure up to 5000 atm. Form II consisting of TGTG-type molecular chains was the most stable under atmospheric pressure, and form I, composed of planar zigzag-type chains, was formed under special conditions, such as tension, high pressure, etc. Form III may be an intermediate modification between I and II. Based upon these experimental facts, as well as the potential energy calculations of the intra-and intermolecular interactions in the crystal lattices due to the van der Waals and electrostatic forces, the relation between the conditions of formation of the three forms and their structures was examined. The planar zigzag-type conformation (in forms I and III) is considered to be less stable than the TGTG type (form II) because of the steric hindrances and electrostatic dipole interactions. In spite of the difference in the intramolecular potential energy between these two molecular conformations, the stabilities of the three crystalline forms are not so very different because of the more favorable intermolecular interaction in form I.

Quantum Chemical Investigations of Structural Parameters of PVDF-based Organic Ferroelectric Materials

“…The Tp conformation of the all-trans phase, has a highly polarized backbone with the highest spontaneous polarization in a unit crystal cell (Jungnickel, 1999). This spontaneous polarization gives the special ferroelectric properties, leading to a broad potential of application in several newtechnology electronics, such as in sensors, transducers, energy storage devices, communications and microphones (Kawai, 1969;Lovinger, 1983;Jungnickel, 1999;Lando et al, 1966;Farmer et al, 1972;Hasegawa et al, 1972;Karasawa & Goddard, 1992;Tashiro et al, 1995;Nalwa, 1995;Lang, 2006;Wang et al, 1988). A drawback, however, of the synthesized β-PVDF pure material, is that the maximum crystallinity reached is 50%, which results in lower polar properties than those of pure Tp phase, if formed.…”

The Flory-Huggins Interaction Parameter and Thermoreversible Gelation of Poly(vinylidene fluoride) in Organic Solvents

“…Another methods for obtaining these crystalline structures have been also reported. [1][2][3][4][5][6] According to the polarity of the bonds between the relatively electron-rich CH 2 carbon atoms and the relatively electron-poor CF 2 carbon atoms, the repeating unit CF 2 CH 2 of PVdF chain has a dipole moment. 7 As the PVdF polymer shows the ferroelectric behavior, 1 there is much current interest in solution-casting techniques for fabricating this polymer for sonar and acoustic devices.…”

A Review on Polymer Crystallization Theories

“…For instance, polyvinylidene difluoride [120,121], polytetrafluoroethylene [122], polychlorotrifluoroethylene [123], trans-1,4-polybutadiene [124][125][126][127], and polyethylene terephthalate [128][129][130].…”