• Polymer(Korea)
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• v.35 no.2
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• pp.130-135
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• 2011

Along with the fast development of electronics, the demands of portable electronics and wireless sensors are growing rapidly. The need for self-powering materials capable of powering the electrical devices attached to them is increasing, The piezoelectric effect of polyvinylidene fluoride (PVDF) can be used for this purpose. PVDF has a special crystal structure consisting of a ${\beta}$-phase that can produce piezoelectricity. In this paper, multilayer PVDF films were fabricated to increase the ${\beta}$-phase content. A solution of 10% concentration N;N-dimethylacetamide (DMAc) in PVDF (PVDF/DMAc) was used to fabricate the films via spin coating technique with the following optimum process parameters: a spin rate of 850 rpm, spin time of 60 s, drying temperature of $60^{\circ}C$, and drying time of 30 min, Compared with single-layer PVDF films, the multilayer films exhibited higher ${\beta}$-phase content. The ${\beta}$-phase content of the films increased gradually with increasing number of layers until 4, Maximum ratio of ${\beta}$-phase content was 7.72.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.11
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• pp.712-715
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• 2016

In this paper, we fabricated flexible CNT/PVDF piezoelectric composite device by introducing CNTs (carbon nanotubes) into PVDF (poly-vinylidene fluoride) solution using spray coating technique. Flexible PEDOT:PSS conducting polymer was used as electrodes. We tried to improve the piezoelectric performance from the CNT/PVDF composite film by increasing the portion of the ${\beta}$-phase PVDF in the film. We confirmed the structural conformation of the CNT/PVDF composite film as a function of CNT concentration by using FT-IR (fourier transform infra-red). As increasing CNT concentration, portion of the ${\beta}$-phase PVDF and resulting piezoelectric performance increased in the CNT/PVDF composite film. We found that CNTs introduced were played as seeds for formation of the ${\beta}$-phase PVDF in the CNT/PVDF composite film and resulting improvement of the piezoelectric performance.

• Composites Research
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• v.26 no.2
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• pp.123-128
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• 2013

The PVDF (polyvinylidene fluoride) fibers were prepared using the wet spinning processing. To improve ${\beta}$-phase crystalline which closely related piezoelectric property PVDF wet spun fibers conducted post treatment. Post treatment is consisted of heat stretching and annealing process. The heat stretching and annealing conditions were controlled by changing temperature between glass transition temperature and melting temperature. From these experimental data, the resulting crystal structure of the ${\beta}$-phase crystalline was confirmed by FT-IR and XRD experiments. From these analysis results, optimum stretching and annealing conditions of the wet spun PVDF fibers were founded to increase high ${\beta}$-phase crystalline. Furthermore results showed that thermal processing had a direct effect on modifying the crystalline microstructure and also confirmed that heat stretching and annealing could increase the degree of crystallinity and ${\beta}$-phase crystalline. Finally, piezoelectric constant ($d_{11}$) of the post heat treated PVDF fibers reinforced composite were measured to investigate the feasibility for the sensing materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.7
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• pp.550-554
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.256-256
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process. Charge accumulation and resulting electric field generation mechanism by spray coating method were shown in Fig. 1. The capacitance of the CNT/PVDF films increased by adding CNTs into the PVDF matrix, and finally saturated. However, the I-V curves didn't show any saturation effect in the CNT concentration range of 0~4 wt%. Therefore we can control the performance of the devices fabricated from the CNT/PVDF composite film by adjusting the current level resulted from the CNT concentration with the uniform capacitance value.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.8
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• pp.565-571
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• 2003

We prepare the PVDF thin film using vacuum deposition method with the application of voltage and obtain the optimum deposition condition for $\beta$-PVDF thin film on the basis of the results of FT-IR, crystallinity of $\beta$ phase, surface roughness studies with varying the condition. The phase of PVDF thin film is analyzed by the FT-IR spectrum. When the substrate temperature and applied voltage increase from 3$0^{\circ}C$ to 9$0^{\circ}C$ and from 0kV to 9kV, respectively, the crystallinity of $\beta$ phase is introduced as large as 64%. It means that the substrate temperature and applied voltage allow the phase transition of $\beta$ phase to occur more easily. Also, the surface roughness of PVDF thin film decreases from 65.1nm to 36.6nm with the increase of substrate temperature. In results, we obtain the optimum deposition conditions for $\beta$-PVDF thin film from these experimental results and measure the Properties of the $\beta$-PVDF film deposited in the optimum condition. The dielectric properties such as dielectric constant and loss tangent decrease from 2.34 to 0.44 and from 0.27 to 0.04 with the increase of frequency, respectively.

• Polymer(Korea)
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• v.35 no.6
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• pp.605-609
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• 2011

Composite nanofibers were prepared by electrospinning and thermal treatment from poly (vinylidene fluoride) (PVDF)-$SiO_2$ blend solution. The nanofibers were stacked on layers to produce fully interconnected pores. TEM micrographs and EDX spectra confirmed the presence of $SiO_2$ in the composite nanofibers. The porosity of nanofibers was effectively enhanced by the introduction of electrospinning technique. ATR-FTIR and XRD results revealed that PVDF in the composite nanofibers exhibited the mixture crystal structure of ${\alpha}$-phase and ${\beta}$-phase. The crystal structure of ${\alpha}$-phase and crystallinity increased by the thermal treatment. In addition, the mechanical properties, thermal stability and hydrophobicity were markedly amplified by the thermal treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.2
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• pp.94-97
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• 2018

Lead zirconate titanate/poly-vinylidene fluoride (PZT/PVDF) piezoelectric devices were fabricated by incorporating carbon nanotubes (CNTs), for use as flexible energy harvesting devices. CNTs were added to maximize the formation of the ${\beta}$ phase of PVDF to enhance the piezoelectricity of the devices. The phase transition of PVDF induced by the addition of CNTs was confirmed by analyzing the X-ray diffraction patterns, scanning electron microscopy images, and atomic force microscopy images. The enhanced output efficiency of the PZT/PVDF piezoelectric devices was confirmed by measuring the output current and voltage of the fabricated devices. The maximum output current and voltage of the PZT/PVDF piezoelectric devices was 200 nA and 350 mV, respectively, upon incorporation of 0.06 wt% CNTs.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.1-8
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• 2018

The 23 wt% polyvinylidene fluoride (PVDF)/15 wt% polyurethane (PU) fibers were electrospun using the conjugated nozzle at a flow rate of 1.0 mL/h and an electric field of 1 kV/cm. The formation of ${\beta}$ crystal phase in the PVDF and the PVDF/PU fibers was confirmed by Fourier transform infrared spectroscopy. After electrospinning, the asspun fibers were immersed in a boiling water and then dried at $100^{\circ}C$ in a convection oven to make a crimp phenomenon. The crimps with a diameter of $2.0{\pm}0.08{\mu}m$ were observed for the PVDF/PU fibers after hydrothermal treatment without sacrificing the extent of ${\beta}$ crystal phase. All the PU, PVDF and PVDF/PU fibers exhibited average cell viability of more than 98 %. The cell proliferation results suggested that L-929 cells adhered well to the PU, PVDF and PVDF/PU fibers and proliferated continuously with increasing time, indicating that the PVDF/PU fibers are highly applicable to the biomedical applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.3
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• pp.221-228
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• 1998

In this study, the $\beta$-Polyvinylidene fluoride(PVDF) thin films were fabricated by physical vapor deposition method. Also, the properties of dielectric relaxation were studied to understand carrier's behavior of PVDF thin films, to be regarded as the excellent piezo and pyroelectricity. In the process of vapor deposition, the $\beta$-PVDF thin films have been fabricated under the condition of the substrate temperature at 3$0^{\circ}C$, the applied electric field at 142.8kV/cm and the pressure at 2.0${\times}10^{-5}$torr. The dielectric properties of PVDF have been studied in the frequency range 10Hz to 1MHz at temperature from 30 to $100^{\circ}C$. The relative dielectric constant of $\alpha$ and $\beta$-PVDF were 6.8 and 9.8, respectively, under a frequency of 1kHz. Such a phenomenon was caused by the decrease in intermolecular forces originated by the phase-transition from the TGTG' molecular conformation to the TT planar zig-zag conformation. And the relative dielectric constant is increased as a measuring temperature increases, because of the reduction of relaxation time caused by the decrease of intermolecular force.