Papers by Keyword: Polyvinylidene Fluoride (PVDF)

Abstract: Advanced biocompatible piezoelectric composites have gained significant attention for the development of flexible medical devices and especially related to materials structures that mimic the natural tissue structures. Natural piezoelectricity within the human tissues is reviewed, together with nature-based piezoelectric materials, their advantages and potential for designing the structures for biomedical applications. Electrospun Polyvinylidene fluoride (PVDF) nanofiber matrix, reinforced with silver nanoparticles (AgNPs) is discussed, including specific applications in bone grafts, biosensors and energy harvesting. Processing parameters of the electrospinning fabrication technology have a strong influence on the composite piezoelectricity. Computational models of piezoelectric composites have become a major support in material design for the real case applications. Existing approaches to the numerical modeling of piezoelectric composites have been shortly reviewed toward a recent trend of AI supported modeling for providing effective composite properties, prediction and optimization of material properties and behavior, such as the output voltage and power. Polymer-based biomedical piezoelectric composites have shown excellent results in laboratory research from aspects of their flexibility and possibility to tailor their electro-mechanical properties. However, output piezoelectric signals are still much lower than in the case of traditional ceramic-based materials, including challenges related to the stability of the electric signal, signal noise, piezoelectric impedance and durability of composites with nature-based reinforcements. Future directions in custom composite design, including currently available computational models to enable more rapid development of biomedical piezoelectrics are elaborated at the end.

Abstract: Polyvinylidene fluoride (PVDF)/PEG-POSS hybrid membrane was prepared by immersion phase separation process. The hybrid membranes were characterized by pure water flux, retention ratio to BSA, contact angle, shrinkage ratio and scanning electron microscopy (SEM). The hydrophilicity of the membrane was improved. The contact angles decreases from 82.2°to 76.3°. The shrinkage ratio decreases and the pure water flux increased when 1.0% POSS was used. Keywords: polyvinylidene fluoride (PVDF); PEG-POSS; hybrid membrane; hydrophilicity

Abstract: Poly (vinylidene fluoride) membranes were prepared from the ternary mixture of PVDF/ 1, 2 - propylene glycol/dimethylacetamidevianon-solvent induced phase separation (NIPS). The effect of the addition of the 1, 2 - propylene glycol content, the Coagulation Bath Temperature and the concentration of PVDF on the performance and structure of the PVDF membranes was studied in the present investigation.The results showed that with increasing polymer concentration, the mechanical strength increased,and the structure of membrane changed from finger-like macro-voids structureto sponge-like structure.It was found that water flux, breaking elongation and tensile strength of the membrane increased with increasing 1, 2 - propylene glycol content, when the content reached 41wt.%, the water flux reaches a maximum.The morphology of PVDF can be improved by the addition of 1, 2 - propylene glycol, which was changed from finger-like structure to sponge-like structure. And the dense skin layer of PVDF membranes became thicker with increasing 1, 2 – propyleneglycol. The tensile strength decreasedfrom 3.3 to 2.1MPa, breaking elongation decreased from 315% to 280% andthe pure water flux increased from 91 to 909 L·m^-2·h^-1. as the coagulation bath temperature (CBT) decreased from 30°C to 5°C.With this condition, the sponge-like hollow fiber membrane hassuccessfully spun.

Abstract: The 2-thiol benzothiazole was blended in Polyvinylidene fluoride (PVDF) membrane to prepare a kind of PVDF modified ultrafiltration membrane that could be used to remove mercury ion in water treatment. The water flux and retention rate of BSA of obtained PVDF modified ultrafiltration membrane was 222 L/m²·h and 92.33% respectively. The membrane performance were characterized by infrared spectroscopy (FT-IR) and water contact angle measurement. The results showed that, the PVDF modified membrane presented better adsorption ability for mercury ion than the traditional PVDF membrane. After 4 phases of adsorption/desorption, the modified membrane maintained a mercury ion adsorption amount of 0.264 mg/cm² and the desorption rate could reached 94%.

Abstract: The leakage and fatigue characteristics of polyvinylidene fluoride (PVDF) are investigated for flexible electronics. The crystallization, frequency responses, leakage currents, current-voltage characteristics, and fatigue characteristics of PVDF film are measured using X-ray diffraction and an electrometer. Results show that a PVDF model with a resistive load exhibits high-pass filter characteristics. The frequency band of PVDF film increases with increasing resistive load and capacitance. The break frequencies for 100 kΩ, 300 kΩ, 700 kΩ, and 1 MΩ at the break frequency are 611, 207, 88, and 61 Hz, respectively. The hysteresis area of ΔH slightly increases with increasing input voltage. The leakage current of PVDF film is higher for a lower delay time under a given applied electric field. The average leakage currents for delay times of 10 and 1000 ms are 0.565 and 73.8 pA, respectively. The magnitude of the current values increases with decreasing delay time at a given drive voltage. PVDF film induced larger degradation when the number of stress cycles was increased to about 105 cumulative cycles.

Abstract: A proton exchange membrane, poly (vinylidene fluoride)(PVDF) blended polystyrene sulfonated acid(PSSA) was prepared by Blend polymerization method. Mechanical properties of membranes were investigated by the multi-functional material experiment machine.The influences of the content of the styrene on the proton conductivity and methanol permeability of the membranes were studied by the impedance analyzer and gas chromatography instrument. The results showed that Polystyrene is easily blended into PVDF and mechanical properties were improved, with increasing of the content of styrene, the proton conductivity of PVDF-PSSA membranes was increased, and arrived at maximum as the styrene content was 20%, correspondingly, methanol permeability became large gradually.

Abstract: A proton exchange membrane, poly (vinylidene fluoride) blended polystyrene sulfonated acid (PVDF-PSSA) was prepared. Fourier transform infrared spectroscopy is used to characterize changes of the membrane's microstructures after grafting and sulfonation. The morphology of the membrane's microstructures and distribution of sulfur on the cross section after grafting and sulfonation is studied by scanning electrolytic microscope. The results showed that polystyrene is easily blended into PVDF. The sulfonation reaction occurred not only on the surface of the membrane, but also in the membrane.

Abstract: Randomly orientated electrospun poly(vinylidene fluoride) nanofiber membranes were directly used as active layers to make mechanical-to-electrical energy conversion devices. Without any extra poling treatment, the device can generate high electrical outputs upon receiving a mechanical impact. The device also showed long-term working stability and ability to drive electronic devices. Such a nanofiber membrane device may serve as a simple but efficient energy source for self-powered electronics.

Abstract: Polymethylmethacrylate (PMMA) modified poly(vinylidene fluoride) (PVDF) hollow fiber ultrafiltration membranes were prepared by wet spinning method using polyvinylpyrrolidone (PVP) as pore-foaming agent and mixture of dimethyl formamide (DMF)/methyl ethyl ketone (MEK) as solvent. The effects of PVDF, PMMA, PVP, and solvent ratios in the spinning solution on the permeation properties of the formed membranes were studied. The results showed that the performance of the membrane is the best with a pure water flux of 117 L/m2•h and rejection rate of 82% to bovine serum albumin (BSA), when the concentrations of PVDF, PMMA, PVP, DMF and MEK are 17, 3, 3, 60 and 17 wt%, respectively.

Abstract: The main goal of this research is studying the crystal structure and formation of both free radicals and trapped space charges in the pure and doped polyvinylidene fluoride (PVDF) films with various concentrations of transition metal halides TMHs (AlCl₃, ZnCl₂, and CoCl₂). Electron Spin Resonance (ESR) was used to detect the existence of free radicals and the probable magnetic interactions between the halide and PVDF. The hyperfine splitting of the ESR was used to study the electronic structure of the existence radicals. Thermally stimulated dielectric response measurements have been made using Frequency Resolved Dielectric Spectroscopy (FRDS). This was useful for studying the formation and trapping of the space charge to enhance the results obtained by ESR. The new crystalline structures and the complex compounds which may be developed due to the chemical reaction between the polymer and the added halides were analysid.