Piezoelectric Polymer Polyvinylidene Fluoride Research Articles

Preparation and Structure-Property Relationship Study of Piezoelectric-Conductive Composite Polymer Nanofiber Materials for Bone Tissue Engineering.

This study aimed to develop Janus-, cross-network-, and coaxial-structured piezoelectric-conductive polymer nanofibers through electrospinning to mimic the piezoelectricity of bone and facilitate the conduction of electrical signals in bone tissue repair. These nanofibers were constructed using the piezoelectric polymer polyvinylidene fluoride, and the conductive fillers reduced graphene oxide and polypyrrole. The influence of structural features on the electroactivity of the fibers was also explored. The morphology and components of the various structural samples were characterized using SEM, TEM, and FTIR. The electroactivity of the materials was assessed with a quasi-static d33 meter and the four-probe method. The results revealed that the piezoelectric-conductive phases were successfully integrated. The Janus-structured nanofibers demonstrated the best electroactivity, with a piezoelectric constant d33 of 24.5 pC/N and conductivity of 6.78 × 10-2 S/m. The tensile tests and MIP measurements showed that all samples had porosity levels exceeding 70%. The tensile strength of the Janus and cross-network structures exceeded that of the periosteum (3-4 MPa), with average pore sizes of 1194.36 and 2264.46 nm, respectively. These properties indicated good mechanical performance, allowing material support while preventing fibroblast invasion. The CCK-8 and ALP tests indicated that the Janus-structured samples were biocompatible and significantly promoted the proliferation of MC3T3-E1 cells.

Research progress of piezoelectric polymer PVDF in sound absorption technology

Owing to its impedance properties and piezoelectric effect, the piezoelectric polymer polyvinylidene fluoride (PVDF) finds application in the field of noise control. Traditional sound-absorbing materials have gradually fallen short of the demands of sound-absorbing functionality and environmental adaptability in today’s increasingly acute noise pollution environment. When PVDF is added to sound absorption, materials or structures have an additional loss path for the conversion of sound energy to electric energy. This helps to increase the low-frequency sound absorption band and improve low-frequency sound absorption performance. Through the action of viscosity, friction, relaxation, piezoelectric effect, and dielectric loss, the sound energy in the passive sound-absorbing material containing PVDF is transformed into energy dissipation in the form of heat energy, electric energy, and so on under the matching of PVDF low impedance. In active control, secondary sound and force sources can be supplied by PVDF-based transducers and actuators to reduce noise. This paper first provides an overview of the piezoelectric characteristics of β-phase PVDF and its optimization techniques. It then goes on to discuss the use of PVDF in passive sound-absorbing materials, active controls, and hybrid sound absorption systems. Finally, it summarizes the benefits, issues that still need to be resolved, and future directions for these three noise reduction techniques.

Optimizing solvent dipole moment enables PVDF to improve piezoelectric performance

The all-trans conformation (β-phase) possesses a significant impact on the piezoelectric polymer polyvinylidene fluoride (PVDF). Inducing more molecular chain [−CH2−CF2−]n to form all-trans conformation is one of the biggest obstacles for manufacturing high-performance piezoelectric sensing devices. Herein, the continuous vacuum technology is used to modulate the polarity of binary solvents by the proportion of the lower solvent. The regulated solvent forms a high dipole moment, an interaction between the dipole of β-phase and the dipole moment makes the phase reversal in PVDF. Fourier transform infrared spectroscopy, piezoelectric constant test and other characterization results show that when the weakly polar acetone and the strongly polar solvent DMF reach a ratio of 4:6, the pure PVDF film possesses high piezoelectricity (d 33 ∼ −44.8 pC N−1) and strong self-polarization. Additionally, the A4D6 device exhibits high sensitivity (S 1 = 0.182 V/N, 0.5 N ∼ 30 N), driven capability (0.49 mW m−2), and reliability during the electrical tests as a pressure device. This work provides an effective and cost-effective route of optimizing the solvent’s polarity to improve the piezoelectric characteristics of the polymer.

Structure-Property Relationship of Piezoelectric Properties in Zeolitic Imidazolate Frameworks: A Computational Study.

Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials with very high structural tunability. They possess a very low dielectric permittivity εr due to their porosity and hence are favorable for piezoelectric energy harvesting. Even though they have huge potential as piezoelectric materials, a detailed analysis and structure-property relationship of the piezoelectric properties in MOFs are lacking so far. This work focuses on a class of cubic non-centrosymmetric MOFs, namely, zeolitic imidazolate frameworks (ZIFs) to rationalize how the variation of different building blocks of the structure, that is, metal node and linker substituents affect the piezoelectric constants. The piezoelectric tensor for the ZIFs is computed from ab initio theoretical methods. From the calculations, we analyze the different contributions to the final piezoelectric constant d14, namely, the clamped ion (e140) and the internal strain (e14int) contributions and the mechanical properties. For the studied ZIFs, even though e14 (e140 + e14int) is similar for all ZIFs, the resultant piezoelectric coefficient d14 calculated from piezoelectric constant e14 and elastic compliance constant s44 varies significantly among the different structures. It is the largest for CdIF-1 (Cd2+ and -CH3 linker substituent). This is mainly due to the higher elasticity or flexibility of the framework. Interestingly, the magnitude of d14 for CdIF-1 is higher than II-VI inorganic piezoelectrics and of a similar magnitude as the quintessential piezoelectric polymer polyvinylidene fluoride.

Piezoelectric Nanogenerator Based on Electrospinning PVDF/Cellulose Acetate Composite Membranes for Energy Harvesting.

The organic piezoelectric polymer polyvinylidene fluoride (PVDF) has attracted extensive research because of its excellent flexibility and mechanical energy-harvesting properties. Here, the electrospinning technique was taken to fabricate synthesized fiber membranes of a PVDF/cellulose acetate (CA) composite. The obtained PVDF/CA electrospun fiber membranes (EFMs) were employed to prepare a flexible nanogenerator. XRD and FTIR spectroscopy revealed the enhancement of piezoelectric behavior due to an increase in β-phase in PVDF/CA EFMs compared with cast films. The PVDF/CA fibers (mass ratio of PVDF to CA = 9:1) showed an output voltage of 7.5 V and a short-circuit current of 2.1 μA under mechanical stress of 2 N and frequency of 1 Hz, which were 2.5 and two times greater than those of the pure PVDF fibers, respectively. By charging a 4.7 µF capacitor for 15 min with the voltage generated by the PVDF/CA EFMs, nine LED lamps could be lit. The work provides an effective approach to enhancing the piezoelectric effects of PVDF for low-power electronic loading of macromolecule polymers.

Piezoelectric enhanced photocatalytic properties of PVDF–ZnO/Cu nanofibers prepared by electrospinning technique

ABSTRACT Piezoelectric-assisted photocatalysis technology is one of the efficient ways to achieve enhancement in photocatalytic performance by facilitating the separation of photoinduced electron and holes via internal field initiated via piezoelectricity. Herein, bi-piezoelectric integrated effect was generated by the combination of piezoelectric semiconductor photocatalyst ZnO/Cu and piezoelectric polymer polyvinylidene fluoride (PVDF). Firstly, ZnO/Cu nanoparticles were prepared by facile co-precipitation method. Then, nanoparticles (at 10–30 wt%) were loaded in PVDF for fabricating nanofibers by electrospinning technique. All PVDF–ZnO/Cu nanofibers were characterized by XRD, FE-SEM, FTIR, XAS, and UV–Vis DRS. The structural study indicates that the β- and α-phase PVDF is observed in all the prepared nanofibers. XANES technique confirms the oxidation state of 2+ for Zn and Cu ions in both nanoparticles and nanofibers. Furthermore, under the synergy action of ultrasonic and visible light irradiation, PVDF–ZnO/Cu nanofibers exhibit superior piezo-photocatalytic degradation of rhodamine B dye when compared with single light or mechanical excitation. Effects of ZnO/Cu concentration on optical, piezoelectric, and photocatalytic properties are discussed.

Development of PVDF nanocomposite with single-walled carbon nanotubes (SWCNT) and boron nitride nanotubes (BNNT) for soft morphing actuator

Soft morphing actuators can deliver a range of displacements whilst being flexible and lightweight, making them advantageous over traditional mechanical actuators. Piezoelectric polymer polyvinylidene fluoride (PVDF) is combined with nanofillers to achieve superior soft actuator with the nanocomposite than with solely the polymer. This paper investigates and compares the distinctive effects of 1D nanofillers: single-walled carbon nanotubes (SWCNTs) and boron nitride nanotubes (BNNTs), through the promotion of crystal structures and polar β crystals of PVDF, and consequently its actuation ability. Results showed that 80 µm thick 2 wt.% SWCNT/PVDF clamped at both ends with a 10 mm span achieved a high deflection per applied electric field of 414 µm (V mm−1)−1 and deflection of 570 µm. This was due to a combination of fabrication method, physical geometry, and large surface area of SWCNTs leading to enhanced degree of crystallinity, β crystals, dielectric constant, and conductivity. The increase in both overall crystal formation and targeted β crystals lead to a high total β crystal content of 35%, and the conductivity lead to a low applied electric field of 1.3 V mm−1. BNNT/PVDF was able to undergo electric poling due to its insulating nature. BNNT/PVDF achieved a deflection magnitude per applied electric field of 2.9 µm (V mm−1)−1, due to a much higher electric field (90–150 V mm−1). This corresponded to a deflection magnitude of 260 µm, which was a 520% increase from only stretched BNNT/PVDF samples. Both nanocomposites displayed large scale actuation that is greater than the 70 µm deflection (0.9 µm (V mm−1)−1) observed for pure PVDF of same geometry and setup.

Analytical and experimental study of a clamped-clamped, bistable buckled beam low-frequency PVDF vibration energy harvester

Vibration-based energy harvesting devices have drawn interest as a potential low-maintenance power source for a variety of applications, such as for systems involving distributed networks of remote sensors. In this work, an energy harvesting system is considered that is based on bistable, buckled beams and the flexible piezoelectric polymer polyvinylidene fluoride (PVDF). The stability and dynamic response of the structure under vibration loading is modeled, and the resulting output voltage is analytically predicted. Modeling outputs are compared with experimental results for driving frequencies below 30 Hz, the range for many common vibration energy harvesting environments. The modeling approach used in this work is based on coupled electrical-mechanical equations of motion for a geometrically nonlinear Euler-Bernoulli piezoelectric beam that were developed via Hamilton's principle. A component sectioning procedure was used in conjunction with implementation of matching conditions at the boundaries to solve for the nonlinear static and linearized dynamic structural equations. These gave both the buckling and dynamic shape functions, which were used as a basis for finding the device nonlinear dynamic response. Several parameters including vibrational motion, output voltage, and frequency response were analyzed both theoretically and experimentally under different driving conditions. Good agreement was found between the developed model and the experiments, particularly with respect to predicted regimes of behavior and power output. The results suggest that the proposed modeling approach could be successfully implemented in the design and analysis of other multi-component piezoelectric-based energy harvesting systems.

Contactless, Battery-free, and Stretchable Wearable for Continuous Recording of Seismocardiograms

Seismocardiography (SCG) is the technique to measure microscale vibrations of the chest, which is closely related to the mechanical activity of the heart. To date, only a few studies have reported technical solutions to remotely measure SCG signals with soft electronics using stretchable, piezoelectric thin films. In this study, however, we demonstrate a contactless wearable patch using a 28-μm-thick foil of the piezoelectric polymer polyvinylidene fluoride. As a technical advancement, we utilize near-field communication (NFC) technology to power the patch and to record the SCG data wirelessly. A separated electrocardiogram (ECG) is used as a reference. Our results show expected waveforms of the recorded SCG signals with good signal-to-noise ratios and a close correlation between SCG and ECG recordings. The SCG technique adds an additional tool for cardiac monitoring, which is tightly associated with an ECG. The SCG method could be combined with other techniques in wearable on-skin electronics with multiple functionality for advanced cardiovascular monitoring.

PVDF Sensor Foils Employed to Measure Shear Stress and Temperature of Friction Welding

Friction welding is a popular process for joining metal and polymer work pieces by rubbing them against each other. This way, friction heat is generated in a zone of the faying surfaces, thinner than 1 mm. After cooling down, the heated surfaces establish a tight and strong bond. To improve this joining process, a method is desirable allowing measuring generated temperature and shear stress in the zone between the joining work pieces. Unfortunately, this is a very difficult task because the welding zone cannot be accessed with a sensor without significantly altering the process and thereby the desired measurement results. This paper describes how shear stress and temperature change generated by rubbing polymer pieces in a friction welding machine have been measured between the faying surfaces by employing sensor foils from the piezoelectric and pyroelectric polymer polyvinylidene fluoride (PVDF). This way, heating and cooling rates, pressure rise of the pneumatic system, frequency rise of the starting machine, the duration of starting and stopping, the damping of the vibrations after the drive was stopped, and the stress generated by the pullback of the machine head have been measured. A careful characterization of the sensor was necessary to enable distinguishing the measured voltage due to straining, shearing and temperature change.

Dual light-activated microfluidic pumps based on an optopiezoelectric composite

In this paper, a new type of microfluidic pump that can be activated and controlled by a masked light source is presented. The actuation of this micropump is based on an optopiezoelectric composite. This composite is constructed by having one of the electrodes of a piezoelectric PVDF (polyvinylidene fluoride) polymer replaced by a layer of TiOPc (titanyl phthalocyanine) photoconductive coating and an ITO (indium-tin-oxide) transparent electrode. This layer of photoconductive electrode provides the capability to activate multiple locations of this optopiezoelectric composite independently using a masked light source and a single voltage source. To verify the feasibility of this concept, dual light-activated microfluidic pumps based on this optopiezoelectric composite are implemented and studied. Experimental results verify that two microfluidic pumps can be created by one optopiezoelectric composite and that each pump can be optically turned on and off independently or be turned on simultaneously. These results suggest that integrating an optopiezoelectric composite into a lab-on-a-chip system can reduce the size and the number of driving units significantly, since every operation can be done optically and only one driving source is needed. The equivalent circuit, design, and implementation of dual light-activated optopiezoelectric micropumps are discussed in this paper.

Polymeric Sensor Fibers Based on a Piezoelectric Polymer and Metal Alloy/Carbon Nanotube/Polymer Composite for Structural Health Monitoring

Sensor fibers can be used for structural health monitoring in multiple environmental applications. Possible areas of applications are in geotextiles for monitoring the status of the reinforcement or in wind energy plants to monitor the load on wind blades. In this paper, a new type of sensor fiber based on a piezoelectric polymer (polyvinylidene fluoride) and a composite material made of a thermoplastic polymer, a low melting point metal alloy and carbon nanotubes (CNT) is presented. The piezoelectric polymer generates a signal when a load is applied if it is processed in the right way. Here, the formation of the piezoelectric crystalline structures will be presented. The conductive compound transmits the signal to measurement equipment. While CNT form a conductive network in the polymer, the metal alloy acts as a coating for the nanotubes and increases the electrical conductivity (100 S/m) by two orders of magnitude compared to pure CNT nanocomposites (approx. 1 S/m). The increased conductivity allows the transmission of the signals over larger distances, making the material favourable for large scale applications like wind blades.

Ultrasound-mediated piezoelectric differentiation of neuron-like PC12 cells on PVDF membranes

Electrical and/or electromechanical stimulation has been shown to play a significant role in regenerating various functionalities in soft tissues, such as tendons, muscles, and nerves. In this work, we investigate the piezoelectric polymer polyvinylidene fluoride (PVDF) as a potential substrate for wireless neuronal differentiation. Piezoelectric PVDF enables generation of electrical charges on its surface upon acoustic stimulation, inducing neuritogenesis of PC12 cells. We demonstrate that the effect of pure piezoelectric stimulation on neurite generation in PC12 cells is comparable to the ones induced by neuronal growth factor (NGF). In inhibitor experiments, our results indicate that dynamic stimulation of PVDF by ultrasonic (US) waves activates calcium channels, thus inducing the generation of neurites via a cyclic adenosine monophosphate (cAMP)-dependent pathway. This mechanism is independent from the well-studied NGF induced mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) pathway. The use of US, in combination with piezoelectric polymers, is advantageous since focused power transmission can occur deep into biological tissues, which holds great promise for the development of non-invasive neuroregenerative devices.

Development of a Wearable Controller for Gesture-Recognition-Based Applications Using Polyvinylidene Fluoride.

This paper reports on a wearable gesture-based controller fabricated using the sensing capabilities of the flexible thin-film piezoelectric polymer polyvinylidene fluoride (PVDF) which is shown to repeatedly and accurately discern, in real time, between right and left hand gestures. The PVDF is affixed to a compression sleeve worn on the forearm to create a wearable device that is flexible, adaptable, and highly shape conforming. Forearm muscle movements, which drive hand motions, are detected by the PVDF which outputs its voltage signal to a developed microcontroller-based board and processed by an artificial neural network that was trained to recognize the generated voltage profile of right and left hand gestures. The PVDF has been spatially shaded (etched) in such a way as to increase sensitivity to expected deformations caused by the specific muscles employed in making the targeted right and left gestures. The device proves to be exceptionally accurate both when positioned as intended and when rotated and translated on the forearm.

Thermal energy harvesting by piezoelectric PVDF polymer coupled with shape memory alloy

A novel flexible composite thermal energy harvester is presented, which couples pyroelectric and piezoelectric effects of polyvinylidene fluoride (PVDF) with shape memory effect of TiNiCu alloy. The harvester combines superior flexibility of PVDF with large temperature-induced strain of the shape memory alloy to harvest small and quasi-static temperature variations. The post-stamp size harvester (27.5mm3) achieved an energy density of 0.41mJ/cm3 per event of temperature variation of 20°C. When reaching 70°C the harvester, consisting of a stack of four PVDF, powered a wireless node instantaneously without any storage unit. The use of PVDF quadruples the energy output, compared to previously reported PZT-based composites.

Classification and Simulation Method for Piezoelectric PVDF Sensors

The piezoelectric polymer Polyvinylidene fluoride (PVDF) holds the potential to be the core material of novel structure-borne sound sensors not only in research but also in industrial applications. This paper will give an overview of possibilities when PVDF is useful and when PVDF reaches its limits of applicability. To do so, a state of the art about current applications of PVDF will be given. Furthermore, the consecutive equations and an experimental setup for the classification of the piezoelectric constants and Young's moduli over frequency and temperature will be presented. A simplified FE simulation method will also be shown to model PVDF film sensors by computer aided design.

Electrospun polyvinylidene fluoride nanofibers by bubble electrospinning technique

This work reports, for the first time, the electrospinning of the piezoelectric and ferroelectric polymer polyvinylidene fluoride (PVDF) by means of the bubble electrospinning technique. We focus our study in the effect of different applied voltages on the morphological and crystalline features of the PVDF bubble-electrospun nanofibers. The crystallinity of PVDF nanofibers that were obtained by this process was higher than that observed in traditionally synthesized PDVF powders. Is important to highlight that production rate of the obtained PVDF nanofibers was higher (13.93mL/h) than that of the reported traditional electrospinning (1–5mL/h).

Flexible Tactile Sensors Using Screen-Printed P(VDF-TrFE) and MWCNT/PDMS Composites

This paper presents and compares two different types of screen-printed flexible and conformable pressure sensors arrays. In both variants, the flexible pressure sensors are in the form of segmental arrays of parallel plate structure—sandwiching the piezoelectric polymer polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] between two printed metal layers of silver (Ag) in one case and the piezoresistive [multiwall carbon nanotube (MWCNT) mixed with poly(dimethylsiloxane (PDMS)] layer in the other. Each sensor module consists of $4 \times 4$ sensors array with 1-mm $\times 1$ -mm sensitive area of each sensor. The screen-printed piezoelectric sensors array exploits the change in polarization level of P(VDF-TrFE) to detect dynamic tactile parameter such as contact force. Similarly, the piezoresistive sensors array exploits the change in resistance of the bulk printed layer of MWCNT/PDMS composite. The two variants are compared on the basis of fabrication by printing on plastic substrate, ease of processing and handling of the materials, compatibility of the dissimilar materials in multilayers structure, adhesion, and finally according to the response to the normal compressive forces. The foldable pressure sensors arrays are completely realized using screen-printing technology and are targeted toward realizing low-cost electronic skin.

Photopiezoelectric Composites of Azobenzene‐Functionalized Polyimides and Polyvinylidene Fluoride

Light is a readily available and sustainable energy source. Transduction of light into mechanical work or electricity in functional materials, composites, or systems has other potential advantages derived from the ability to remotely, spatially, and temporally control triggering by light. Toward this end, this work examines photoinduced piezoelectric (photopiezoelectric) effects in laminate composites prepared from photoresponsive polymeric materials and the piezoelectric polymer polyvinylidene fluoride (PVDF). In the geometry studied here, photopiezoelectric conversion is shown to strongly depend on the photomechanical properties inherent to the azobenzene-functionalized polyimides. Based on prior examinations of photomechanical effects in azobenzene-functionalized polyimides, this investigation focuses on amorphous materials and systematically varies the concentration of azobenzene in the copolymers. The baseline photomechanical response of the set of polyimides is characterized in cantilever deflection experiments. To improve the photomechanical response of the materials and enhance the electrical conversion, the polyimides are drawn to increase the magnitude of the deflection as well as photogenerated stress. In laminate composites, the photomechanical response of the materials in sequenced light exposure is shown to transduce light energy into electrical energy. The frequency of the photopiezoelectric response of the composite can match the frequency of the sequenced light exposing the films.

Study on electromechanical characterization of piezoelectric polymer PVDF in low-frequency band

Polyvinylidene fluoride (PVDF), a piezoelectric polymer material, is well known as one of the best smart materials to be used for tactile sensors in robots for its good performance. It has been used in many applications including sensors, actuators and surface acoustic wave (SAW) devices. This paper presents an experimental setup and experimental procedures for studying the electromechanical characterization of piezoelectric polymer films, by which the electromechanical characterization of the PVDF films under quasi-static loads and dynamic loads in a wide range of frequency can be researched. Through quasi-static tests, the stress–strain relationships of PVDF films in different directions were obtained. Furthermore, the viscoelastic and piezoelectric properties of PVDF films were analyzed based on the measurement results of dynamic tests under low frequency from 5 Hz to 200 Hz, and some suggestions of the applications of PVDF piezoelectric films in robot tactile sensor are presented.