In an attempt to increase the Li+-ion diffusivity, poly(vinylidenefluoride-co-hexafluoropropylene)-(propylene carbonate+diethyl carbonate)-lithium perchlorate gel polymer electrolyte system has been irradiated with 70-MeV C5+-ion beam of nine different fluences. Swift heavy-ion irradiation shows enhancement in ionic conductivity at lower fluences and decrease in ionic conductivity at higher fluences with respect to unirradiated gel polymer electrolyte films. Maximum room-temperature (303K) ionic conductivity is found to be 2×10−2S∕cm after irradiation with a fluence of 1011ions∕cm2. This interesting result could be attributed to the fact that for a particular ion beam with a given energy, a higher fluence provides critical activation energy for cross linking and crystallization to occur, which results in the decrease in ionic conductivity. X-ray-diffraction results show decrease in the degree of crystallinity upon ion irradiation at low fluences (⩽1011ions∕cm2) and increase in crystallinity at higher fluences (>1011ions∕cm2). Analysis of Fourier-transform infrared spectroscopy results suggests the bond breaking at a fluence of 5×109ions∕cm2 and cross linking at a fluence of 1012ions∕cm2 and corroborate conductivity and x-ray-diffraction results. Scanning electron micrographs exhibit increased porosity of the polymer electrolyte after ion irradiation.
Integration of piezoelectric zinc oxide (ZnO) nanoparticles with SU8 in the form of photo-patternable nanocomposite films can lead to the development of a new generation of energy-harvesting microdevices. Design of such energy-harvesting micro/nano-systems will require knowledge of the mechanical properties of the SU8/ZnO nanocomposite thin films for various loadings of ZnO. This work presents characterization of mechanical properties of SU8/ZnO nanocomposite films with ZnO concentration varying in the range of 0–25 wt% via quasi-static and dynamic nanoindentation. These films were fabricated using conventional microfabrication steps involving dispersion of ZnO in SU8 by ultrasonication, followed by spin-coating and UV exposure. The elastic modulus obtained via quasi-static nanoindentation varies from ~6.2 GPa for pristine SU8 to ~8.8 GPa for SU8/25 wt% ZnO nanocomposite, while hardness varies from 402 MPa to ~520 MPa for SU8/ZnO nanocomposites in the same range of ZnO wt%. The experimentally-obtained elastic modulus has also been compared with estimates obtained via Eshelby–Mori–Tanaka micromechanics. Storage modulus, loss modulus and loss factor obtained via dynamic nanoindentation tests indicate that the SU8/ZnO nanocomposites exhibit viscoelastic behavior in the studied frequency-range of 10 Hz to 201.5 Hz. Microstructural characterization via scanning electron microscopy and optical characterization via UV–vis spectrometry of the nanocomposites have also been reported.
A nanogenerator is a nanodevice which converts ambient mechanical energy into electrical energy. A piezoelectric nanocomposite, composed of vertical arrays of piezoelectric zinc oxide (ZnO) nanowires, encapsulated in a compliant polymeric matrix, is one of most common configurations of a nanogenerator. Knowledge of the effective elastic, piezoelectric, and dielectric material properties of the piezoelectric nanocomposite is critical in the design of a nanogenerator. In this work, the effective material properties of a unidirectional, unimodal, continuous piezoelectric composite, consisting of SU8 photoresist as matrix and vertical array of ZnO nanowires as reinforcement, are systematically evaluated using finite element method (FEM). The FEM simulations were carried out on cubic representative volume elements (RVEs). Four different types of arrangements of ZnO nanowires and three sizes of RVEs have been considered. The volume fraction of ZnO nanowires is varied from 0 to a maximum of 0.7. Homogeneous displacement and electric potential are prescribed as boundary conditions. The material properties are evaluated as functions of reinforcement volume fraction. The values obtained through FEM simulations are compared with the results obtained via the Eshelby-MoriTanaka micromechanics. The results demonstrate the significant effects of ZnO arrangement, ZnO volume fraction, and size of RVE on the material properties.
Piezoelectric nanocomposites consisting of an orthotropic piezo-active polymer matrix and with piezo-ceramic nanoparticles as reinforcement are potential candidates as materials for structural components of the next-generation energyharvesting micro-devices that are compatible with flexible electronics. Prediction of effective electroelastic properties of such piezoelectric composites is an essential step towards design and development of such energy-harvesting micro/ nano-structures. This paper proposes a micromechanical model for determination of effective elastic, piezoelectric and dielectric properties of unidirectional piezoelectric polymer composites having spherical type inclusions embedded in an orthotropic matrix. The model is based on Mori-Tanaka's mean field homogenization scheme and involves the determination of piezoelectric Eshelby tensors. As an example, the effective electromechanical properties of PVDF (polyvinylidene fluoride)/PZT 7A (lead zirconate titanate) composite were determined using the micromechanical model and the results were validated with a finite element model and with experimental data available in literature. The results demonstrate that the micromechanics model developed here successfully predicts the effective electroelastic properties of piezoelectric orthotropic composite at low volume fractions of the reinforcement.
Present work designs and develops lead magnesium niobate-lead titanate (PMN-0.3PT) and polydimethylsiloxane (PDMS) based flexible piezoelectric-polymer composites for efficient mechanical energy harvesting through a combined experimental-theoretical approach. Solid-state reaction method was employed to synthesize PMN-0.3PT piezo-ceramic, which was subsequently used for the fabrication of vr-PMN-0.3PT/PDMS piezoelectric-polymer 0-3 composite with different volume fractions, vr = 0.03, 0.25, and 0.50 of PMN-0.3PT reinforcement. Uniformly distributed PMN-0.3PT particles were found to retain their structural symmetry across the volume fractions and are well adhered to the PDMS matrix. The- effective electromechanical properties of the composites were measured and compared with model predictions employing the finite element method and Eshelby-Mori-Tanaka (EMT) based micromechanical models. Considering that flexibility is a critical design parameter, we propose a new figure of-merit term- that would consider both electromechanical conversion as well as mechanical flexibility of the material. We show that vr = 0.5, PMN-0.3PT/PDMS 0-3 composite yields an optimum combination of energy harvesting performance and flexibility. Our study further demonstrates that the orientation of the PMN-0.3PT particles does not significantly influence the effective elastic and dielectric properties at low and moderate PMN-PT content, attributed to the lower aspect ratio of the reinforcement particles. The piezoelectric charge coefficient showed small yet finite change with increasing reinforcement content. A maximum current density, 35 nA/cm2, and electric field, 90 V/cm was obtained with cyclic compressive stress of 0.22 MPa (Force, 50 N) at 5 Hz, in a piezoelectric generator based on vr = 0.5.
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