Towards comprehensive understanding of piezoelectricity and its relaxation in VDF-based ferroelectric polymers

Piezoelectric resonance spectroscopy was employed to elucidate the microscopic mechanisms of piezoelectricity and its relaxation for the uniaxially-drawn and poled films of polyvinylidene fluoride and the vinylidene fluoride/trifluoroethylene copolymer with a composition of 75/25 mol. The former was...

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Bibliographic Details
Published in:Polymer (Guilford) 2023-09, Vol.283, p.126235, Article 126235
Main Authors: Furukawa, T., Kodama, H., Ishii, H., Kojima, S., Nakajima, T., Gan, W.C., Velayutham, T.S., Majid, W.H. Abd
Format: Article
Language:English
Subjects:
Dielectric relaxation
Ferroelectric polymer
Piezoelecric resonance
Poly(vinylidene fluoride)
VDF/TrFE copolymer
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Summary:Piezoelectric resonance spectroscopy was employed to elucidate the microscopic mechanisms of piezoelectricity and its relaxation for the uniaxially-drawn and poled films of polyvinylidene fluoride and the vinylidene fluoride/trifluoroethylene copolymer with a composition of 75/25 mol. The former was semicrystalline whereas the latter consisted of extended-chain crystals. Accurate measurements of dielectric frequency spectra in the mHz-to-GHz range revealed piezoelectric resonance superimposed on broad dielectric relaxation. Analyses of the resonance spectra of the length, width and thickness vibrations allowed for evaluation of all elastic and piezoelectric tensor components. The single-crystalline copolymer substantiated the crystalline relaxation associated with intramolecular rotational fluctuations of trans segments and longitudinal chain softening. The most informative were the piezoelectric e31, e32, and e33 constants expressing the charge responses induced by chain elongation, interchain separations parallel and perpendicular to thickness, respectively. It was found that e31 showed relaxation from small negative to large positive, and e33 was much larger than e32 both being negative and non-relaxational. These results were discussed in reference to those of Form I crystals whose polar axis was π/6 tilted due to (110) twin. We identified three microscopic mechanisms (i) elongation of relaxing chain reduces the effective monomer dipole moment μ due to reduction of rotational fluctuations, (e31 > 0), (ii) the increase in interchain distance reduces μ due to decrease in positive local field, (e32, e33 
ISSN:0032-3861
1873-2291
DOI:10.1016/j.polymer.2023.126235