Poly Vinylidene Fluoride-trifluoroethylene Research Articles

Comprehensive characterization of PVDF-TrFE thin films for microelectromechanical system applications

This paper presents a comprehensive characterization of a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) thin film with 75/25 molar ratio for piezoelectric MEMS applications. PVDF-TrFE film was deposited on a silicon substrate using spin coating, and electrodes were formed using sputtering. Dielectric constant and dielectric loss factor were measured at different frequencies. Frequency and temperature dependence of the ferroelectric response was examined to investigate required poling conditions and maximum operating temperature. The lower limit for the coercive field was measured as 55 V/μm at room temperature. Coercive field decreased with temperature with a slope of −0.1 V/μm K, and ferroelectric to paraelectric transition occurred between 100 and 108 °C. Piezoelectric displacement measurements were performed using an atomic force microscope based method. Average value of the effective piezoelectric d33 coefficient was measured as −23.9 pm/V. No degradation was observed in this value after 2 × 105 unipolar excitation cycles. On the other hand, significant fatigue was observed in the piezoelectric response due to polarization switching; 1.8 × 105 cycles caused an average reduction of 33% in the effective d33. Presented data corroborates with the previous studies in the literature and can be used in the design of PVDF-TrFE based MEMS devices utilizing its dielectric, ferroelectric, and piezoelectric properties.

High‐Performance Piezoelectric Nanogenerators with Imprinted P(VDF‐TrFE)/BaTiO3 Nanocomposite Micropillars for Self‐Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high-performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE))/barium titanate (BaTiO3 ) for energy harvesting and highly sensitive self-powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF-TrFE)/BaTiO3 nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm-2 , which an enhancement by a factor of 7.3 relatives to the pristine P(VDF-TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF-TrFE)/BaTiO3 nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self-powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.

Ferroelectric surfaces for cell release

Adherent cells cultured in vitro must usually, at some point, be detached from the culture substrate. Presently, the most common method of achieving detachment is through enzymatic treatment which breaks the adhesion points of the cells to the surface. This comes with the drawback of deteriorating the function and viability of the cells. Other methods that have previously been proposed include detachment of the cell substrate itself, which risks contaminating the cell sample, and changing the surface energy of the substrate through thermal changes, which yields low spatial resolution and risks damaging the cells if they are sensitive to temperature changes. Here cell culture substrates, based on thin films of the ferroelectric polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) co-polymer, are developed for electroactive control of cell adhesion and enzyme-free detachment of cells. Fibroblasts cultured on the substrates are detached through changing the direction of polarization of the ferroelectric substrate. The method does not affect subsequent adhesion and viability of reseeded cells.

Liquid-phase tuning of porous PVDF-TrFE film on flexible substrate for energy harvesting

Emerging wearable and implantable biomedical energy harvesting devices demand efficient power conversion, flexible structures, and lightweight construction. This paper presents Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) micro-porous structures, which can be tuned to specific mechanical flexibilities and optimized for piezoelectric power conversion. Specifically, the water vapor phase separation method was developed to control microstructure formation, pore diameter, porosity, and mechanical flexibility. Furthermore, we investigated the effects of the piezoelectric layer to supporting layer Young's modulus ratio, through using both analytical calculation and experimentation. Both structure flexibility and stress-induced voltage were considered in the analyses. Specification of electromechanical coupling efficiency, made possible by carefully designed three-dimensional porous structures, was shown to increase the power output by five-fold relative to uncoupled structures. Therefore, flexible PVDF-TrFE films with tunable microstructures, paired with substrates of different rigidities, provide highly efficient designs of compact piezoelectric energy generating devices.

Investigation of nanoyarn preparation by modified electrospinning setup.

Higher ordered structures of nanofibers, including nanofiber-based yarns and cables, have a variety of potential applications, including wearable health monitoring systems, artificial tendons, and medical sutures. In this study, twisted assemblies of polyacrylonitrile (PAN), polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), and polycaprolactone (PCL) nanofibers were fabricated via a modified electrospinning setup, consisting of a rotating cone-shaped copper collector, two syringe pumps, and two high voltage power supplies. The fiber diameters and twist angles varied as a function of the rotary speed of the collector. Mechanical testing of the yarns revealed that PVDF-TrFe and PCL yarns have a higher strain-to-failure than PAN yarns, reaching 307% for PCL nanoyarns. For the first time, the porosity of nanofiber yarns was studied as a function of twist angle, showing that PAN nanoyarns are more porous than PCL yarns.

Improved dielectric properties and energy storage density of poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) composite films with aromatic polythiourea

Energy storage materials are crucial for efficient utilization of electricity in modern electric power supply and renewable energy systems. Film capacitors are promising technologies for electrical energy storage for their high power densities and charge–discharge rate, yet they are limited by their relatively low energy densities. The addition of high-k inorganic particles can lead to high dielectric constant, but at the expense of low breakdown strength and low energy efficiency, which limits their practical applications at high electric fields. In this work, we report all-organic dielectric films based on poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) (PVDF–TrFE–CTFE) terpolymer and aromatic polythiourea (ArPTU) and having enhanced energy density, energy storage efficiency, and breakdown field. Aromatic polythiourea was prepared by a conventional polycondensation method. The ArPTU/PVDF–TrFE–CTFE composite films were fabricated by solution-blending followed by hot pressing. The composite films have lower dielectric loss and higher breakdown field than the PVDF–TrFE–CTFE matrix. More importantly, the blend films also show improved released energy density and reduced loss at high fields. For ArPTU/PVDF–TrFE–CTFE (15/85) composite film, the maximum released energy density is 19.2 J/cm3 at 700 MV/m with an efficiency of 85%. The improved energy density and reduced energy loss are related to the increase in electric resistivity and structural changes. The findings of this research could provide a simple and scalable approach to produce compact and flexible high energy density materials for energy storage devices.

Enhanced noradrenergic axon regeneration into schwann cell-filled PVDF-TrFE conduits after complete spinal cord transection.

Schwann cell (SC) transplantation has been utilized for spinal cord repair and demonstrated to be a promising therapeutic strategy. In this study, we investigated the feasibility of combining SC transplantation with novel conduits to bridge the completely transected adult rat spinal cord. This is the first and initial study to evaluate the potential of using a fibrous piezoelectric polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) conduit with SCs for spinal cord repair. PVDF-TrFE has been shown to enhance neurite growth in vitro and peripheral nerve repair in vivo. In this study, SCs adhered and proliferated when seeded onto PVDF-TrFE scaffolds in vitro. SCs and PVDF-TrFE conduits, consisting of random or aligned fibrous inner walls, were transplanted into transected rat spinal cords for 3 weeks to examine early repair. Glial fibrillary acidic protein (GFAP)+ astrocyte processes and GFP (green fluorescent protein)-SCs were interdigitated at both rostral and caudal spinal cord/SC transplant interfaces in both types of conduits, indicative of permissivity to axon growth. More noradrenergic/DβH+ (dopamine-beta-hydroxylase) brainstem axons regenerated across the transplant when greater numbers of GFAP+ astrocyte processes were present. Aligned conduits promoted extension of DβH+ axons and GFAP+ processes farther into the transplant than random conduits. Sensory CGRP+ (calcitonin gene-related peptide) axons were present at the caudal interface. Blood vessels formed throughout the transplant in both conduits. This study demonstrates that PVDF-TrFE conduits harboring SCs are promising for spinal cord repair and deserve further investigation. Biotechnol. Bioeng. 2017;114: 444-456. © 2016 Wiley Periodicals, Inc.

Enhanced Photovoltaic Performance of Perovskite Solar Cells Using Polymer P(VDF-TrFE) as a Processed Additive

It is known that CH3NH3PbI3 perovskite films with high crystallization and controlled morphology always show enhanced power conversion efficiency. Here we incorporate a small amount of polyvinylidene fluoride–trifluoroethylene polymer P(VDF-TrFE) into PbI2 solution to control the crystallinity and morphology of perovskite layer in a two-step deposition process. Our results show that the P(VDF-TrFE) bridges the grain boundaries and also enhances the crystallinity of the perovskite layer significantly. By adjusting P(VDF-TrFE) concentration, the fabricated perovskite solar cells show improved average power conversion efficiency from 9.57 ± 0.25% to 12.54 ± 0.40% under a standard illumination of 100 milliwatts per square centimeter, which increases by nearly 31%. Thus, we demonstrate a new strategy to control the crystallinity and morphology of perovskite films by incorporating polymer into PbI2 film in a two-step deposition process. In addition, this method has been proven as an effective way to prepare hig...

Investigation of PVDF-TrFE composite with nanofillers for sensitivity improvement

Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) is a good candidate for wearable tactile sensing application, owing to its flexibility and easy processing. In this paper, we studied the effect of mixing silver nano-fillers with different morphologies into PVDF-TrFE to improve the extent of β phase crystallization and the piezoelectric performance. After blending, the piezoelectric responding voltage of the composite was increased by a factor of more than three. This improvement results from the PVDF-TrFE chain arranges differently onto the nano-fillers with different morphologies, thus affects the crystallization.

The effect of PVDF-TrFE scaffolds on stem cell derived cardiovascular cells.

Recently, electrospun polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) scaffolds have been developed for tissue engineering applications. These materials have piezoelectric activity, wherein they can generate electric charge with minute mechanical deformations. Since the myocardium is an electroactive tissue, the unique feature of a piezoelectric scaffold is attractive for cardiovascular tissue engineering applications. In this study, we examined the cytocompatibility and function of pluripotent stem cell derived cardiovascular cells including mouse embryonic stem cell-derived cardiomyocytes (mES-CM) and endothelial cells (mES-EC) on PVDF-TrFE scaffolds. MES-CM and mES-EC adhered well to PVDF-TrFE and became highly aligned along the fibers. When cultured on scaffolds, mES-CM spontaneously contracted, exhibited well-registered sarcomeres and expressed classic cardiac specific markers such as myosin heavy chain, cardiac troponin T, and connexin43. Moreover, mES-CM cultured on PVDF-TrFE scaffolds responded to exogenous electrical pacing and exhibited intracellular calcium handling behavior similar to that of mES-CM cultured in 2D. Similar to cardiomyocytes, mES-EC also demonstrated high viability and maintained a mature phenotype through uptake of low-density lipoprotein and expression of classic endothelial cell markers including platelet endothelial cell adhesion molecule, endothelial nitric oxide synthase, and the arterial specific marker, Notch-1. This study demonstrates the feasibility of PVDF-TrFE scaffold as a candidate material for developing engineered cardiovascular tissues utilizing stem cell-derived cells. Biotechnol. Bioeng. 2016;113: 1577-1585. © 2015 Wiley Periodicals, Inc.

Electrodeposition of Piezoelectric Polymer Ultrasonic Transceivers for On-Chip Antibiotic Biosensors

In this study, on-chip piezoelectric polymer ultrasonic transceivers based on electrodeposition of polyvinylidene fluoride–trifluoroethylene (PVDF–TrFE) copolymer were developed and their use for ultrasensitive detection of antibiotic drugs was demonstrated. The transceivers, including receivers and transmitters, were electrodeposited on prepatterned gold electrodes in a single step at room temperature. PVDF–TrFE layers were deposited and poled simultaneously because of the polarization of dipoles in the electric field. A couple of PVDF–TrFE droplets were used to fabricate ultrasonic transducers through a local electrodeposition process, which required only 10 min. The fabricated ultrasonic transducers had a diameter of 680 μm and were integrated with a microfluidic channel. The measured transduction efficiency of the developed transceivers was 29.03%. These developed biosensors have been successfully applied for the detection of doxycycline, which is frequently used in animals, and a detection limit of 50 ppb was achieved. Furthermore, a simple, economical, and easy-to-use technique was developed for fabricating piezoelectric polymer devices on a small scale. The developed on-chip ultrasonic transceivers, which exhibited high ultrasonic performance in a microfluidic channel, have potential for use in ultrasensitive detection of proteins, DNA, and food antibiotics drugs.

Ultra-Thin Silicon based Piezoelectric Capacitive Tactile Sensor

This paper presents an ultra-thin bendable silicon based tactile sensor, in a piezoelectric capacitor configuration, realized by wet anisotropic etching as post-processing steps. The device is fabricated over bulk silicon, which is thinned down to 35 μm from an original thickness of 636 μm. Dicing of thin membrane is achieved by low cost novel technique of Dicing before Etching. The piezoelectric capacitor is composed of polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), which present an attractive avenue for tactile sensing as they respond to dynamic contact events (which is critical for robotic tasks), easy to fabricate at low cost and are inherently flexible. The sensor exhibits enhanced piezoelectric properties, thanks to the optimization of the poling procedure. The sensor capacitive behaviour is confirmed using impedance analysis and the electro-mechanical characterization is done using TIRA shaker setup.

Non-volatile polarization switch of magnetic domain wall velocity

Controlled propagation speed of individual magnetic domains in metal channels at the room temperature is obtained via the non-volatile field effect associated with the switchable polarization of P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) ferroelectric polymer. Polarization domains directly written using conducting atomic force microscope probe locally accelerate/decelerate the magnetic domains in the 0.6 nm thick Co film. The change of the magnetic domain wall velocity is consistent with the magnetic anisotropy energy modulation through the polarization upward/downward orientation. Excellent retention is observed. The demonstrated local non-destructive and reversible change of magnetic properties via rewritable patterning of ferroelectric domains could be attractive for exploring the ultimate limit of miniaturization in devices based on ferromagnetic/ferroelectric bilayers.

MEMS Scale PVDF-TrFE-Based Piezoelectric Energy Harvesters

This paper presents the design, the fabrication, and the performance characterization of microelectromechanical systems (MEMS) scale cantilever-type piezoelectric energy harvesters (PEHs) that utilize the piezoelectric polymer polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE). Ranges are determined for device dimensions according to the calculations based on mathematical models. Designed devices were fabricated using standard MEMS fabrication techniques. Electrodes were formed with sputtered Al and Ti/Al thin films, and a 1.3- $\mu \text{m}$ -thick PVDF-TrFE film was deposited using spin coating. Cantilevers were suspended using a two-step process: backside DRIE to perform the bulk etch, followed by XeF2 gaseous etch for the final release. Remnant polarization and coercive field of the fabricated devices were measured as $6.1~\mu \text{C}/\text{cm}^2$ and 74.9 V/ $\mu \text{m}$ , respectively. Piezoelectric performances were evaluated by a press-and-release type of measurement. For these measurements, custom-made probe tips attached to micropositioners were used. Based on the experimental results, maximum power output was calculated as 35.1 pW for a peak tip displacement of $500~\mu \text{m}$ from a $1200~\mu \text {m} \times 300 ~\mu \text{m}$ cantilever, which corresponds to a power output density of 97.5 pW/mm2. The proposed method has the potential to create the PEHs that are monolithically integrated with complementary metal-oxide–semiconductor circuits and lead to self-sustained low power electronics. [2015-0117]

Inkjet printing of high molecular weight PVDF-TrFE for flexible electronics

Introduction of the revolutionary drop-on-demand (DoD) inkjet printing technique for microelectronics allows the use of flexible substrate, organic and inorganic materials, and low-cost volume fabrication. However, inks of different functional materials for varieties of applications are still under development. Polyvinylidene fluoride–trifluoroethylene (PVDF-TrFE), a potential candidate for mechanical and acoustic sensors, actuators, energy harvesting and nonvolatile memory applications, is a copolymer that exhibits piezo-, pyro- and ferro-electric properties. During this work, inkjet-printed films using high molecular weight PVDF-TrFE were developed and characterized to investigate their morphology and crystallinity. Modified waveform and very low jetting frequency have been used to accommodate relaxation time of the polymeric ink during jetting. Crystallographic studies confirm the presence of a β-phase, which exhibits spontaneous polarization per unit cell.

Surface Shearing Effects on Langmuir–Blodgett Thin Films of P(VDF-TrFE) Ferroelectric Surface

Polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) copolymers, also called Nobel polymers due to their ferroelectric, piezoelectric, and pyroelectric properties, possess non-lineal optical properties and low acoustic impedance that pair with water and living tissue (i.e. are biocompatible). These qualities make them promising for multiple electronic applications. In this paper we explore the effects of applying a shearing force on copolymer of Polyvinylidene Fluoride with Trifluoroethylene (P(VDF-TrFE) thin film has been studied. A shearing technique was used to induce stress on the film, which produced an improvement in crystallization and grain size.

Flexible Two-ply Piezoelectric Yarn Energy Harvester

We developed a flexible two-ply piezoelectric yarn-type generator using an electrospun polyvinylidenefluorideco- trifluoroethylene (PVDF–TrFE) mat and a commercially available silver-coated nylon fiber. By rolling the silvercoated nylon fiber into the electrospun PVDF–TrFE mat as the inner electrode, the two-dimensional piezoelectric PVDF– TrFE mat was easily transformed into a one-dimensional fiber. Then silver-coated nylon fiber rolled in PVDF–TrFE was plied with another similar fiber to make a flexible two-ply piezoelectric yarn. The overall fabrication processes of the flexible two-ply piezoelectric yarn are simple and have a high application potential. The flexible two-ply piezoelectric yarn can generate up to 0.7 V in compression and 0.55 V in tension. The yarn retained the piezoelectric performance in various shapes, such as a sewn structure. In addition, the piezoelectric performance was sensitive to velocity and pressure. The flexible two-ply piezoelectric yarn has potential applications as a human motion sensor, as a building block of energy- harvesting textiles, and in self-powered biomedical applications. Keywords: Energy harvester, Flexible, Piezoelectric, Two-ply, Wearable, Yarn.

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.

High-performance flexible lead-free nanocomposite piezoelectric nanogenerator for biomechanical energy harvesting and storage

Environmentally friendly and flexible piezoelectric nanogenerators (PENGs) have attracted considerable interest for use in autonomous micro-/nano-systems, wearable electronics, and implantable biomedical devices. Herein, a flexible, lead-free, solution-processable and efficient PENG is demonstrated, based on a highly piezoelectric nanocomposite thin film of barium titanate nanoparticles (BT NPs) embedded into a highly crystalline polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE)) polymer for charge storage. The nanocomposite PENG (nc-PENG) with high loading of BT NPs up to 40wt% in the nanocomposite can produce output voltage as high as 9.8V and output power density of 13.5µW/cm2 under cyclic bending, comparable to the output of conventional inorganic polycrystalline lead zirconate titanate PENGs. The high performance of these nc-PENGs is primarily attributed to the very high effective piezoelectricity of the highly crystalline P(VDF-TrFE), strengthened by the BT NPs. The nc-PENG was also demonstrated to harvest biomechanical energy from simple body movements and store the generated electricity during mechanical and biomechanical motions in a rechargeable microbattery.

Sensitivity improvement of graphene/Al2O3/PVDF–TrFE stacked touch device through Al seed assisted dielectric scaling

The sensitivity of touch sensor using piezoelectric polymer/graphene stack has been drastically improved by scaling the thickness of dielectric on the graphene. The piezoelectric effect induced charges in graphene channel were increased from 0.6195 to 4.314μC/cm2 at 1kg press weight, which by enhancing the charge coupling between the PVDF–TrFE and graphene channel through the Al2O3 scaling from 30nm to 5nm.