The Crystal Structure of the γ Phase of Poly(vinylidene fluoride)

Abstract

The crystal structure of the y phase of poly(vinylidene fluoride) (PVF2) was determined by X-ray diffraction techniques. Oriented specimens of the y phase were obtained by high-temperature drawing of films of ultrahigh molecular weight PVF2 cast from dimethylacetamide solution. The unit cell of the y phase was found to be orthorhombic with dimensions a = 0.497, b = 0.966, and c = 0.918 nm. The chain conformation is approximately TTTGTTTG'. Individual chains with this conformation possess a net electrical dipole and pack such that the unit cell is polar. The chains pack in a statistical parallel-antiparallel manner, which can be modeled by a hypothetical four-chain unit cell belonging to space group C2cm.Four crystal forms of poly(vinylidene fluoride) are known. The a phase, or phase II, is the form produced

Thermal Analysis of Phase Transitions and Crystallization in Polymeric Fibers

“…An overview of the crystalline phases, together with the conditions for their formation, is given in Table 2. Crystalline phases of poly(vinylidene fluoride) [34][35][36][37] If the material is present in the phase, it can be used to create sensors or actuators, which are commonly used in the form of films in microphones, hydrophones or headphones. Here, the necessary process conditions (drawing of the films or high electric fields) for the phase formation are well known [31,38].…”

Spin cast ferroelectric beta poly(vinylidene fluoride) thin films via rapid thermal annealing

“…The heat treatment above T m of PVDF always produced either ␥ or ␣ crystals regardless of the heating rate as confirmed by both our recent work and others. 8,11 The melting and quenching methods, known as an effective way for ␤ crystal formation in micron thick PVDF film, 12 dominantly generated ␣ crystals in our thin films.…”

Development of a fiber structure in poly(vinylidene fluoride) by a CO2 laser-heated drawing process

“…In particular, PVDF fiber can be melt-spun to form a fishing line because of its low water absorption, low refractive index similar to that of water, high specific gravity and good resistance to degradation by light. PVDF has been identified to take on five crystalline forms: a, b, g, d and e. [1][2][3][4] The a form (form II) is formed by cooling a quiescent melt, and it forms a nonpolar pseudo-orthorhombic structure containing two chains of tg + tg À conformation. Mechanical drawing of the a-form produces the b form (form I) containing two all-trans chains.…”