Vinylidine Fluoride Research Articles

Surface modification of grafted porous polyvinylidine fluoride membrane with graphene oxide for vanadium redox flow battery

Abstract Vanadium Redox Flow Battery (VRFB) is an energy storage flow battery in whichthe key material for VRFB is the membrane that determines the cost and performance of the battery. Porous membranes have shown a great potential as a membrane due to their high stability, cheap and high selectivity. Poly(vinylidine fluoride) (PVDF) is a type of porous membrane that was extensively studied as a potential material for surface modification due to its thermal and chemical stability, inexpensive and mechanical properties. This study aims to develop a highly selective, high-performance modified PVDF membrane using surface grafting and functionalization for VRFB application using the sonication method. Graphene oxide (GO) is a trending material in the field due to its excellent properties such as being highly resistant to alkaline/acidic and strong mechanical strength, low cost and easily accessible. In this work, GO was functionalized on both sides of grafted PVDF using the sonication technique. Hydrogen bond from modification with GO caused the membrane to be a hydrophilic and FTIR results proved that new peaks appeared which relates to carbon bond from GO. Proton conductivity of modified membrane is recorded higher than commercial VRFB membrane, Nafion.

Gel Electrolytes for Lithium-Ion Batteries: An In-Situ Approach

Gel electrolytes are a recurrent topic in the lithium-ion battery community, and are of interest because they bridge the materials gap between solid ion conductors like polymers and ceramics and liquid electrolytes. A wide variety of engineering polymers have found use as gel or gel-like electrolyte components in lithium-ion batteries, including poly(vinylidine fluoride), poly(ethylene oxide), and poly(acrylonitrile). In theory, a gel electrolyte should allow the electrolyte to have solid-like mechanical properties while retaining liquid-like ion transport and passivation properties. But does this compromise really occur? What are the trade-offs? This talk will explore the topic of gel electrolytes for lithium-ion batteries by examining several examples synthesized through in-situ polymerization of the 3D network within the liquid electrolyte using both radical and cationic polymerization methods. In-situ polymerization occurs in both organic and aqueous systems, allowing for a broad comparison of electrolyte types for a wide range of lithium-ion battery types, including the growing family of aqueous lithium ion batteries. Figure 1

AC/DC Magnetic Field Sensing Utilizing Mechanically Mediated Product Effect of Ampere Force Caused by Eddy Currents and Piezoelectricity in a Magnetoelectric Disk

The last two decades have witnessed an ever‐increasing research effort devoted to the development and application of magnetoelectric (ME) sensing composites. Herein, the ME effect in a metallic/polymeric composite fabricated by adhering silver electrodes to two surfaces of one poly(vinylidine fluoride) (PVDF) disk is explored. To obtain obvious ME response, the resonance frequency of the experimental setup is measured. Furthermore, it is proved that the ME coupling in the composite (silver/PVDF/silver) originates from the product effect of the piezoelectric effect and ampere force produced by eddy currents under DC bias magnetic fields. By observing measurement results, the ME voltage is approximately considered to be proportional to both AC and DC magnetic fields. Consequently, the average ME voltage coefficient is obtained as 384.73 mV cm−1 Oe at a DC magnetic field value of 1000 Oe. Considering the magnetic fields and eddy current, a theoretical model of ME coupling is developed by combining the ampere force expression and piezoelectric equations, which matches well with measurement results. Without the need of magnetic phase and an external power supply, the proposed disk with excellent linear responses and a considerable ME voltage coefficient has the potential for application in real‐time monitoring sensors.

Reversible Stimuli-Dependent Aggregation-Induced Emission from a "Nonfluorescent" Amphiphilic PVDF Graft Copolymer.

A poly(vinylidine fluoride) graft random copolymer of t-butyl aminoethyl methacrylate (tBAEMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA, Mn = 300) [PVDF-g-P(tBAEMA-ran-OEGMA), PVBO] is synthesized by atom transfer radical polymerization (ATRP), and PVBO is fractionated to get a highly water-soluble fraction (PVBO-1) showing a reversible on/off fluorescence behavior with gradual increase and decrease in pH, respectively, achieving a maximum quantum yield of 0.18 at pH = 12. PVBO-1 dissolved in water shows large multimicellar aggregates (MMcA), but at pH 12, crumbling of larger aggregates to much smaller micelles occurs, forming nonconjugated polymer dots (NCPDs), as supported by transmission electron microscopy and dynamic light scattering study. The reversible fluorescence on/off behavior also occurs with the decrease and increase of temperature. Theoretical study indicates that, at high pH, most of the amino groups become neutral and exhibit a strong tendency to form aggregates from crowding of a large number of carbonyl and amine groups, minimizing the HOMO-LUMO gap, showing an absorption peak at the visible region, and generating aggregation-induced emission.

Magnetic Field Sensing Based on Magnetoelectric Coupling of Ampere Force Effect With Piezoelectric Effect in Silver/Poly(Vinylidine Fluoride)/Silver Laminated Composite

With the advantages of large piezoelectric constant, wide frequency response range and good flexibility, Poly(vinylidine fluoride) (PVDF) is receiving heightened attention as a promising alternative to traditional piezoelectric materials. This paper focuses on investigating the magnetoelectric effect of a three-layer composite consisting of a core layer of PVDF and two layers of silver-plated electrodes under the action of AC and DC magnetic fields. The resonance frequency of the measurement system is firstly determined to obtain the maximum magnetoelectric response. Then, the existence of magnetoelectric effect in the laminated sample is further verified, which is realized through the coupling of the piezoelectric effect and the Ampere forces caused by the eddy current under the DC bias magnetic field. The experimental results show that the magnetoelectric voltage has an excellent linear response to both AC and DC magnetic fields. The magnetoelectric voltage coefficient is obtained as 299.97 mV/cm·Oe at the resonance frequency under the DC magnetic field of 1000 Oe amplitude. Besides, the theoretical model of the magnetoelectric energy conversion is established, which matches well with the experimental results. Consequently, both AC and DC magnetic field sensing can be realized by observing the magnetoelectric voltage. Without requiring a magnetostrictive phase and power supply, the three-layer composite with a considerable magnetoelectric effect is promising for the application of online monitoring sensors used in the smart grid.

Poly (vinylidine fluoride) (PVDF)/Potassium Sodium Niobate (KNN) nanorods based flexible nanocomposite film: Influence of KNN concentration in the performance of nanogenerator

Abstract Here we report the development of Potassium Sodium Niobate (KNN) nanorods (NRs) @ Poly (vinylidene fluoride) (PVDF) nanocomposite film based flexible piezoelectric nanogenerator where the percentage of KNN nanorods incorporation into PVDF matrix has been varied systematically to observe its direct effect on energy harvesting efficiency. 10% KNN NRs @ PVDF composite film possesses the highest electroactive (β-crystal) phase (~98%) as compared to other KNN percentage incorporated samples. The dielectric constant (e) value (~23) and the energy density (0.053 J/cm3 at an electric field of 164 kV/cm) are also found to be higher in the case of 10% KNN NRs @ PVDF composite film as compare to either lower or higher level of KNN percentage used. In addition, non-poled 10% KNN NRs @ PVDF composite film is capable to generate 3.4 open circuit voltage and 0.100 μA current by applying repeated compressive force into it. The developed nanogenerator shows the current density of 0.025 μA/cm2.

Enhancement of magnetic properties of PVDF by synthesize nano composite using NiZn ferrite

The (XRD) patterns of the samples Ni0.5Zn0.5Fe2O4 in the form of powder were prepared using the ball milling technique for 41, 67 and 90 hours and were annealed at 1073, 1273 and 1373 K and (Poly vinylidine Fluoride) (PVDF) and composite samples of x% Ni0.5Zn0.5Fe2O4/PVDF, (x% = 5, 10, 15, 20 and 25%) have been studied. The α phase decrease and β-phases increase by increasing the ferrite content suggesting less crystallinity producing an amorphous structure of PVDF at x = 25% ferrite where as β PVDF nucleates in the composites The electric polarization increases by increasing NZF content. The transition from ferromagnetic (order state) to paramagnetic (disorder state) occurs at Curie temperature TC (600K). The DC resistivity is nearly constant from 153k to 286k for all composite samples and then decreases at high temperature. The behavior of dielectric constant and dielectric loss was measured in the temperature range from 200K to 700K. With the increase of magnetic content, the saturation magnetization (Ms) value of the composites also increases.

Electrospun poly(vinylidene fluoride)/cellulose acetate/AgTiO2 nanofibers polymer electrolyte membrane for lithium ion battery

Polymer electrolyte membrane based on cellulose acetate/AgTiO2 seems propitious for lithium ion battery (LIB) separator due to its superior thermal stability and hydrophilic property. Herein, we report the preparation of novel electrospun poly(vinylidine fluoride)/cellulose acetate/AgTiO2 hybrid nanofibers polymer electrolyte membrane by electrospinning for LIB application. For the preparation of PVdF/CA-AgTiO2 nanofibers membrane, silver doped titania (Ag-TiO2) nanoparticles were incorporated in electrospinning solution of poly(vinylidine fluoride) (PVdF)/cellulose acetate (CA). The PVdF/CA-AgTiO2 nanofibers membrane was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FTIR), thermogravimetry (TG) and differential scanning calorimetry (DSC) analyses. PVdF/CA-AgTiO2 nanofibers membrane shows excellent thermal stability, high porosity and super electrolyte compatibility. The prepared cell LiFePO4/PVdF/CA-Ag-TiO2/Li delivered excellent cyclic stability with high discharge capacity and coulombic efficiency of 100% after 50 cycles at 0.1C. High ionic conductivity and good overall electrochemical performances enlightens the approach of making hybrid organic cellulose-based composite polymer electrolyte membrane is promising candidate for lithium ion battery.

Improved performance of silver doped titania/poly(vinylidine fluoride) nanofibers polymer electrolyte for lithium ion battery

Novel hybrid nanofibrous polymer electrolyte with high ionic conductivity and excellent electrochemical performance is developed by two step hydrothermal and electrospinning process. As-synthesized silver doped titania (Ag-TiO2) nanoparticles were incorporated in electrospinning solution of poly(vinylidine fluoride) for the preparation of Ag-TiO2/PVdF nanofibers. As-fabricated Ag-TiO2/PVdF nanofibers have been characterized by scanning electron microscopy with energy dispersive x-ray spectroscopy. Ag-TiO2 nanoparticles incorporated PVdF has advantages of both large surface area of nanoparticles and interlaying porous structure of nanofibers which is desirable for stable performance of battery. The prepared cell LiFePO4/Li with electrolyte Ag-TiO2/PVdF delivered excellent cyclic stability with high discharge capacity and coulombic efficiency of 100% after 50 cycles at 0.1 C as compared that of pure PVdF and TiO2/PVdF electrolytes. The hybrid Ag-TiO2/PVdF polymer electrolytes are expected to be a promising candidate for lithium ion battery.

Influence of Microstructure on the Nanomechanical Properties of Polymorphic Phases of Poly(vinylidene fluoride).

Poly(vinylidine fluoride) (PVDF) is a semicrystalline polymer which is known to exist in several polymorphic phases, namely, α, β, and γ. Each one of these polymorphic phases is characterized by unique features such as spherulite formation in the case of the α and γ phases and the presence of large piezoelectric and ferroelectric activity in the β phase. Despite being widely used as thin coatings in sensors, lack of reports on nanomechanical properties suggests that investigation of mechanical properties of PVDF, let alone those of its polymorphic phases, seems to have evaded the sight of the research community. Herein, we report the nanomechanical properties of the α, β, and γ phases of PVDF. The modulus and hardness values were evaluated from nanoindentation experiments; it was found that the electroactive β phase is the softest among the three polymorphic phases. This result was further confirmed by scratch experiments. We have attempted to establish a correlation between the microstructure and nanomechanical properties of these phases. This work sheds light on the mechanisms responsible for the observed mechanical behavior and the role of tie molecules and amorphous content in providing flexibility to the polymer.

Fabrication of hybrid gel nanofibrous polymer electrolyte for lithium ion battery

Fibrous membranes are promising separators for high-performance lithium ion battery because of their high porosity and superior electrolyte uptake. In this paper, the fabrication of hybrid gel polymer electrolyte (HGPE) by introducing SnO2 nanoparticles in poly(vinylidine fluoride) by electrospinning technique and soaking the electrospun nanofibrous membranes in 1 M LiPF6 in ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, v/v). The as-prepared electrospun HGPE with SnO2 nanofiller was characterized by scanning electron microscopy. The influence of SnO2 on the structure of polymer membrane, physical, and electrochemical properties is systematically investigated. HGPE shows significant high ionic conductivity 4.6 × 10[Formula: see text] S/cm at room-temperature and better cell performance such as discharge C-rate capability and cycle performance. The hybrid gel polymer nanofibrous membrane favors high uptake of lithium electrolyte so that electrolyte leakage is reduced. The gel polymer electrolyte with SnO2 filler was used for the fabrication of Li/PVdF-SnO2/LiFePO4 coin cell. The fabricated cell was evaluated at a current density of 0.2 C-rate and delivered stable and excellent cycle performance. This study revealed that the prepared HGPE can be employed as potential electrolyte for lithium ion batteries.

Amorphous SiO2 NP-Incorporated Poly(vinylidene fluoride) Electrospun Nanofiber Membrane for High Flux Forward Osmosis Desalination.

Novel amorphous silica nanoparticle-incorporated poly(vinylidine fluoride) electrospun nanofiber mats are introduced as effective membranes for forward osmosis desalination technology. The influence of the inorganic nanoparticle content on water flux and salt rejection was investigated by preparing electrospun membranes with 0, 0.5, 1, 2, and 5 wt % SiO2 nanoparticles. A laboratory-scale forward osmosis cell was utilized to validate the performance of the introduced membranes using fresh water as a feed and different brines as draw solution (0.5, 1, 1.5, and 2 M NaCl). The results indicated that the membrane embedding 0.5 wt % displays constant salt rejection of 99.7% and water flux of 83 L m(-2) h(-1) with 2 M NaCl draw solution. Moreover, this formulation displayed the lowest structural parameter (S = 29.7 μm), which represents approximately 69% reduction compared to the pristine membrane. Moreover, this study emphasizes the capability of the electrospinning process in synthesizing effective membranes as the observed water flux and average salt rejection of the pristine poly(vinylidine fluoride) membrane was 32 L m(-2) h(-1) (at 2 M NaCl draw solution) and 99%, respectively. On the other hand, increasing the inorganic nanoparticles to 5 wt % showed negative influence on the salt rejection as the observed salt flux was 1651 mol m(-2) h(-1). Besides the aforementioned distinct performance, studies of the mechanical properties, porosity, and wettability concluded that the introduced membranes are effective for forward osmosis desalination technology.

Lithium Iron Phosphate Nanosheet Nests As Cathode Material for Li-Ion Batteries

Nano Electrochemistry Laboratory, College of Engineering, The University of Georgia, Athens, GA 30602. Lithium-ion batteries are the current state-of-the-art energy storage technology for advanced electric vehicles and portable power applications due to their high energy density. The need for low cost lithium ion batteries has driven the development of inexpensive LiFePO4 cathodes, which offer a relatively high specific capacity (170 mAh·g-1) and relatively high discharge potential plateau (3.45 V) at a fraction of the cost of other materials. In additional to the low electrical conductivity, one of the major drawbacks of this material is the inherently slow lithium diffusion. Unlike spinel or layered structures, the olivine structure of LiFePO4 allows lithium diffusion in only one direction and therefore severely limits the intercalation rate due to slow solid-state diffusion. This limitation could be overcome by de-sizing the material in the < 010 >, the direction of diffusion. This can be achieved by synthesizing LiFePO4 nanosheet nests (LFP-NSN) using a directed growth method adapted and modified from a synthesis procedure reported earlier.1 Figure 1 shows the scanning electron microscopy (SEM) image of the LFP-NSN synthesized by our modified procedure. Figure 2 shows the X-ray diffraction (XRD) pattern of the synthesized LFP-NSN, which compares well with the XRD pattern of orthorhombic, olivine-type LiFePO4 from the library. For battery testing, the synthesized structures were mixed in a ratio 80:10:10 of LFP-NSN: Super C carbon: poly(vinylidine fluoride) in N-methyl pyrrolidone to form a slurry that was cast on aluminum foil to be used as the cathode in CR2032 lithium ion coin cells for testing and evaluation. Fig. 1: a) SEM image and b) XRD pattern (black) with LiFePO4 characteristic peaks identified in red of LFP-NSN synthesized by a solvothermal reaction. Acknowledgements: The authors would like to thank Dr. Tina Salguero and Dr. Zhengwei Pan for their help in this project. * Corresponding Author: rama@uga.edu Reference: 1. Y. Zhao, L. Peng, B. Liu and G. Yu, Single-Crystalline LiFePO4 Nanosheets for High-Rate Li-Ion Batteries. Nano letters 2014, 14, 2849-2853. Figure 1

Microporous poly(vinylidene fluoride) hollow fiber membranes fabricated with PolarClean as water-soluble green diluent and additives

Methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (RhodiasolvⓇ PolarClean) as a water-soluble green solvent was used for the first time to prepare poly(vinylidine fluoride) (PVDF) hollow fiber membranes. Due to the solubility of PolarClean in water, a combination of thermally induced phase separation and non-solvent induced phase separation was observed during the membrane formation. The effects of additives such as poly(vinyl pyrrolidone) (PVP) with different molecular weights (10k, 55k, 360k and 1300k) and glycerol (5wt% and 15wt%) were studied at different quenching bath temperatures (5, 15 and 25°C). The properties of the hollow fiber membranes, such as their morphology, roughness, mechanical properties, overall porosity, water permeability, polymorphism in the skin layer and polymorphism in the bulk of the membrane structure were investigated as well. A phase diagram for the PVDF/PolarClean system showed the PVDF crystallization temperature around 53°C. PolarClean along with additives induces porous structure and the formation of β-polymorphs in the membranes, resulting in high water permeability.

Improvement of Electrochemical Performance of Bilirubin Oxidase Modified Gas Diffusion Biocathode by Hydrophilic Binder

Performance of bilirubin oxidase (BOD) modified gas diffusion biocathode has been highly improved by incorporating a hydrophilic polymer as binder to form effective Ketjen black (KB)-immobilized structure for the enzyme reaction on carbon paper electrode. An aqueous dispersion of styrene-butadiene rubber latex with sodium carboxymethylcellulose (SBR/CMC) was employed as hydrophilic binder. In direct electron transfer system, the biocathode with SBR/CMC binder exhibited larger O2 reduction current in phosphate buffer solution (PBS, pH 7.0) at room temperature, compared with that of a poly(vinylidine fluoride) binder electrode, which is a typical hydrophobic polymer. Performance of the biocathode was further improved by utilizing mediator electron transfer system, and the maximum current density of ∼27 mA cm−2 was achieved in pH 5.0 PBS. These improvements are believed to be due to hydrophilic property of the KB-immobilized electrode surface by the SBR/CMC binder, leading to high-dispersion of BOD on the surface and also stable interface formation of O2 gas / enzyme / electrolyte during the reaction. Furthermore, we fabricated a glucose/O2 cell composed of the biocathode and an opposite bioanode with glucose oxidase. The full-cell successfully achieved mW-class power density of 5.22 mW cm−2 with an open-circuit voltage of 0.61 V in pH 7.0 PBS.

Fabrication and Characterization of Functionally Graded Poly(vinylidine fluoride)-Silver Nanocomposite Hollow Fibers for Sustainable Water Recovery

Fabrication and Characterization of Functionally Graded Poly(vinylidine fluoride)-Silver Nanocomposite Hollow Fibers for Sustainable Water Recovery

Ferroelectric and magnetic studies on unpoled Poly (vinylidine Fluoride)/Fe3O4 magnetoelectric nanocomposite structures

The fabrication of flexible Poly (vinylidine Fluoride)/Fe3O4 magnetoelectric nanocomposite films with different weight fractions of Fe3O4 nanoparticles is explained in this paper. The effects of nano Fe3O4 content on the structural, chemical, thermal, and magnetoelectric properties of PVDF matrix are discussed. XRD and FTIR results reveal the interaction between the filler and the matrix and also they suggest that the β phase contribution can be significantly controlled by the inclusion of nano Fe3O4. Thermal stability and melting point behavior of the composite films are investigated through TG/DTA. The existence of ferrimagnetism and ferroelectric properties in the films are proved through the magnetization and polarization studies. The hysteresis loops show the largest polarization and magnetization values at 0.14 wt% of Fe3O4. Also, the dependence of ferroelectric polarization on temperature is investigated and reported.

PVDF/PMMA brushes membrane for lithium‐ion rechargeable batteries prepared via preirradiation grafting technique

AbstractPoly(methyl methacrylate) (PMMA) was anchored to multiporous poly(vinylidine fluoride) (PVDF) surface via electron beam preirradiation grafting technique to prepare PVDF/PMMA brushes. The conformation of the PVDF/PMMA brushes was verified through Attenuated total reflection‐Fourier transform infra red spectroscopy (ATR‐FTIR), energy dispersive X‐ray spectroscopy (EDX), and scanning electron microscopy (SEM). Thermal stability of PVDF/PMMA brushes was characterized by thermo gravimetric analysis (TGA). The degradation of PVDF/PMMA brushes showed a two‐step pattern. PVDF/PMMA brushes membrane could be used as polymer electrolyte in lithium‐ion rechargeable batteries after it was activated by uptaking 1 M LiPF6/EC‐DMC (ethylene carbonate/dimethyl carbonate; EC:DMC = 1:1 by volume) electrolyte solution. The activated membrane showed high ionic conductivity, 6.1 × 10−3 S cm−1 at room temperature, and a good electrochemical stability up to 5.0 V. The excellent performances of multiporous PVDF‐g‐PMMA membranes suggest that they are suitable for application in high‐performance lithium‐ion batteries. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 751–758, 2008

Effect of flow history on poly(vinylidine fluoride) crystalline phase transformation

AbstractThis study was devoted to the effect of extensional flow during film extrusion on the formation of the β‐crystalline phase and on the piezoelectric properties of the extruded poly(vinylidine fluoride) (PVDF) films after cold drawing. The PVDF films were extruded at different draw ratios with two different dies, a conventional slit die and a two‐channel die, of which the latter was capable of applying high extensional flow to the PVDF melt. The PVDF films prepared with the two‐channel die were drawn at different temperatures, strain rates, and strains. The optimum stretching conditions for the achievement of the maximum β‐phase content were determined as follows: temperature = 90°C, strain = 500%, and strain rate = 0.083 s−1. The samples prepared from the dies were then drawn under optimum stretching conditions, and their β‐phase content and piezoelectric strain coefficient (d33) values were compared at equal draw ratios. Measured by the Fourier transform infrared technique, a maximum of 82% β‐phase content was obtained for the samples prepared with the two‐channel die, which was 7% higher than that of the samples prepared by the slit die. The d33 value of the two‐channel die was 35 pC/N, which was also 5 pC/N higher than that of the samples prepared with the slit die. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Lithium ion conduction in PVC–LiN(CF3SO2)2 electrolytes gelled with PVdF

Hybrid, solid polymer electrolyte films consisting of poly(vinyl chloride) (PVC), poly(vinylidine fluoride) (PVdF), LiN(CF3SO2)2 and ethylene carbonate (EC) are prepared using solvent casting technique. The formation of polymer–salt complex has been confirmed by FTIR spectral studies. The effect of the PVC/PVdF blend ratio on ionic conductivity is explained in terms of the morphology of the film. The highest ionic conductivity value (5.766×10−3 S cm−1) is obtained for PVC–PVdF–LiN(CF3SO2)2–EC (Film F3) at room temperature. The electrochemical stability window of Film F3 was about 4.5 V determined from the linear sweep voltammetry plot. The surface morphology of the above membrane was also observed by scanning electron microscope (SEM). Polymer electrolyte film bereft of PVC appears very promising for Li battery applications.