Polyvinylidene Fluoride Thin Films Research Articles

Influences of post-heating treatment on crystalline phases of PVDF thin films prepared by atmospheric pressure plasma deposition

This paper systematically investigates the effects of the post-heating treatment on the structural characteristics of the polyvinylidene fluoride (PVDF) thin film that is deposited as the high-density thin films with nanoparticles by improving the sufficient nucleation of PVDF solution by atmospheric pressure plasma (APP) deposition system. The surface morphology of PVDF thin film was measured by using scanning electron microscopy (SEM), and structural characteristic of PVDF thin film was systematically investigated by X-ray diffraction (XRD) and Fourier transforms-infrared spectroscopy (FT-IR) with respect to different post-heating conditions in order to reduce the N,N-dimethylformamide (DMF) element and enhancing the crystalline phase of PVDF thin film. As the post-heating temperature was increased, the amount of bubble and bubble size were decreased. This means that the DMF solution is almost removed from the post-heated PVDF thin film, and the PVDF nanoparticles are clearly observed on the surface of PVDF thin film synthesized by APP deposition method. In FT-IR spectra, the peak intensity at 1669 cm−1 for -C = O by DMF solution highly decreases after post-heating treatment, and the crystalline phases of the PVDF thin film have mainly two phases (α and β phases), which indicates the peaks at 975 and 1402 cm−1 for α-phase and the peak at 1072 cm−1 for β-phase, respectively.

Cutting Forces Measurement for Milling Process by Using Working Tables with Integrated PVDF Thin-Film Sensors.

In the milling process, cutting forces contain key information about the machining process status in terms of workpiece quality and tool condition. On-line cutting force measurement is key for machining condition monitoring and machined surface quality assurance. This paper presents a novel instrumented working table with integrated polyvinylidene fluoride (PVDF) thin-film sensors, thus enabling the dynamic milling force measurement with compact structures. To achieve this, PVDF thin-film sensors are integrated into the working table to sense forces in different directions and the dedicated cutting force decoupling model is derived. A prototype instrumented working table is developed and validated. The validation demonstrates that profiles of the forces measured from the developed instrumented working table prototype and the dynamometer match well. Furthermore, the milling experiment results convey that the instrumented working table prototype could also identify the tool runout due to tool manufacturing or assembly errors, and the force signal spectrum analysis indicates that the developed working table can capture the tool passing frequency correctly, therefore, is suitable for the milling force measurement.

Tunable polarization components and electric field induced crystallization in polyvinylidenefluoride: A piezo polymer

Polyvinylidenefluoride (PVDF) a semicrystalline pieozoelectric polymer was synthesized with varying process conditions and its ferroelectric domain orientations were studied using piezoresponse force microscope (PFM). PVDF thin films fabricated using tape casting technique with precursor solutions of varying viscosities reveal that the polarization components transform from a dominant planar to an out‐of‐plane configuration with increase in viscosity. Interestingly the planar components possessed a head to head or tail to tail kind of paired domains separated by a distance of ~ 380‐400 nm. Electrostatic energy minimization of an electrically inhomogeneous system containing similar domain arrangements as the experiments shows that the head to head and tail to tail arrangements with a minimum separation distance are more favorable than head to tail arrangements of domains. With increment of applied field, the domains grew in size and shape indicating amorphous to crystalline transformation of PVDF films. Such transformation was evident from X‐ray diffraction studies performed in‐situ in the presence of an applied electric field.

UV‐Induced Ferroelectric Phase Transformation in PVDF Thin Films

AbstractThin films of polyvinylidene fluoride (PVDF) enable access to efficient hybrid devices that operate at low voltages. However, the preparation of thin films from solution typically yields nonferroelectric crystalline phases that require additional processing steps to transform the nonferroelectric phases to the more desirable ferroelectric polymorphs. Here, a rapid photonic annealing technique is reported that induces an α‐ to β‐phase transformation in PVDF thin films, opening up the opportunity to process the material via high‐throughput processing conditions such as roll‐to‐roll processing. This photonic annealing process uses a microsecond‐scale light pulse to transform the spin‐coated films into the desired ferroelectric PVDF phase. The structural evolution in these films is investigated under brief pulses of light, and it is shown that under optimal photonic annealing conditions, robust devices with a remnant polarization (P r) up to 5.4 µC cm−2 and a coercive field (E c) around 120 MV m−1 can be achieved.

"Pipe Organ" Inspired Air-Coupled Ultrasonic Transducers With Broader Bandwidth.

Piezoelectric micromachined ultrasonic transducers (PMUTs) are used to receive and transmit ultrasonic signals in industrial and biomedical applications. This type of transducer can be miniaturized and integrated with electronic systems since each element is small and the power requirements are low. The bandwidth of the PMUT may be narrow in some conventional designs; however, it is possible to apply modified structures to enhance this. This paper presents a methodology for improving the bandwidth of air-coupled PMUTs without sensitivity loss by connecting a number of resonating pipes of various lengths to a cavity. A prototype piezoelectric diaphragm ultrasonic transducer is presented to prove the theory. This novel device was fabricated by additive manufacturing (3-D printing), and consists of a polyvinylidene fluoride thin film over a stereolithography designed backplate. The backplate design is inspired by a pipe organ musical instrument, where the resonant frequency (pitch) of each pipe is mainly determined by its length. The -6-dB bandwidth of the "pipe organ" air-coupled transducer is 55.7% and 58.5% in transmitting and receiving modes, respectively, which is ~5 times wider than a custom-built standard device.

In situ synthesized electroactive and large dielectric BaF2/PVDF nanocomposite film for superior and highly durable self-charged hybrid photo-power cell

In present work, a simplistic, efficient and highly durable electroactive and high dielectric BaF2 nanoparticles (NPs) incorporated polyvinylidene fluoride (PVDF) thin film based Self-Charged Hybrid Photo-Power Cell (HPPC) has been designed which is able to self-charge under visible light illumination. The incorporation of NPs into the PVDF matrix has effectively enhanced the polar β crystallite nucleation (∼96%) and the dielectric value (∼2570) of the PVDF thin film. A composite dye film of TiO2 NPs, phenosafranine-polyvinyl pyrrolidone in the presence of H3PO4 is acted as the light absorbing and photoelectrons generating part in the HPPC. The photo-electrons are stored in the energy storage part made of the in situ synthesized BaF2 NPs embedded PVDF thin film. Our HPPC is able to generate a photovoltage ∼1.3 V within 65 s under exposure of visible light (∼110 mW/cm2) with superior energy storage efficiency ∼79%. The device has the ability of storing charge ∼1200 F/m2 with power density ∼18.7 W/m2 and charge density ∼1500 C/m2. Our light weighted self-charged power bank may be utilized as power supplier in portable electronic appliances.

Study of Impact Damage in PVA-ECC Beam under Low-Velocity Impact Loading Using Piezoceramic Transducers and PVDF Thin-Film Transducers.

Compared to conventional concrete, polyvinyl alcohol fiber reinforced engineering cementitious composite (PVA-ECC) offers high-strength, ductility, formability, and excellent fatigue resistance. However, impact-induced structural damage is a major concern and has not been previously characterized in PVA-ECC structures. We investigate the damage of PVA-ECC beams under low-velocity impact loading. A series of ball-drop impact tests were performed at different drop weights and heights to simulate various impact energies. The impact results of PVA-ECC beams were compared with mortar beams. A combination of polyvinylidene fluoride (PVDF) thin-film sensors and piezoceramic-based smart aggregate were used for impact monitoring, which included impact initiation and crack evolution. Short-time Fourier transform (STFT) of the signal received by PVDF thin-film sensors was performed to identify impact events, while active-sensing approach was utilized to detect impact-induced crack evolution by the attenuation of a propagated guided wave. Wavelet packet-based energy analysis was performed to quantify failure development under repeated impact tests.

Piezoelectric polymer thin films with architected cuts

Abstract

Ultrasonic tactile sensor integrated with TFT array for force feedback and shape recognition

In this study, we propose an ultrasonic tactile sensor for real time contact force measurements and high-resolution shape recognition to enable safe and reliable robotic grasping of objects that may vary in compliance or texture. The sensing mechanism utilizes piezoelectric transduction where pulsed alternating voltage signals are applied to a polyvinylidene fluoride (PVDF) thin film, which generates pulses of ultrasound waves that travel upwards through the sensor components to the object contact interface. These waves are reflected back onto a receiver PVDF thin film that produces a localized voltage output, which is detected by the TFT (Thin-Film Transistor) array layer and converted into a two-dimensional grayscale image after signal processing. The ability of the tactile sensor to detect contact forces can be attributed to the sensor surface having a thin compliant polymer layer with a microstructure array. When the sensor contacts objects, the microstructures act as force concentrators, resulting in the localized deformation of the polymer layer that can be observed by the proposed ultrasonic imaging technique with an observed linear response to normal static forces in the range of 1–6 N. Furthermore, the shape sensing resolution and force detection range of the tactile sensor can be tuned by varying the number of microstructures in the array and the utilization of polymers with varying hardness, respectively.

Effects of Gamma Irradiation on Polyvinylidene Fluoride Thin Films

Polyvinylidene fluoride thin films were synthesized by Sol-Gel method with spin rate of 3000 rpm for 30 sec on ITO glass substrates and were annealed at 170 C. The films were irradiated by Gamma radiation with different doses (10, 30, 40 and 50 kGy). XRD and FTIR spectra have been obtained to identify the presence of α / β phases. Mean crystallite size was calculated by Scherer’s equation. Different vibrational bands were identified and percentage of β phase was determined by FTIR analysis. Optical properties like band gap, refractive index, optical activation energy have been determined. Surface morphology and compositions of pristine and gamma irradiated PVDF thin films were confirmed respectively, by SEM and Energy dispersive X-ray analysis. The comparison of the structural and optical optical properties of pristine PVDF polymer film has been made with those of the Gamma irradiated films.

Tactile-Sensing Based on Flexible PVDF Nanofibers via Electrospinning: A Review.

The flexible tactile sensor has attracted widespread attention because of its great flexibility, high sensitivity, and large workable range. It can be integrated into clothing, electronic skin, or mounted on to human skin. Various nanostructured materials and nanocomposites with high flexibility and electrical performance have been widely utilized as functional materials in flexible tactile sensors. Polymer nanomaterials, representing the most promising materials, especially polyvinylidene fluoride (PVDF), PVDF co-polymer and their nanocomposites with ultra-sensitivity, high deformability, outstanding chemical resistance, high thermal stability and low permittivity, can meet the flexibility requirements for dynamic tactile sensing in wearable electronics. Electrospinning has been recognized as an excellent straightforward and versatile technique for preparing nanofiber materials. This review will present a brief overview of the recent advances in PVDF nanofibers by electrospinning for flexible tactile sensor applications. PVDF, PVDF co-polymers and their nanocomposites have been successfully formed as ultrafine nanofibers, even as randomly oriented PVDF nanofibers by electrospinning. These nanofibers used as the functional layers in flexible tactile sensors have been reviewed briefly in this paper. The β-phase content, which is the strongest polar moment contributing to piezoelectric properties among all the crystalline phases of PVDF, can be improved by adjusting the technical parameters in electrospun PVDF process. The piezoelectric properties and the sensibility for the pressure sensor are improved greatly when the PVDF fibers become more oriented. The tactile performance of PVDF composite nanofibers can be further promoted by doping with nanofillers and nanoclay. Electrospun P(VDF-TrFE) nanofiber mats used for the 3D pressure sensor achieved excellent sensitivity, even at 0.1 Pa. The most significant enhancement is that the aligned electrospun core-shell P(VDF-TrFE) nanofibers exhibited almost 40 times higher sensitivity than that of pressure sensor based on thin-film PVDF.

Sensor Piezoeléctrico con Geometría Lineal para Tomografía Optoacústica: Implementación y Caracterización Eléctrica

En este trabajo se presenta la implementación y caracterización eléctrica de un sensor polimérico piezoléctrico de banda ancha con geometría lineal, basado en una película delgada de fluoruro de polivinilideno. Se midió la impedancia eléctrica del sensor en función de la frecuencia, encontrándose que el polímero prácticamente no fue alterado por el proceso de fabricación del sensor. Además, se estudió la respuesta en frecuencia del sensor con un amplificador de transimpedancia, observándose una marcada reducción del ancho de banda del sistema debida a la elevada capacitancia del dispositivo.

Parametric modeling of wideband piezoelectric polymer sensors: Design for optoacoustic applications.

In this work, we present a three-dimensional model for the design of wideband piezoelectric polymer sensors which includes the geometry and the properties of the transducer materials. The model uses FFT and numerical integration techniques in an explicit, semi-analytical approach. To validate the model, we made electrical and mechanical measurements on homemade sensors for optoacoustic applications. Each device was implemented using a polyvinylidene fluoride thin film piezoelectric polymer with a thickness of 25 μm. The sensors had detection areas in the range between 0.5 mm2 and 35 mm2 and were excited by acoustic pressure pulses of 5 ns (FWHM) from a source with a diameter around 10 μm. The experimental data obtained from the measurements agree well with the model results. We discuss the relative importance of the sensor design parameters for optoacoustic applications and we provide guidelines for the optimization of devices.

Bipolar resistive switching in PVDF and Graphene Oxide hetero-structure thin films

Resistive switching behavior in Graphene oxide (GO) is well studied, however, the various mechanisms responsible for this phenomenon are still under extensive debate. We present repeatable bipolar resistive switching in GO thin films sandwiched between two insulating polymer PVDF (Polyvinylidene Fluoride) grown on conducting indium tin oxide (ITO) covered glass substrate. The device heterostructure (Al/PVDF/GO/PVDF/ITO) showed bipolar resistance states switching between low resistance state (LRS) to high resistance state (HRS) with a large ON/OFF ratio of 103 and resistance retention potential up to 104 s. In LRS, in the low applied voltage region, ohmic conduction was the main reason for current conduction in devices; however, traps filled/assisted conduction mechanism dominates in the higher voltage region. The PVDF/GO/PVDF heterostructure shows that oxygen vacancies are responsible for the formation of current conducting filaments. The low operating voltage (<3 V) and long-term stability of resistance states make it a promising candidate for possible applications as Resistive Random Access Memory (ReRAM) elements.

Development of Ni-Ferrite-Based PVDF Nanomultiferroics

Thin-film polyvinylidene fluoride (PVDF)–spinel ferrite nanocomposites with 0–3 connectivity and varying composition, i.e., (1 − x)PVDF–xNiFe2O4 (x = 0.05, 0.1, 0.15), have been fabricated by a solution-casting route. The basic crystal data and microstructure of the composite samples were obtained by x-ray powder diffraction analysis and scanning electron microscopy, respectively. Preliminary structural analysis showed the presence of polymeric electroactive β-phase of PVDF (matrix) and spinel ferrite (filler) phase in the composites. The composites were found to be flexible with high relative dielectric constant (er) and low loss tangent (tan δ). Detailed studies of their electrical characteristics using complex impedance spectroscopy showed the contributions of bulk (grains) and grain boundaries in the resistive and capacitive properties of the composites. Study of the frequency-dependent electrical conductivity at different temperatures showed that Jonscher’s power law could be used to interpret the transport properties of the composites. Important experimental data and results obtained from magnetic as well ferroelectric hysteresis loops and the first-order magnetoelectric coefficient suggest the suitability of some of these composites for fabrication of multifunctional devices. The low electrical conductivity, high dielectric constant, and low loss tangent suggest that such composites could be used in capacitor devices.

Crystal Structure Regulation of Ferroelectric Poly(vinylidene fluoride) via Controlled Melt–Recrystallization

Polyvinylidene fluoride (PVDF) is a known polymer with pronounced polymorphs. Among these polymorphs, the β and γ form crystals with strongest piezo- and pyro-electric activities of polymeric materials have attracted much attention. We report here a simple melt–recrystallization approach for producing γ-phase-rich PVDF thin films through selective melting and subsequent recrystallization. The proposed approach comprises the selective melting of both the nonpolar α-PVDF and polar γ-PVDF crystals but not the stable γ′-PVDF ones and subsequent isothermal recrystallization at 160 °C. During the recrystallization process, the nonmelting stable γ′-PVDF crystals can induce the direct γ-PVDF crystallization of the melt. In contrast, locally ordered domains survived in the molten α-PVDF crystal regions also result in a direct formation of γ-PVDF crystals. This is of great importance to fabricate high-quality thin films of γ-PVDF crystals for advanced applications.

Towards β-phase formation probability in spin coated PVDF thin films

This work aimed towards the study on variations in the percentage of beta-phase in Poly vinylidene fluoride (PVDF) thin films deposited by spin coating technique. PVDF is a semi-crystalline polymer which exhibits alpha, beta, gamma and delta polymorphs. Among these polymorphs, generally it crystallizes in a non-polar alpha-phase, which is of little importance as far as its applications are concerned. However, the beta-phase, which exhibits spontaneous polarity created tremendous interest and showed a path towards the devices based on its pyro-and piezoelectric properties. Fourier Transform Infrared (FTIR) spectroscopy and XRD techniques were used to study the percentage of formation of beta-phase in spin coated PVDF thin films at different processing conditions viz. spin rotation speed (rpm), solution concentration and annealing temperature. We identified the beta-phase percentage in PVDF thin films, which are (i) Deposited with different rotation speeds ranging from 1000 to 9000 rpm, (ii) Annealed at different temperatures viz.; room temperature to 100C, and (iii) Deposited at various solution concentrations. It is identified that percentage of formation of beta-phase is high in the films deposited with 15(w/v)% solution concentration which is annealed at 100C. The films deposited at higher rpm is showing low enhancement in the beta-phase with annealing temperature.

Structural and Optical Studies on Sol-gel Composites of Nickel-Doped Nanocrystalline Zinc Oxide/Polyvinylidene Fluoride

ABSTRACTNickel-doped nanocrystalline ZnO with three different Ni concentrations was incorporated in polyvinylidene fluoride thin film for obtaining free-standing flexible film by sol-gel technique. The effect of Ni–ZnO loading on the optical and microstructural properties of the Ni–ZnO/polyvinylidene fluoride composite films was studied. X-ray photoelectron spectroscopy and Raman studies were performed to characterize the bonding environment. Fluorine-terminated surface showed a strong F1 s peak located at ∼695 eV arising out of C–F bonds. Existence of β phase of polyvinylidene fluoride along with the presence of ZnO nanocrystals were indicated by Raman studies. Secondary ion mass spectrometry studies indicated the distribution of Ni–ZnO particles in the polyvinylidene fluoride matrix.

Real-Time Deflection Monitoring for Milling of a Thin-Walled Workpiece by Using PVDF Thin-Film Sensors with a Cantilevered Beam as a Case Study.

Thin-walled workpieces, such as aero-engine blisks and casings, are usually made of hard-to-cut materials. The wall thickness is very small and it is easy to deflect during milling process under dynamic cutting forces, leading to inaccurate workpiece dimensions and poor surface integrity. To understand the workpiece deflection behavior in a machining process, a new real-time nonintrusive method for deflection monitoring is presented, and a detailed analysis of workpiece deflection for different machining stages of the whole machining process is discussed. The thin-film polyvinylidene fluoride (PVDF) sensor is attached to the non-machining surface of the workpiece to copy the deflection excited by the dynamic cutting force. The relationship between the input deflection and the output voltage of the monitoring system is calibrated by testing. Monitored workpiece deflection results show that the workpiece experiences obvious vibration during the cutter entering the workpiece stage, and vibration during the machining process can be easily tracked by monitoring the deflection of the workpiece. During the cutter exiting the workpiece stage, the workpiece experiences forced vibration firstly, and free vibration exists until the amplitude reduces to zero after the cutter exits the workpiece. Machining results confirmed the suitability of the deflection monitoring system for machining thin-walled workpieces with the application of PVDF sensors.

PVDF sensor based monitoring of single-point cutting

A low-cost, high fidelity measurement system consisting of a thin film polyvinylidene fluoride (PVDF) piezoelectric strain rosette and data logging electronics has been designed, fabricated and evaluated for monitoring the dynamic cutting forces and torque in single-point cutting processes, specifically turning and boring. Physics-based models are used to relate the measured voltage to the process forces and the torque. Using assumptions about particular strain components, simplified strain sensor rosettes are developed to isolate particular strains of interest. Wired and wireless communication methods are demonstrated to transmit the dynamic strains measured by the sensors to a data logging base station. The proposed methods are experimentally validated through comparison with quartz-based piezoelectric cutting force dynamometer measurements.