Β-phase Poly Vinylidene Fluoride Research Articles

Controlling the polymorphs of PVDF membranes: Effects of a salt additive on PVDF polarization during phase separation processes

Polyvinylidene fluoride (PVDF) membranes, acclaimed for their outstanding chemical resistance, thermal stability, and mechanical properties, play a crucial role in diverse industrial purification applications. While various methods have been employed for fabricating PVDF membranes such as thermally induced, evaporation-induced, vapor-induced, and nonsolvent-induced phase separation processes, controlling the polarity of PVDF chains using these techniques remains challenging. Recent studies have shown that the nonpolar α-phase PVDF is susceptible to organic acid fouling owing to hydrophobic interactions, whereas the β-phase PVDF has demonstrated polarity and offers antifouling properties. Herein, porous PVDF membranes predominantly composed of the β-phase were successfully fabricated by incorporating a small amount of LiCl salt into the PVDF dope solution. The addition of LiCl influences ion–dipole moments between ions and PVDF during phase separation, simultaneously affecting the PVDF chain arrangement and membrane morphology. Since the LiCl additive alters both the pore size and structure of PVDF membranes, both freestanding and non-woven supported membranes were prepared and characterized to assess the effects of polarity and pore size on fouling tendency. Characterizations of prepared PVDF membranes revealed considerable changes in the PVDF polymorph, membrane morphology, pore size, and antifouling properties upon introducing the salt additive. Our findings imply that β-phase–dominant PVDF membranes can be effectively utilized in water purification applications.

A novel centrifugal electrospinning design for preparing of high alignment β-phase PVDF nanofibers for high-performance piezoelectric nanogenerators

The effects of polyvinylidene fluoride (PVDF) wt. % and electric fields on the production of PVDF fibers using a novel centrifugal electrospinning design were investigated. High-quality, bead-free fibers with diameter of (0.55 ± 0.04) μm were successfully produced. Fibers with exceptionally high β-phase content of 96.1 % and piezoelectric coefficient, d33 of (−157 ± 5) pC N−1 were obtained using PVDF amount and electric field of 14.0 wt % and 400 V cm−1, respectively. Under 3.0 N repetitive vertical forces, the fabricated piezoelectric nanogenerator (PENG) exhibited impressive open-circuit voltage, short-circuit current and power density of (32.6 ± 0.7) V, (3.26 ± 0.07) μA and (15.4 ± 0.6) μW cm⁻2, respectively. The production of high and well aligned β-phase in the fibers indicated by good d33 values are the likely reasons for the excellent performance of the PENG. Ultimately, potential of the fabricated PENG as a self-power supply for low-energy electronic devices was demonstrated.

Coordination-induced high-dielectric polymer coatings for high-energy-density lithium batteries

The full utilization of lithium ions through high-voltage operation is redeemed as one of the most promising ways to boost the energy density of the current lithium-ion batteries (LIBs). Nevertheless, the reliable operation of high-voltage LIBs is mainly inhabited by the detrimentally interfacial reactions on the cathode surface upon high charge voltages, which is closely correlated to the solvation structure of the electrolyte. In this work, we report a fluorine-carbon-oxygen (F-C-O) coordination-induced dielectric-enhancement strategy to manipulate the electrolyte solvation structure and thus improve the lithium utilization of cathode. To realize this, graphene oxide (GO) with abundant oxygenated groups is introduced to trigger the spontaneous formation of β-phase polyvinylidene fluoride (β-PVDF) with high dielectric constant coated on a polypropylene (PP) separator. The high-dielectric PVDF@GO/PP separator is endowed with the ability to manipulate the distribution and migration of ions, thus significantly improving the lithium-ion utilization rate of the cathode, maintaining the cathode robustness in the high-voltage cycling, leading to an appreciable improvement in the discharge capacity, rate performance, and cycling stability of LiNi0.8Co0.1Mn0.1O2 (NCM811)/Li cell at wide-temperature.

Asymmetrically Architectured PVDF Membranes with Enhanced Ion Conduction for Lithium-Metal Battery

BackgroundThe instability of lithium-electrolyte interface is the major challenge limiting the practical applications of Li-metal anode as well as Li-metal batteries. To stabilize the anode surface, an asymmetric polyvinylidene fluoride (PVDF) membrane consisted of a bi-continuously nanoporous dense layer and a packing of micro-sized spherulites is proposed. MethodsThe asymmetric PVDF membrane is served as the separator in lithium metal batteries, and the unique structure is prepared by nonsolvent induced phase separation (NIPS) method with triethyl phosphate as the solvent. Significant FindingsThe asymmetric PVDF separator presents an outstanding ionic conductivity of 1.92 mS cm−1 due to its high porosity and electrolyte uptake. Most significantly, the transference number of such separator reaches 0.73, which can be attributed to the enrich β-phase PVDF crystalline in the nanoporous dense layer. The battery performance in Li/LiFePO4 cells also exhibits a good capacity retention of 91% after 100 cycles at 0.5 C. Moreover, a remarkable rate capability with specific capacity of 92 mAh g−1 at 10 C is achieved, which is almost double of commercial polypropylene separator. These results demonstrate the promising potential for asymmetric PVDF membranes in lithium battery applications.

Stimuli-responsive piezoelectricity in electrospun polycaprolactone (PCL)/Polyvinylidene fluoride (PVDF) fibrous scaffolds for bone regeneration

Polymeric scaffolds are a determinant part of modern tissue engineering owing to their great diversity, adaptability, and processability. Interestingly, the physical properties of these scaffolds, e.g., porosity, mechanical properties, and biocompatibility, can be tuned to make them smart and stimuli-responsive. In this regard, piezoelectric materials can be applied to stimulate bone regeneration by converting mechanical impulses to electrical signals. In the present research, fibers made of various blend ratios of polyvinylidene fluoride (PVDF)/polycaprolactone (PCL) were fabricated, investigated and optimized to promote bone regeneration. Uniform fibers containing β-phase PVDF were obtained due to the simultaneous stretching and high voltage applied during electrospinning. Furthermore, components interaction, crystallinity, and piezoelectric behavior were estimated through fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and piezometery, respectively. The samples showed improved wettability and controlled biodegradability, and the piezoelectric charge output reached up to 7.5 pC/N in the sample containing 70 wt% PVDF. At the same time, these scaffolds could provide mechanical properties close to the native bone tissue relying on the PVDF component. In vitro assessments demonstrated that the composite scaffolds were biocompatible and could support cell attachment and proliferation. Moreover, their piezoelectric behavior promoted stem cell differentiation into osteoblasts. Considering the obtained results, the potential of piezoelectric PVDF/PCL blend fibers for bone scaffolds is indisputable.

Dielectric Spectroscopy of Ferroelectric Crossbred PVDF–TiO<sub>2</sub> Polymer Composite Thin Films

Polyvinylidene fluoride (PVDF) ferroelectric polymer blend with titanium dioxide (TiO2) is synthesized in the form of thin films by solution casting method. The synthesized PVDF-TiO2 composite films with a different wt% of TiO2 (2, 4, 6, 8, and 10) as fillers in the PVDF matrix were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and Fourier Transform Infrared (FTIR) spectroscopy. The XRD patterns of PVDF-TiO2 composite films confirmed the existence of a β-phase PVDF, uniform distribution of TiO2 particles in the polymer matrix and the crystallinity of the polymer composites was found to be enhanced. The SEM micrograph depicts the augmentation in the structural density due to the addition of TiO2 particles in the PVDF matrix. The dielectric constant of the PVDF-TiO2films is found to be an anomaly at lower frequencies and decreases with an increase in frequency agreeing with the Maxwell–Wagner type of interfacial polarization. The enhancement in the dielectric constant of PVDF-TiO2 composites at lower frequencies suggests that the prepared polymer composite thin films are useful as separator membranes in energy storage devices.

Characterization of a Biocomposite of Electrospun PVDF Membranes with Embedded BaTiO3 Micro- and Nanoparticles

Damage to bone tissue is a common health issue that tends to increase in severity with age and other underlying conditions. To take advantage of the piezoelectric effect on bone remodulation, piezoelectric materials can be used to fill patients bone defects. Polyvinylidene fluoride (PVDF) and barium titanate (BaTiO3) are both well-known polymeric and ceramic biomaterials, respectively, as well as piezoelectric at room temperature. To mimic the extracellular matrix, PVDF membranes were produced by electrospinning onto a rotating drum to promote the alignment of fibers and micro- and nano-sized tetragonal BaTiO3 particles were embedded into these membranes to try to enhance the piezoelectric response and, therefore, bioactivity. After defining the best deposition parameters to produce pure PVDF membranes, the same parameters were carried over for the embedded membranes and both were characterized, revealing that the proposed method for obtaining β-phase PVDF (the polymer phase with highest piezoelectric coefficient) through electrospinning is viable, producing fibers with coherent diameters and alignment. The presence of barium titanate conferred bioactivity to the membranes and caused a decrease in fibers’ diameter and in superficial charge density.

Unveiling the enhancement essence on Li2S deposition by the polarized topological β-polyvinylidene fluoride: Beyond built-in electric field effect

Electric field from ferroelectric materials was often applied to energy-storage devices to enhance their electrochemical reaction kinetics via the electrostatic interaction. However, traditional ferroelectric materials are difficult to be used commercially for their insulation. Herein, we elucidate a novel strategy to introduce the electrostatic interaction by polarizing the polyvinylidene fluoride (PVDF) binder used in the C/S cathodes for lithium-sulfur batteries. In particular, we show both experimentally and theoretically how an external electric field from β-phase PVDF induces unprecedented performance and stabilities. Density functional theory calculation results indicate that the polarized topological β-phase PVDF possesses not only an strong built-in electric field and an improved conductance that benefits both the deposition of LiPSs and the transport of Li+ ions, but also an enhanced adsorption capability to polysulfide ions. As a result, the specific capacity was improved by over 60 %, the rate capability (from 0.1 to 2.0 C) was enhanced by 138 %, and the capacity decay rate (1000 cycles at 1.0 C) largely decreases from 0.059 % to 0.038 % per cycle. Besides, the enhancement mechanism of Li2S deposition by electrostatic interaction has also been explored. This research would provide some new insight into the ferroelectric enhanced design of high-performance energy-storage devices.

A Biocompatible Self-Powered Piezoelectric Poly(vinyl alcohol)-Based Hydrogel for Diabetic Wound Repair.

Acute and chronic wounds, caused by trauma, tumors, diabetic foot ulcers, etc., are usually difficult to heal, while applying exogenous electrical stimulation to enhance the endogenous electric field in the wound has been proven to significantly accelerate wound healing. However, traditional electrical stimulation devices require an additional external power supply, making them poor in portability and comfort. In this work, a self-powered piezoelectric poly(vinyl alcohol) (PVA)/polyvinylidene fluoride (PVDF) composite hydrogel is constructed by establishing a distinctive preparation process of freezing/thawing-solvent replacement-annealing-swelling. The hydrogen bonding in the hydrogel is remarkably enhanced by the annealing-swelling process, which is stronger between PVA/PVDF molecules than that between PVA molecules, promoting transformation of the α-phase into the electroactive β-phase PVDF and facilitating formation of a much more crystalline structure with high cross-linking density. Hence, an obvious piezoelectric response with high piezoelectric coefficient and electrical signal output with superior stability and sensitivity and excellent mechanical strength and stretchability was achieved for hydrogels. PVA/PVDF composite hydrogels with good cytocompatibility significantly promote proliferation, migration, and secretion of extracellular matrix proteins and growth factors of fibroblasts, possibly through activating the AKT and ERK1/2 signaling pathways. In a wound model of diabetic rats, piezoelectric hydrogels could not only rapidly attract wound exudate and maintain the wet environment of the wound bed but also convert the mechanical energy generated by rats' physical activities into electrical energy, so as to provide local piezoelectric stimulation to the wound bed evenly and symmetrically in real time. Such an effect significantly promotes re-epithelialization and collagen deposition and increases angiogenesis and secretion of growth factors in wound tissue. Besides, it regulates the macrophage phenotype from the M1 subtype (pro-inflammatory subtype) to the M2 subtype (anti-inflammatory subtype) and reduces the expression levels of inflammatory factors, thus accelerating wound healing. The development of such a novel piezoelectric hydrogel provides new therapeutic strategies for chronic wound healing.

Solvent-assisted precipitation direct-write printing toward in-suit oriented β-phase polyvinylidene fluoride with tunable microarchitectures for energy harvesting and self-powered sensing

Additive manufacturing technology has attracted significant attention because it facilitates the one-step fabrication of complex structures for piezoelectric devices. In this study, a facile approach is proposed for manufacturing complex piezoelectric nanogenerators (PENGs) with an in-suit oriented β-phase of polyvinylidene fluoride (PVDF) based on solvent-assisted precipitation direct-write three-dimensional (3D) printing (SPDWP). This SPDWP has the ability to fabricate porous structures owing to the rapid nonsolvent-induced phase separation and controllable porosity of the fiber. In particular, the SPDWP based on ethanol precipitation increases the β-phase content of PVDF to 76.21%, representing a 1.5-fold improvement compared to that by the solvent casting technique. Moreover, the shape of the printed fiber—impacted by the printing parameters—significantly influences the piezoelectric performance. In particular, cylindrical fiber-based PENGs exhibit better piezoelectric performance than elliptical fiber-based PENGs, producing a higher voltage output of 11.3 V owing to the structural deformation, as confirmed by the simulation results. As expected, these printed PENGs can detect a variety of human movements, demonstrating that SPDWP is a novel method for fabricating 3D structural PENGs for self-powering microelectronic applications with the advantages of achieving geometric complexity, manufacturing simplicity, and low cost.

Investigation on Crystal-Structure, Thermal and Electrical Properties of PVDF Nanocomposites with Cobalt Oxide and Functionalized Multi-Wall-Carbon-Nanotubes.

Nanocomposites of polyvinylidene fluoride (PVDF) with dimensional (1D) cobalt oxide (Co3O4) and f-MWCNTs were prepared successfully by the solution casting method. The impact of 1D Co3O4 filler and 1D Co3O4/f-MWCNTs co-fillers on the structural, thermal, and electrical behavior of PVDF were studied. The crystal structural properties of pure PVDF and its nanocomposite films were studied by XRD, which revealed a significant enhancement of β-phase PVDF in the resulting nanocomposite films. The increase in β-phase was further revealed by the FTIR spectroscopic analysis of the samples. TG, DTA, and DSC analyses confirmed an increase in thermal stability of PVDF with the addition of nano-fillers as well as their increasing wt.%. From impedance spectroscopic studies, it was found that the DC conductivity of PVDF increases insignificantly initially (up to 0.1 wt.% of nano-fillers addition), but a significant improvement in DC conductivity was found at higher concentrations of the nano-fillers. Furthermore, it was observed that the DC conductivity decreases with frequency. The increase in DC conductivity corresponded to the strong interactions of nano-fillers with PVDF polymer chains.

Effects of biomimetic cross-sectional morphology on the piezoelectric properties of BaTiO3 nanorods-contained PVDF fibers

In this study, the effects of the morphology of components on the performance of a piezoelectric nanogenerator were investigated. Polyvinylidene fluoride (PVDF) fibers with biomimetic cross-sectional morphologies inspired by plants were fabricated by integrating melt spinning, winding, and corona poling. The cross-sectional morphology of the PVDF fiber significantly influenced the piezoelectric performance because of differences in the exterior surface area and contact volume, which are important in the production of β-phase PVDF and crystallinity. The daffodil flower-shaped PVDF fiber exhibited the best piezoelectric performance among the PVDF fibers with various biomimetic cross-sectional morphologies (i.e., daffodil flower, radish flower, papyrus stem, and stalk grain stem) possessing different active areas for piezoelectricity generation. Its open-circuit voltage of 36.05 V and short-circuit current of 3.126 μA are attributable to its highest exterior surface area and contact volume, which maximize the active area (deformation area) for piezoelectricity generation. The effect of the morphology (nanoparticles and nanorods) of BaTiO3, which is another component of the piezoelectric nanogenerator, was also investigated using BaTiO3-contained PVDF fibers involving the daffodil flower-like cross-sectional morphology, namely, the PVDF-daffodil/BaTiO3 nanoparticle (NP) and PVDF-daffodil/BaTiO3 nanorod (NR). Compared with nanoparticles, the rod morphology more efficiently promoted asymmetry in the fiber during fabrication. The PVDF-daffodil/BaTiO3 NR produced an excellent open-circuit voltage of 62 V and a maximum power of 91 μW from human motion. This study provides new insights for the practical mass production and utilization of high-performance piezoelectric nanogenerators.

Probing the effect of graphene surface chemistry on compatibility, crystallinity, and viscoelastic response of polylactic acid/polyvinylidene fluoride blends

Polylactic acid (PLA)/polyvinylidene fluoride (PVDF)/graphene nanocomposites were prepared by solution casting technique to study the effect of graphene surface chemistry on blend compatibility. Surface and cross-sectional morphology and atomic force microscopy analyses revealed that the addition of hydrophobic graphene resulted in the highest level of compatibility in PLA/PVDF blends. The untreated graphene exhibited a more compatibilizing effect than the hydrophilic graphene. According to X-ray diffraction (XRD) results, the crystallinity of polymers was enhanced in the presence of graphene for the compatibilized blends through the interfacial assisted nucleation mechanism. The formation of β-phase PVDF crystals was also increased in the presence of PLA and graphene, especially for the blend loaded with hydrophobic functionalization. Based on XRD and rheological results, the order of graphene dispersion quality was as follows: hydrophobic> untreated>hydrophilic. The improved dispersion quality of graphene nanoplatelets, along with the higher interfacial modulus for the compatibilized blends, were found responsible for the observed enhancement in the elasticity of the samples. The current study demonstrated the promising potential of graphene nanoplatelets with hydrophobic functionalization in compatibilizing the immiscible PLA/PVDF blends. Moreover, the enhanced β-phase crystals of PVDF and increased PLA crystallinity are highly useful in advanced applications that require piezoelectricity and biocompatibility.

Characterization of β-PVDF-based nanogenerators along with Fe2O3 NPs for piezoelectric energy harvesting

β-phase polyvinylidene fluoride (PVDF) nanogenerators along with various concentrations (0.2, 0.4, 0.6, and 0.8 wt%) of iron oxide (Fe2O3) nanoparticles were produced using the electrospinning technique. The characterization of the free- and doped-nanogenerators was examined by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and 57Fe Mossbauer spectroscopy, dielectric measurements, and piezoelectric effect analysis. All the analyses demonstrated that the structural transition in the specimens at doping ratios are above the critical concentration of 0.4% by wt. of Fe2O3 NPs in PVDF, superparamagnetic behavior of the iron oxide particles in the composite. Utilization of the β-PVDF along with Fe2O3 NPs (0.4 wt%) exhibited higher piezoelectric properties with respect to the free form and the other additive concentrations. Considering the piezoelectric properties of the nanogenerator, the output voltage of the β-PVDF in the presence of the 0.4 wt% of Fe2O3 NPs reaches up to 1.39 V by increasing the peak amplitude to almost 50% while the undoped β-PVDF nanogenerator reveals almost to 0.93 V at the same impact frequency (6–7 Hz).

Enhancing combustion performance of nano-Al/PVDF composites with β-PVDF

Solid energetic nanocomposites, consisting of reactive metal particles and oxidizers, find broad applications ranging from pyrotechnics to solid rocket propellants and solid ramjet fuels. In particular, nano-aluminum (n-Al) and polyvinylidene fluoride (PVDF) are attractive fuel and oxidizer materials, due to the high energy density of n-Al, and the high oxidizing potential and excellent mechanical properties of PVDF. PVDF is a semi-crystalline polymer and has three common crystalline phases, alpha (α), gamma (γ), and beta (β) phases. Many research works have focused on the chemical reactions between Al and PVDF, yet the effect of PVDF crystallinity on the Al/PVDF reaction is unknown. Here, we experimentally and computationally demonstrate that increasing the mass fraction of β-phase PVDF from 2.5 to 25% in Al/PVDF composites substantially improves peak pressure by 90% (from ~34 to ~64 psi) and pressure rise rates by 300% (from 2.5 psi/ms to 10 psi/ms). This stems from the alignment of F atoms along one side of the β-PVDF polymer chain, making it structurally conducive to reacting with Al particles to form strong Al-F interactions. This strong interaction leads to higher binding energy between, and hence higher reactivity in, β-PVDF and Al. Our research provides a new method for enhancing the reactive performance of Al/PVDF composites by increasing the content of β-PVDF.

Piezoelectric PVDF membranes for use in anaerobic membrane bioreactor (AnMBR) and their antifouling performance

Membrane fouling is a common phenomenon in anaerobic membrane bioreactor (AnMBR), deteriorating membrane performance and increasing the operation costs of AnMBR. In this study, β-phase polyvinylidene fluoride (PVDF) flat sheet membranes were successfully prepared by first mixing PVDF powder with ionic liquid [BMIM]PF6 and subsequently casting them using thermally induced phase separation (TIPS), followed by high voltage polarization treatment to endow the PVDF membranes with piezoelectric properties. For the first time in AnMBR, we reported in this study on the piezoelectric PVDF membrane that generates in-situ vibrations to reduce membrane fouling by applying a given frequency and alternating voltage (AV). The results suggested that the steady-state water flux through the piezoelectric membrane in AnMBR operation increased along with the AV, enhancing it by up to 72.6% (at 20 V) compared to that of the membrane without applying AV. In addition, high water flux was obtained at the optimal operating frequency of 10 kHz when the cross-flow mode was taken into consideration in AnMBR operation in this study, although the resonance frequency with maximum amplitude of the membrane was 600 kHz. These results indicate that the piezoelectric β-PVDF membrane is effective at minimizing or alleviating the membrane fouling when the electric field simultaneously applied during AnMBR operation. During the 30-day operation of AnMBR with the β-PVDF membrane with poling, the COD removal rate was maintained at over 90%, even if the applied frequencies and voltages were changed during the operation.

Ablation of piezoelectric polyvinylidene fluoride with a 193 nm excimer laser.

The unique flexible and piezoelectric properties of polyvinylidene fluoride (PVDF) films would allow for new applications for integrated bioelectronic devices. The use of these films has been precluded by the difficulty in machining them into small, discrete features without damaging the properties of the material. The etching of piezoelectric PVDF by means of a 193 nm excimer laser is explored and characterized. Etch rates are shown for common laser fluence values, along with images of the quality of the cuts to provide the reader with an understanding of the compromise between etch rate and edge roughness. The authors describe a novel method for the etching of piezoelectric, -phase PVDF. While PVDF is flexible, acoustically matched to biological tissue, and has a wide resonance bandwidth, it is often overlooked as a piezoelectric material for micro-electrical-mechanical-system devices because of the difficulty in fabrication. In this paper, the authors characterize the etch rate and quality while using a 193 nm argon fluoride excimer laser for patterning.

Hydrogen-bond induced nucleation and growth of β-poly(vinylidene fluoride)

A series of polyvinylidene fluoride (PVDF)/layered double hydroxide (LDH) composite membranes were prepared via phase inversion method, in which the presence of LDH promotes the formation of β-phase PVDF. This work reveals the key role of hydrogen-bonds on the nucleation mechanism and crystallization behavior of PVDF. The composite membranes exhibit improved porosity and hydrophilicity, leading to an enhanced antifouling property against proteins.

An electroactive β-phase polyvinylidene fluoride as gel polymer electrolyte for magnesium–ion battery application

The gel polymer electrolytes (GPEs) are currently interesting research area in rechargeable batteries. In the present study, synthesis and characterization of electroactive gel polymer electrolyte (EGPE) for Mg-ion batteries application have been investigated. The bead free electroactive polyvinylidene fluoride (PVDF) with high porosity is achieved by an electrospinning process. The β-phase of PVDF is polar and electroactive with a high dipole moment. Electroactive β-phase is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscopy (FESEM) study is done to analyze the structure and morphology of the electroactive membrane. The electroactive gel polymer electrolyte is formed by immersing an electroactive PVDF membrane in 0.3 M magnesium perchlorate (MgClO4) and propylene carbonate (PC) solution. The ionic conductivity of electroactive β-phase PVDF membrane is achieved to be 1.49 mS cm−1 at 30 °C, which is higher than commercial available polypropylene (PP) Celgard. Tortuosity of electroactive gel polymer electrolyte is found to be 1.44. The voltage stability of the EGPE is stable up to a high voltage of 5.0 V against Mg+2/Mg. The total ionic transference number and magnesium ion transference number of EGPE are also investigated to confirm high ionic conductivity.

A self-cleaning piezoelectric PVDF membrane system for filtration of kaolin suspension

Exploring innovative membrane material is an important approach to mitigate membrane fouling. This study investigated a self-cleaning polyvinylidene fluoride (PVDF) piezoelectric membrane system which can vibrate at controlled frequencies, amplitudes and waveforms to mitigate membrane fouling. Among different PVDF films, the one of the highest content of β-phase PVDF was selected because of the greatest piezoelectric coefficient. The film was pin punched to 0.14 ± 0.02 mm holes for filtration purpose. The characteristic peaks of vibration velocity and amplitude were identified by measurements of a Scanning Laser-Doppler vibrometer with tiered driving voltages. The piezoelectric membrane was tested in a dead-end filtration system fed with 0.5 g L−1 kaolin suspension of 907.7 nm Z-average diameter at a constant filtration pressure of 34.5 kPa. The results indicate vibration velocity is more important than amplitude to choose the vibration frequency in order to optimize membrane fouling control. The piezoelectric membrane with continued vibration driven by 24 V (peak-to-peak) and sine wave at the frequency of 1601 Hz (the peak of vibration velocity) yielded 87 ± 3% higher permeate flux than control test, compared to 30 ± 3% increase at the frequency of 664 Hz (the peak of vibration amplitude). However, the antifouling effect was not apparent with intermittent vibration, possibly due to interrupted processes of cleaning and fouling prevention. The mechanistic explanation of cleaning suggests lift force brought by hydraulic shearing is more important than inertial lift force of vibration.