Fabrication and Characterization of a Flexible PVDF Fiber-based Polymer Composite for High-performance Energy Harvesting Devices

Abstract

A flexible polyvinylidene fluoride (PVDF)/polydimethylsiloxane (PDMS) composite prototype with high piezoelectricity and force sensitivity was constructed, and its huge potential for applications such as biomechanical energy harvesting, self-powered health monitoring system, and pressure sensors was proved. The crystallization, piezoelectric, and electrical properties of the composites were characterized using an X-ray diffraction (XRD) experiment and customized experimental setups. The composite can sustain up to 100% strain, which is a huge improvement over monolithic PVDF fibers and other PVDF-based composites in the literature. The Young's modulus is 1.64 MPa, which is closely matched with the flexibility of the human skin, and shows the possibility for integrating PVDF/PDMS composites into wearable devices and implantable medical devices. The $300{\mu}m$ thick composite has a 14% volume fraction of PVDF fibers and produces high piezoelectricity with piezoelectric charge constants $d_{31}=19pC/N$ and $d_{33}=34pC/N$, and piezoelectric voltage constants $g_{31}=33.9mV/N$ and $g_{33}=61.2mV/N$. Under a 10 Hz actuation, the output voltage was measured at 190 mVpp, which is the largest output signal generated from a PVDF fiber-based prototype.

Fig. 1. Fabrication procedure for uniaxial PVDF fiber/PDMS compsite

Fig. 2. Simulation of electric potential distribution on the EpCA ES setup

Fig. 3. SEM of electrospun PVDF fibers.

Fig. 4. The measurement system of (a) d₃₁ value and (b) d₃₃ value

Fig. 5. The relative impact of different parameters in the case of targeting to (a) (b) (c) fiber diameter and (d) fiber alignment level.

Fig. 6. The SEM micrograph of PVDF fibers fabricated under optimum conditions

Fig. 7. Stress-strain curve of the three PVDF/PDMS composite samples

Fig. 8. X-ray diffraction spectrum of PVDF fibers. The spectrum reveals a high percentage of β-phase at a peak of 20.8°.

Fig. 9. The measurement data of piezoelectric charge and piezoelectric voltage constant

Fig. 10. Voltages generated under the same pressure in the axial loading direction at different frequencies: 10 Hz, 20 Hz, 40 Hz, and 60 Hz.

Table 1. Implementation procedure for applying Taguchi’s method

Table 2. Design of Experiment and results for the fiber diameter

Table 3. Design of Experiment and results as the Quality character is fiber alignment

Table 4. Summary of reports on PVDF-based composite and PVDF monolithic fibers. NFES: Near-field Electrospinning, FFES: Far-field Electrospinning, CNT: Carbon Nanotube, N/A: Not available