Thin Polyvinylidene Fluoride Research Articles

Highly aligned thin PVDF/Cloisite 30B nanofibers as a piezoelectric sensor

One-dimensional confined nanostructures with intense dipole orientation exhibit enhanced piezoelectric performance compared to traditional three-dimensional bulk films. Herein, we show that preparing highly aligned thin polyvinylidene fluoride (PVDF) nanofibers in the presence of a small amount of organically modified clay (Cloisite 30B) platelets induces a significant crystal polymorphism alteration from non-polar α-phase to polar β-phase rather than the randomly oriented neat PVDF nanofibers with a larger average diameter. It has been detected that the nanofiber orientation considerably contributes to the enhanced degree of crystallinity and mechanical properties. Also, the PVDF-Cloisite 30B interactions caused an improvement in the elastic modulus. The piezoelectric performance of the electrospun nanofibers was examined by sensing characteristics. It was found that the synergistic effects of nanofiber orientation and clay platelets efficiently improve sensing performance via the piezoelectric dipole orientation mechanism.

Effects of Film Confinement on Dielectric and Electrical Properties of Graphene Oxide and Reduced Graphene Oxide-Based Polymer Nanocomposites: Implications for Energy Storage

2D nanofillers such as graphene oxide (GO) and reduced GO (rGO)-based polymer nanocomposites have emerged as crucial materials for various applications, from flexible solid-state capacitors to electromagnetic interference (EMI) shielding devices. Specifically, the dielectric breakdown strength (EBD) and dielectric constant of polymer nanocomposite capacitors determine their ability to store energy, whereas frequency-dependent loss is crucial for EMI shielding applications. The miniaturization of energy storage and electronic devices demands a detailed understanding of the behavior of these polymer nanocomposites in the thin-film regime (micron to sub-micron thicknesses). In this work, we demonstrate the effect of confinement on the dielectric, electrical, and capacitive energy storage properties of the polyvinylidene fluoride (PVDF)–GO and PVDF–rGO films. We show that the dielectric permittivity is significantly impacted by the nanofiller confinement in thin (≈1 μm) PVDF polymer films, which is comparable to the lateral dimension of these 2D nanofillers. In thin PVDF–GO films, the nanofillers (and associated surface dipoles) become oriented quasi-parallel to the film interfaces, affecting the relative projected area to the applied electric field. The conductivity and loss tangent values increased as a function of frequency with reduced film thickness, which is beneficial to EMI shielding application. The EBD of the confined GO-based films was found to be relatively independent of the filler fraction, whereas rGO-based films increased with the filler fraction after an initial decrease. These results provide fundamental insights into rational design principles for using ultrathin GO and rGO-based polymer nanocomposite films in next-generation flexible electronic and energy storage devices.

Designing of the green γ-AlOOH@Naringin thin film composite PVDF based nanofiltration membrane and application for pharmaceutical wastewater treatment

Herein, the green naringin functionalized boehmite (γ-AlOOH@Nar) bionanocomposite was used to fabricate the high-performance thin film composite (TFC) polyvinylidene fluoride (PVDF) based nanofiltration (NF) membrane with enhanced antifouling properties and pharmaceutical rejection. For this aim, the PVDF NF membrane was first activated by triazinyl groups. Then the membrane surface was subsequently functionalized by the γ-AlOOH@Nar nanocomposite at different concentrations (0.2, 0.4, and 0.6 wt%). The γ-AlOOH@Nar TFC NF membranes were characterized by means of Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscope (AFM), zeta potential, and thermogravimetric analysis (TGA). Moreover, the mean pore radius, porosity, surface hydrophilicity, salt rejection, pure water flux, and antifouling properties of the membranes were investigated. The 0.4 wt% γ-AlOOH@Nar TFC (TFC-0.4) membrane showed a pure water flux of 53.6 L/m2h and FRR of 95.4%, which were about 2.3 and 2.4 times that of the blank membrane. The TFC-0.4 membrane not only provided the highest permeability and surface hydrophilicity but also lowered the irreversible fouling ratio while keeping high pharmaceuticals rejection (99.8% for both Ceftriaxone (CTX) and cephalexin (CEX)). The pharmaceutical wastewater filtration showed that the γ-AlOOH@Nar TFC membranes achieved high normalized flux and also provided 89.8% COD removal, 100% turbidity removal, and moderate TDS removal (53.0%). Overall, the γ-AlOOH@Nar TFC membranes exhibited high separation performance and excellent antifouling properties showing their great potential for use in pharmacutical wastewater treatment facilities.

Effects of Porosity on Piezoelectric Characteristics of Polyvinylidene Fluoride Films for Biomedical Applications.

Objective: The objective of this work is to study the effects of porosity on mechanical and piezoelectric properties of polyvinylidene fluoride (PVDF) films for biomedical applications. Impact Statement: By investigating the piezoelectric properties of PVDF and the porosity effect on its electromechanical performance, there is potential for further development of PVDF as a hemodynamic sensor that can lead to further technological advancements in the biomedical field, benefiting patients and physicians alike. Introduction: PVDF thin films have shown potential in the application of hemodynamic flow sensing and monitoring the effects on blood flow caused by prosthetic valve implantation via the transcatheter aortic valve replacement operation. The piezoelectric performance of PVDF films can be influenced by the porosity of the material. Methods: In this study, strain tracking was performed on thin film PVDF specimens with various levels of porosity and pore sizes to determine the mechanical properties of the specimens. The mechanical properties were used to model the PVDF material in COMSOL multiphysics software, in which compression test simulations were performed to determine the piezoelectric coefficient d33 of the PVDF. Results: A decline in the elastic modulus was found to be highly inversely correlated with porosity of the specimens and the simulation results show that elastic modulus had a much greater effect on the piezoelectric properties than Poisson's ratio. Conclusion: A combination of experimental and computational techniques was able to characterize and correlate the mechanical properties of PVDF films of varying porosities to their piezoelectric properties.

Harvesting airflow energy from circular cylinder wake via a thin polyvinylidene fluoride film

To improve the characteristics of airflow energy harvesting, this paper presents a new piezoelectric wind energy harvester (PWEH), in which a polyvinylidene fluoride (PVDF) film was directly located in the wake of the circular cylinder. Four important parameters were independently varied for detailed experimental investigations: wind speed, spacing ratio for the distance between the center of the circular cylinder and the tip of the PVDF film to the circular cylinder diameter, diameter of the circular cylinder, and load resistance. The results indicated that the designed PWEH performed optimally with the occurrence of resonance, maintaining a relatively high output when significantly exceeding the resonance wind speed. The PVDF film inhibited the vortex shedding of the circular cylinder, which weakened with increasing spacing ratio. The optimum value of the spacing ratio should be approximately 2.5, which yields an effective coupling between the vortex and structure. The diameter of the circular cylinder played an important role in determining the output power. The match between the load resistance and PWEH also contributed to the high-level performance. Moreover, with an increase in the diameter of the circular cylinder, the increasing blockage ratio unexpectedly enhanced the vortex shedding frequency and decreased the theoretical resonance wind speed, which provided a new orientation for improving the performance of such PWEHs.

Fabrication of Biopolymer-Based Piezoelectric Thin Film From Chitosan Using Solvent Casting Method

The application of biopolymer in piezoelectric application provides a great potential to replace traditional piezoelectric substances like polyvinylidene fluoride (PVDF) and lead zirconate titanium (PZT), because of their biodegradability, biocompatibility, low toxicity properties and sustainable production. Chitosan, a natural polysaccharide has been found to fulfil all the characteristics and can be used safely for piezoelectric applications in agricultural, food industries and biomedical fields. This study aims to assess how piezoelectric characteristics are affected by different acid solvents and solvent casting volumes during chitosan thin film production. Chitosan thin film prepared using acetic acid and formic acid were fabricated using solvent casting method on petri dish at different volume of acids solvent. Chitosan thin films produced using acetic acid and 25 mL solvent loading provided the most significant mechanical quality factor (2.8). Moreover, the dissipation factor (0.80) was the lowest, indicating comparability to traditional thin PVDF film piezopolymer. Hence, thin chitosan films produced using acetic acid is proven to have the potential in piezoelectric application

Research on Measurement of Transformer Short-Circuit Force Using Piezoelectric Thin Film Polyvinylidene Fluoride Sensor

This paper presents a newly designed piezoelectric thin film polyvinylidene fluoride (PVDF) sensor that is able to measure short-circuit force directly in a short-circuit test. The sensor, with its advantages of high sensitivity, thin shape and shock-resistant, could measure the axial and radial short-circuit force which is usually difficult to measure due to large voltage and small gap between transformer windings during a short-circuit test, and thus provides a good way to study the ability of transformers to withstand short circuit, in which case many transformer accidents are caused. In the first part the working principle of PVDF sensor and the design of PVDF sensor in transformers are described. The following part introduces the calculation and simulation of the sensor and the short-circuit force. A real short-circuit test with PVDF sensor is then recorded and analyzed in the following part. And it is finally concluded that the piezoelectric thin film PVDF sensor is proved to have high accuracy in the measurement of the short-circuit force of transformer.

Polyvinylidene fluoride coated optical fibre for detecting perfluorinated chemicals

This work reports the development of a Fabry-Perot Interferometry (FPI) based optical fibre to detect perfluorooctanoic acid (PFOA) and other perfluoroalkyl substances (PFAS) in aqueous solutions. A novel and simple sensor fabrication procedure utilizing an immersion precipitation-based phase inversion process to form a thin polyvinylidene fluoride (PVDF) coating at the end-faces of freshly cleaved optical fibres is presented. The PVDF coating was rich in the electroactive β-phase, which enhances dipole-dipole and hydrophobic interaction with PFAS at binding sites. Sensor testing with model PFOA solutions showed that the PVDF coated FPI optical fibre can detect PFOA. The change in optical path difference (OPD) with change in PFOA concentration was considered as a measure of sensitivity and it corresponded to a value of 0.9–5 nm/ppm for PFOA. In real PFAS solutions obtained from fire-fighting foams, the OPD was found to be significantly more sensitive at 178 nm/ppb.

Sandwich-like sound-driven triboelectric nanogenerator for energy harvesting and electrochromic based on Cu foam

As a kind of environmental dissipative energy, acoustic energy is common but difficult to collect and utilize effectively owing to its low energy density and special acoustic state. In this work, a new type of triboelectric nanogenerator (TENG) based on porous foam copper with sandwich-like friction pairs is designed to harvest sound energy efficiently from the environment. The sound-driven TENG is mainly composed of Cu foam, polyvinylidene fluoride (PVDF) nanofibers and nylon fabric, in which the Cu foam is used as a sound collector, conductor and amplifier, as well as the friction layer and conductive layer of the TENG. The thin and light PVDF nanofiber membrane and nylon fabric are used as vibration membranes, which are easy to generate vibration under weak sound to harvest the sound energy under wideband frequencies. This sound-driven TENG shows high triboelectric output performance with a maximum current density up to 25.01 mA/m2 and a charging rate of 20.91 μC/s with a charging transformation efficiency up to 59.85%, which can light up 384 LEDs and drive an electrochromic device for reversible color changing. Importantly, the sound-driven TENG has good working stability. It can work continuously for 7 days under loudspeaker driving without decay. This type of sound-driven TENG has potential application in the field of audio frequency analysis, noise detection, energy supply and presents promising potential to be a self-powered system in the electrochemical industry.

The Influence of Polyvinylidene Fluoride (PVDF) Binder Properties on LiNi0.33Co0.33Mn0.33O2 (NMC) Electrodes Made by a Dry-Powder-Coating Process

We have investigated the effects of the molecular weight of the polyvinylidene fluoride (PVDF) binder on the electrochemical performance and mechanical integrity of the LiNi0.33Co0.33Mn0.33O2 (NMC) electrodes made by a dry-powder-coating process. The microstructure, binding strength, and electrochemical behavior of the electrodes made with two types of PVDF polymers were compared. We show that a thin PVDF layer can form on the NMC particle surface after heating the PVDF to above its melting point. The microstructure and porosity of the PVDF layer depend strongly on the molecular weight of the PVDFs. With increasing molecular weight, the PVDF layer becomes more porous, improving the high-rate capacity without decreasing binding strength and long-term cycling performance of the electrodes.

α- & β-crystalline phases in polyvinylidene fluoride as tribo-piezo active layer for nanoenergy harvester

The manuscript introduces the use of non-electrically polled spin-coated thin polyvinylidene fluoride (PVDF) films as the active layers in a contact electrification-based nanoenergy harvester. The four-layered device utilizes both piezo and triboelectric effect coupled with electrostatic induction. The elucidation of potential generation during contact between crystalline phases ( α and β) of PVDF layer material is investigated in the manuscript. Fourier transform infrared–attenuated total reflectance spectroscopy is carried out to illustrate the α- and β-phases in PVDF pellet, prepared film as well as the film after contact. Dynamic contact mode electrostatic force microscopy (DC-EFM) along with atomic force microscopy is used for the evaluation of reverse piezoelectric, local ferroelectric, triboelectric voltage and adhesive energy of the PVDF films before–after contact process. Quantum chemical calculation is performed using density functional theory to explain possible electron transitions in the active layers between the cylindrically symmetric α-phase and electrical double layer charges in the β-phase of PVDF. The interface study of the film is also carried out both experimentally using DC-EFM and through quantum chemical calculations. The fabricated device with the hybrid piezo-tribo layer promises to be a simple and low-cost energy source for the next-generation self-powered electronic devices. The device can also be used as knock sensor in engines as well as a capacitor.

Development of a PVDF Pressure Gauge for Blast Loading Measurement

We investigate the development of a sensor for dynamic pressure measurement. The sensor relies on a Bauer shock gauge of 25-μm thin Polyvinylidene fluoride (PVDF) film [AIP Conf. Proc 706:1121–1124, [21]. These gauges unfortunately require some skills to be integrated in an acquisition chain and the obtained results are strongly “experiment dependent.” In the presented work, the classical Bauer gauge has been adapted: the reproducible PVDF film is poled at high voltage, in electrical symmetrical response and reproducibility. The sensitive area is a 3 × 3 mm square. The gauge has been electrically shielded and overlaid with a heat conductive material. A 5-m long coaxial wire connects the gauge to a charge amplifier, allowing its connection to a deported oscilloscope. The output electrical charge of the PVDF gauge has been correlated with the pressure measured by calibrated PCB® sensors. Measured pressures are validated by an analytical approach and numerical simulations of the flow in the shock tube. A calibration curve can be deduced for pressures below 10 bar, values which are often met in blast loading situations. This customizable sensor is hence suitable and easy to use to measure the blast-reflected pressure on a flat material.

Flexible pyroelectric generators for scavenging ambient thermal energy and as self-powered thermosensors

Wasted heat is one of the most abundant and widely available energy sources in our living environment and industrial activities. A lot of attentions have been paid on harvesting ambient wasted thermal energy. In this work, a flexible PG (pyroelectric generator) based upon a thin PVDF (polyvinylidene fluoride) film has been fabricated. Based on the pyroelectric effect, the PG can harvest thermal energy arising from the time-dependent fluctuating temperature with spatial uniformity. At the temperature change of 50 K, the PG can deliver an open-circuit voltage of 8.2 V and a short-circuit current of 0.8 μA, respectively, with the maximal output power of 2.2 μW on a load of 0.1 MΩ, which can be utilized to directly drive a LCD (liquid crystal display) or LEDs (light emitting diodes), or to charge a commercial capacitor for subsequent usages. Moreover, the PG can be used to construct a self-powered thermosensor as a result of the linear relationship between the output voltage and the temperature change. Our study promotes the development of the PG for scavenging wasted thermal energy and opens up plenty of potential self-powered applications.

Formation of uniform PVDF fibers under ultrasound exposure in presence of anionic surfactant

Polyvinylidene fluoride (PVDF) was electrospun into fibrous membranes from its solutions in mixture of dimethylformamide (DMF) and acetone with and without an anionic fluorosurfactant. The results indicate that PVDF fibers contain a number of beads at any solvents compositions and solution concentrations. Addition of the surfactant does not affect considerably the morphology of fibers, however it helps to decrease the surface tension of the solution and reduce the beading of fibers. The most important factor affecting the fiber morphology is sonication. Sonication of the spinning solution promotes the formation of perfect, uniform, thin and cylindrical PVDF nanofibers without any beading.

Experiments and Modeling of Micro Flapping Wings of Different Designs in Hover

A low-order phenomenological model relating dynamic wing motion to thrust production of micro flapping wings with different stiffness was examined. The motivation is toward closed-loop flight control of flapping micro air vehicles. The low-order model was based on a “black box” state-space description that used the intraperiod flapping-wing motion as input to determine modeling coefficients that minimized the error between the predicted and actual intracycle thrust. The data time series used in the modeling were provided by a companion experiment with three flapping wings of different designs and stiffness. The wings were fabricated from laminated carbon-fiber strips that were covered by a thin polyvinylidene fluoride film sheet. The wings had a span of 12.5 cm and were attached to a commercial Cybird gearbox that could be operated at different flapping frequencies. Digital high-speed video was used to determine the dynamic displacement of the wing structure. The intraperiod wing displacement was quantified using digital image processing of each video frame. The low-order model successfully captured the dynamic thrust generation within a flapping cycle and produced the correct scaling of the peak thrust with flapping frequency for all three wing designs. The model mean thrust frequency scaling agreed with the experiments if the peak thrust was within approximately 40% of the cycle-averaged thrust. A modification of the model is suggested when that difference is too large.

Pyroelectric Sensor for Temperature Monitoring of Biological Fluids in Microchannel Devices

In a lab-on-a-chip application, the measurement of local temperature variation often involves the detection of very low-level signals in a noisy microscale environment. A polymer pyroelectric transducer represents an efficient solution in terms of speed, sensitivity, and scale of integration, especially when prompt and accurate temperature monitoring is desired. This paper presents a ferroelectric polymer sensor to be used for the measurement of temperature variations in a microfluidic system. The pyroelectric sensor is based on a thin polyvinylidene fluoride sheet, which also provides a seal for the microchannels. The analytical model of the pyroelectric response of the sensor, coupled with the microchannel device, is in a good agreement with experimental data. Experiments confirm that the operating temperature range is suitable for most applications in which fast temperature monitoring is desired in order to avoid degradation of the biological samples.

A Novel Texture Sensor for Fabric Texture Measurement and Classification

Surface texture is one of the important cues for human beings to identify different fabrics. This paper presents a novel design of a surface texture sensor by imitating human active texture perception by touch. A thin polyvinylidene fluoride (PVDF) film is used as the sensitive element to fabricate a high-accuracy, high-speed-response fabric surface texture sensor, and a mechanism is designed to produce the relative motion at a certain speed between the texture sensor and the surface of the perceived fabric with constant contact force. Thus, the surface texture property can be measured as the output charge of the PVDF film of the sensor induced by the small height/depth variation of the moving fabric surface. A texture feature extraction method by compressing the zero value spectral lines in frequency domain is proposed. In addition, a radial basis function (RBF) neural networks based on unsupervised K-means clustering algorithm is used as classifier for texture recognition. The experiments show that the proposed texture sensor is effective in detecting the feature signals of fabric surface textures, which are suitable for the RBF networks to classify the different fabrics.

Measurement of stress/charge coefficients of a thin polyvinylidene fluoride film

A new experimental/analytical approach is used to measure a piezoelectric coefficient of polyvinylidene fluoride (PVDF). This method is based on the volume displacement of a vibrating beam. The obtained value of the stress/charge coefficient is checked using modal coordinate measurement theory and finite element analysis. A PVDF film is cut into two sensors shape. These sensors measure, respectively, the volume displacement and modal coordinate of a simply supported beam vibrating at its first mode. An accelerometer and a force gauge are used to measure the volume displacement and the modal coordinate of the beam. Then, PVDF volume displacement sensor equation developed by Guigou et al. is used with the experimental data to find the stress/charge coefficient e31. This value of e31 is first checked using the PVDF modal sensor equation from Lee and Moon. Then, the anys finite element code is used to validate the method. Experimental value of e31 obtained at room temperature is presented and compared with existing data. Excellent agreement is found. The extension of the method to 2D structure to determine the value of e31 and e32 simultaneously is introduced.

Pd/PVDF thin film hydrogen sensor system based on photopyroelectric purely-thermal-wave interference

A novel sensitive solid-state sensor system for trace hydrogen gas detection has been developed as a next generation device to earlier photopyroelectric (PPE) hydrogen sensors. The basic principle of the sensor is based on the technique of PPE purely-thermal-wave interferometry recently developed in this Laboratory. The active element of the sensor is a thin polyvinylidene fluoride (PVDF) pyroelectric film, sputter-coated with Pd on one surface and with a Ni–Al alloy electrode on the other surface. Unlike the conventional PPE hydrogen sensors, this new sensor produces a coherent differential PPE signal in a single detector, rather than using two detectors (one active, the other reference) and complicated electronics. The measurement results show that the signal noise level, the detectivity and the signal dynamic range are improved by more than one order of magnitude compared with the conventional single-beam method. The operating characteristics have been examined for three different thicknesses of Pd coating on the same thickness PVDF-film detector. The signal generating mechanism, attributed to the change of the optical absorptance of the Pd coating when exposed to hydrogen, and/or the shift in the Pd work function, is also discussed.

Measurement of sound velocity and thickness of thin samples by time-resolved acoustic microscopy

Simultaneous measurement of sound velocity and thickness of thin specimens is a well-known technique in time-resolved acoustic microscopy. However, the applicability is restricted, because a substrate in contact with the back of the sample is required. Furthermore, the substrate must have an uncoated area, because a reference signal from the substrate’s surface is needed. To overcome these performance limitations, a technique has been developed that focuses the lens on the front and afterwards on the back of the sample. An equation for the longitudinal sound velocity of thin samples has been analytically deduced using this approach. Having calculated the sound velocity, the thickness of the sample directly follows using known relations. Additionally, the developed method has been experimentally applied to thin polyvinylidene fluoride film. The results confirm the capability of the method.