Quantitative study on the face shear piezoelectricity and its relaxation in uniaxially-drawn and annealed poly-l-lactic acid

Zin, S. H. Mat and Velayutham, Thamil Selvi and Furukawa, T. and Kodama, H. and Gan, W. C. and Chio-Srichan, Sirinart and Kriechbaum, M. and Nakajima, T. (2022) Quantitative study on the face shear piezoelectricity and its relaxation in uniaxially-drawn and annealed poly-l-lactic acid. Polymer, 254. ISSN 0032-3861, DOI https://doi.org/10.1016/j.polymer.2022.125095.

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Piezoelectric resonance spectroscopy was used to evaluate the face shear piezoelectricity and its relaxation for structurally controlled poly-L-lactic acid (PLLA) films. We prepared samples by uniaxial drawing at 80 degrees C for a ratio of 2-6 and annealed at temperatures above glass transition (Tg = 60 degrees C) to below melting (Tm = 170 degrees C) for 1 hour. The degrees of crystallinity Xc and orientation Fc by X-ray diffraction were controlled over a broad range to reach Xc = 0.8 and Fc = 0.9. We measured broadband dielectric spectra where the piezoelectric resonance was observed superimposed on dielectric relaxation. Analyses of the resonance spectra for 45 degrees -cut square sample resulted in the determination of the face-shear piezoelectric constants e14 and d14, as well as the elastic shear compliance s44 and stiffness c44. At room temperature, e14 was shown to be proportional to a product of Xc*Fc, whereas d14 demonstrated saturation due to an increase in c44. By extrapolating to Xc*Fc =1, the e14 of PLLA crystal was determined. As the temperature increases, piezoelectric relaxation due to non-crystalline segmental motion was observed as well as dielectric and elastic relaxation. It was found that e14 decreased in a similar manner to c44 whereas d14 increased slightly with increasing temperature. The temperature dispersions of e14, d14 and c44 were reproduced using an equivalent three-spring model consisting of a crystalline piezoelectric spring connected by series and parallel non-crystalline relaxational springs based on the temperaturefrequency reduction rule and the VTF-type dielectric relaxation time. The findings revealed key information on the ratio of noncrystalline phases connected in series and parallel to the oriented crystalline phase.

Item Type: Article
Funders: Ministry of Education, Malaysia (Grant No. FRGS/1/2018/STG07/UM/02/6), Universiti Malaya (Grant No. ST001-2020)
Uncontrolled Keywords: Face-shear piezoelectricity; Piezoelectric relaxation; Resonance; Three-element model; Poly-L-lactic acid
Subjects: Q Science > QC Physics
Divisions: Faculty of Science > Department of Physics
Depositing User: Ms. Juhaida Abd Rahim
Date Deposited: 19 Oct 2023 08:26
Last Modified: 19 Oct 2023 08:26
URI: http://eprints.um.edu.my/id/eprint/41858

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