Morphology, structure, rheology, and thermodynamics of piezoelectric poly(vinylidene fluoride)-ethylene carbonate thermoreversible gel

Dasgupta, D. ; Manna, S. ; Garai, A. ; Dawn, A. ; Rochas, C. ; Guenet, J. M. ; Nandi, A. K. (2008) Morphology, structure, rheology, and thermodynamics of piezoelectric poly(vinylidene fluoride)-ethylene carbonate thermoreversible gel Macromolecules, 41 (3). pp. 779-787. ISSN 0024-9297

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ma7021502

Related URL: http://dx.doi.org/10.1021/ma7021502

Abstract

Poly(vinylidene fluoride) (PVF2) produces a thermoreversible gel with the important solvent, ethylene carbonate, which is used as a dispersing medium in a lithium ion battery. This is evidenced from the fibrillar network morphology and reversible first-order phase transition of the gels. The invariance of the storage and loss modulus with frequency at lower temperatures (≤110 °C) and the existence of a crossover point between them at higher temperatures further supports thermoreversible gel formation in the system. Solvent subtracted FTIR spectra of the gels indicate formation of a β polymorph, which is retained even after drying using cyclohexane as a guest solvent. The wide-angle x-ray scattering (WAXS) diffractogram of the dried gel also indicates formation of the piezoelectric β polymorph, giving a first time report of thermoreversible piezoelectric gel formation. The temperature-concentration phase diagram in conjunction with Tamman's plot indicates the presence of a polymer-solvent molecular compound whose stoichiometry is around 1.2 solvent molecules/monomer unit. The presence of eutectic and metatectic transitions in the PVF2- ethylene carbonate (EC) system is also evidenced from the phase diagram. Time-resolved X-ray diffraction patterns also show a new peak at q =13.15 nm-1 which is assigned to the molecular compound on the basis of a possible crystalline lattice. Molecular modeling using molecular mechanics calculations with the MMX program supports polymer-solvent complex formation. It also indicates that electrostatic and H-bonding forces are operating side by side on the carbon skeleton fixing the all trans chain conformation of β PVF2 in the gel.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:24097
Deposited On:29 Nov 2010 10:27
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