Tuning Dielectric Properties with Nanofiller Dimensionality in Polymer Nanocomposites

Polymer nanocomposites hold great potential as dielectrics for energy storage devices and flexible electronics. The structural architecture of the nanofillers is expected to play a crucial role in the fundamental mechanisms governing the electrical breakdown and dielectric properties of the nanocomposites. However, the effect of nanofiller structure and dimensionality on these properties has not been studied thoroughly to date. This study explores the critical relationship between nanofiller dimensionality and dielectric properties in polymer nanocomposites. We fabricated polyvinylidene fluoride (PVDF) nanocomposites by incorporating a range of carbon-based nanofillers separately, including zero-dimensional (0D) carbon black (CB), one-dimensional (1D) multiwalled carbon nanotubes (MWCNT), 1D single-walled carbon nanotubes (SWCNT), two-dimensional (2D) reduced graphene oxide (rGO), and three-dimensional (3D) graphite. The frequency-dependent (1 kHz to 1 MHz) dielectric permittivity (k) of the nanocomposites at the same concentration of nanofillers demonstrated a hierarchical order, with MWCNT showing the highest permittivity (∼400%), succeeded by rGO (∼360%), CB (∼290%), SWCNT (∼230%), and graphite (∼70%), respectively. The temperature-dependent (50-150 °C) dielectric spectroscopy revealed high k with increasing temperature due to the enhanced dipole movement. However, their dielectric breakdown strength and energy densities were not correlated to k and exhibited the following order: SWCNT > MWCNT > CB > rGO > graphite. As the electrical breakdown depends upon the nanocomposites' mechanical strength, we correlated the mechanical properties with the nanofiller dimensionality, and Young's modulus followed the 1D ≈ 2D > 0D > 3D order. These findings will provide fundamental insights into designing tunable, conducive nanofiller-based nanocomposites in next-generation flexible electronics and capacitive energy storage devices.

A novel flexible CO2 gas sensor based on polyvinyl alcohol/yttrium oxide nanocomposite films

Polyvinyl alcohol/yttrium oxide (PVA/Y2O3) nanocomposite films with five different weight ratios of PVA and Y2O3 nanoparticles (NPs) were prepared using a simple solution casting method. The prepared polymer nanocomposite (PNC) films were examined using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). FTIR spectra exhibited a strong interaction between the PVA matrix and Y2O3 NPs. SEM results indicated that Y2O3 NPs were properly dispersed in the PVA matrix. The thermal stability of the PVA/Y2O3 nanocomposite films was found to be dependent on Y2O3 NP loading (wt%) in the nanocomposite films. Furthermore, chemiresistive gas sensing properties of the PVA/Y2O3 nanocomposite films were evaluated and the sensing parameters including sensing response, operating temperature, selectivity, stability, response/recovery time, and repeatability were systematically investigated based on the change in electrical resistance of the nanocomposite film in the presence of carbon dioxide (CO2) gas. The maximum sensing response (S) of 92.72% at a concentration of 100 ppm under an optimized operating temperature of 100 °C with a fast response/recovery time of ∼15/11 s towards CO2 gas detection was observed for the PVA/Y2O3 nanocomposite film with 5 wt% loading of Y2O3 NPs in the PVA matrix. The finding in this work suggest that Y2O3 NPs are sufficiently fast as a CO2 gas sensing material at a relatively low operating temperature. Moreover, the key role of the Y2O3 NPs in modulating the electrical and gas sensing properties of the PVA matrix is discussed here.

Improved Energy Harvesting Ability of Single-Layer Binary Fiber Nanocomposite Membrane for Multifunctional Wearable Hybrid Piezoelectric and Triboelectric Nanogenerator and Self-Powered Sensors

While wearable self-powered electronic devices have shown promising improvements, substantial challenges persist in enhancing their electrical output and structural performance. In this work, a working mechanism involving simultaneous piezoelectric and triboelectric conversion within a monolayer-structured membrane is proposed. Single-layer binary fiber nanocomposite membranes (SBFNMs) (PVDF/CNTX@PAN/CNTX, DPCPCX) with two distinct interpenetrating nanocomposite fibers were created through co-electrospinning, incorporating multiwalled carbon nanotubes (CNTs) into polyvinylidene fluoride (PVDF) and polyacrylonitrile (PAN), respectively. The resulting membrane demonstrated an exceptional synergistic effect of piezoelectricity and triboelectricity along with a high machine-to-electric conversion capability. The addition of CNTs increased the PVDF β-phase and the PAN planar zigzag conformation. As a result, the DPCPC0.5-SBFNMs-based piezoelectric nanogenerator exhibited excellent electrical output (187 V, 8.0 μA, and 1.52 W m-2), maintaining an exceptionally high level of output voltage compared with other piezoelectric nanogenerators. It successfully illuminated 50 commercial light-emitting diodes simultaneously. The output voltage of DPCPC0.5-SBFNMs was 5.1 and 4.6 times higher than that of PAN or PVDF single-fiber membranes, respectively. Furthermore, the peak voltage of DPCPC0.5-SBFNMs exceeded that of co-electrospinning PVDF/CNT1.0@PAN (DPCP1.0) and PVDF@PAN/CNT1.0 (DPPC1.0) by 20 and 10 V, respectively. The piezoelectric sensor made of DPCPC0.5-SBFNMs accurately sensed human movement, ranging from tiny to large, and demonstrated utility as an alarm in medical treatment, fire fighting, and monitoring. Endogenous triboelectricity is proposed in SBFNM piezoelectric materials, enhancing electromechanical conversion and electrical output capacity, thereby promising a wide application potential in self-powered wearable electronic devices.

Electrospun nanofibers: promising nanomaterials for biomedical applications

With the rapid development of nanotechnology and nanomaterials science, electrospun nanofibers emerged as a new material with great potential for a variety of applications. Electrospinning is a simple and adaptable process for generation of nanofibers from a viscoelastic fluid using electrostatic repulsion between surface charges. Electrospinning has been used to manufacture nanofibers with low diameters from a wide range of materials. Electrospinning may also be used to construct nanofibers with a variety of secondary structures, including those having a porous, hollow, or core–sheath structure. Due to many attributes including their large specific surface area and high porosity, electrospun nanofibers are suitable for biosensing and environmental monitoring. This book chapter discusses the different methods of nanofiber preparations and the challenges involved, recent research progress in electrospun nanofibers, and the ways to commercialize these nanofiber materials.

Electrospun Poly (Vinylidene Fluoride-Co-Hexafluoropropylene) Nanofiber Membranes for Brine Treatment via Membrane Distillation

The major challenge for membrane distillation (MD) is the membrane wetting resistance induced by pollutants in the feed solution. The proposed solution for this issue was to fabricate membranes with hydrophobic properties. Hydrophobic electrospun poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofiber membranes were produced for brine treatment using the direct-contact membrane distillation (DCMD) technique. These nanofiber membranes were prepared from three different polymeric solution compositions to study the effect of solvent composition on the electrospinning process. Furthermore, the effect of the polymer concentration was investigated by preparing polymeric solutions with three different polymer percentages: 6, 8, and 10%. All of the nanofiber membranes obtained from electrospinning were post-treated at varying temperatures. The effects of thickness, porosity, pore size, and liquid entry pressure (LEP) were studied. The hydrophobicity was determined using contact angle measurements, which were investigated using optical contact angle goniometry. The crystallinity and thermal properties were studied using DSC and XRD, while the functional groups were studied using FTIR. The morphological study was performed with AMF and described the roughness of nanofiber membranes. Finally, all of the nanofiber membranes had enough of a hydrophobic nature to be used in DCMD. A PVDF membrane filter disc and all nanofiber membranes were applied in DCMD to treat brine water. The resulting water flux and permeate water quality were compared, and it was discovered that all of the produced nanofiber membranes showed good behavior with varying water flux, but the salt rejection was greater than 90%. A membrane prepared from DMF/acetone 5-5 with 10% PVDF-HFP provided the perfect performance, with an average water flux of 44 kg.m^-2.h^-1 and salt rejection of 99.8%.

Conjugated Polymer-Based Nanocomposites for Pressure Sensors

Flexible sensors are the essential foundations of pressure sensing, microcomputer sensing systems, and wearable devices. The flexible tactile sensor can sense stimuli by converting external forces into electrical signals. The electrical signals are transmitted to a computer processing system for analysis, realizing real-time health monitoring and human motion detection. According to the working mechanism, tactile sensors are mainly divided into four types-piezoresistive, capacitive, piezoelectric, and triboelectric tactile sensors. Conventional silicon-based tactile sensors are often inadequate for flexible electronics due to their limited mechanical flexibility. In comparison, polymeric nanocomposites are flexible and stretchable, which makes them excellent candidates for flexible and wearable tactile sensors. Among the promising polymers, conjugated polymers (CPs), due to their unique chemical structures and electronic properties that contribute to their high electrical and mechanical conductivity, show great potential for flexible sensors and wearable devices. In this paper, we first introduce the parameters of pressure sensors. Then, we describe the operating principles of resistive, capacitive, piezoelectric, and triboelectric sensors, and review the pressure sensors based on conjugated polymer nanocomposites that were reported in recent years. After that, we introduce the performance characteristics of flexible sensors, regarding their applications in healthcare, human motion monitoring, electronic skin, wearable devices, and artificial intelligence. In addition, we summarize and compare the performances of conjugated polymer nanocomposite-based pressure sensors that were reported in recent years. Finally, we summarize the challenges and future directions of conjugated polymer nanocomposite-based sensors.

MEMS-Based Tactile Sensors: Materials, Processes and Applications in Robotics

Commonly encountered problems in the manipulation of objects with robotic hands are the contact force control and the setting of approaching motion. Microelectromechanical systems (MEMS) sensors on robots offer several solutions to these problems along with new capabilities. In this review, we analyze tactile, force and/or pressure sensors produced by MEMS technologies including off-the-shelf products such as MEMS barometric sensors. Alone or in conjunction with other sensors, MEMS platforms are considered very promising for robots to detect the contact forces, slippage and the distance to the objects for effective dexterous manipulation. We briefly reviewed several sensing mechanisms and principles, such as capacitive, resistive, piezoresistive and triboelectric, combined with new flexible materials technologies including polymers processing and MEMS-embedded textiles for flexible and snake robots. We demonstrated that without taking up extra space and at the same time remaining lightweight, several MEMS sensors can be integrated into robotic hands to simulate human fingers, gripping, hardness and stiffness sensations. MEMS have high potential of enabling new generation microactuators, microsensors, micro miniature motion-systems (e.g., microrobots) that will be indispensable for health, security, safety and environmental protection.

N. P, Hassim MT, Song JI. Development of Self-Healing Carbon/Epoxy Composites with Optimized PAN/PVDF Core-Shell Nanofibers as Healing Carriers

Two-component self-healing carbon/epoxy composites were fabricated by incorporating healing agents between to carbon fiber laminates via the vacuum bagging method. Vinyl ester (VE), cobalt naphthalene (CN), and methyl ethyl ketone peroxide (MEKP) were encapsulated in a polyacrylonitrile (PAN)/Poly(vinylidene fluoride) (PVDF) shell via co-axial electrospinning. Varying nanofiber compositions were fabricated, namely, 10, 20, 30, and 40% PAN in PVDF nanofibers. The 20% PAN fibers were finalized as the shell material owing to their superior tensile properties and surface morphology. The behavior of the PAN/PVDF nanofibers encapsulating the healing agents was studied via Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA) to affirm the presence of the healing agents. Mechanical analysis in the presence of core-shell nanofibers indicated an enhancement of 7 and 5% in flexural strength and Izod impact strength, respectively. Three-point bending tests confirmed the autonomous healing characteristics of these nanofibers, which retained 62% of their initial strength after 24 h. FESEM and energy dispersive X-ray (EDX) analyses of the fracture surface confirmed that the resin was released from the nanofibers, restoring the initial properties of the composites.

Recent Progress in Conducting Polymer Composite/Nanofiber-Based Strain and Pressure Sensors

The Conducting of polymers belongs to the class of polymers exhibiting excellence in electrical performances because of their intrinsic delocalized π- electrons and their tunability ranges from semi-conductive to metallic conductive regime. Conducting polymers and their composites serve greater functionality in the application of strain and pressure sensors, especially in yielding a better figure of merits, such as improved sensitivity, sensing range, durability, and mechanical robustness. The electrospinning process allows the formation of micro to nano-dimensional fibers with solution-processing attributes and offers an exciting aspect ratio by forming ultra-long fibrous structures. This review comprehensively covers the fundamentals of conducting polymers, sensor fabrication, working modes, and recent trends in achieving the sensitivity, wide-sensing range, reduced hysteresis, and durability of thin film, porous, and nanofibrous sensors. Furthermore, nanofiber and textile-based sensory device importance and its growth towards futuristic wearable electronics in a technological era was systematically reviewed to overcome the existing challenges.

Structure Tuning and Electrical Properties of Mixed PVDF and Nylon Nanofibers

The paper specifies the electrostatic spinning process of specific polymeric materials, such as polyvinylidene fluoride (PVDF), polyamide-6 (PA6, Nylon-6) and their combination PVDF/PA6. By combining nanofibers from two different materials during the spinning process, new structures with different mechanical, chemical, and physical properties can be created. The materials and their combinations were subjected to several measurements: scanning electron microscopy (SEM) to capture topography; contact angle of the liquid wettability on the sample surface to observe hydrophobicity and hydrophilicity; crystallization events were determined by differential scanning calorimetry (DSC); X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FT-IR) to describe properties and their changes at the chemical level. Furthermore, for the electrical properties of the sample, the dielectric characteristics and the piezoelectric coefficient were measured. The advantage of the addition of co-polymers was to control the properties of PVDF samples and understand the reasons for the changed functionality. The innovation point of this work is the complex analysis of PVDF modification caused by mixing with nylon PA6. Here we emphasize that the application of nylon during the spin influences the properties and structure (polarization, crystallization) of PVDF.

PVDF Fibers Modification by Nitrate Salts Doping

The method of inclusion of various additives into a polymer depends highly on the material in question and the desired effect. In the case of this paper, nitride salts were introduced into polyvinylidene fluoride fibers prepared by electrospinning. The resulting changes in the structural, chemical and electrical properties of the samples were observed and compared using SEM-EDX, DSC, XPS, FTIR, Raman spectroscopy and electrical measurements. The observed results displayed a grouping of parameters by electronegativity and possibly the molecular mass of the additive salts. We virtually demonstrated elimination of the presence of the γ-phase by addition of Mg(NO₃)₂, Ca(NO₃)₂, and Zn(NO₃)₂ salts. The trend of electrical properties to follow the electronegativity of the nitrate salt cation is demonstrated. The performed measurements of nitrate salt inclusions into PVDF offer a new insight into effects of previously unstudied structures of PVDF composites, opening new potential possibilities of crystalline phase control of the composite and use in further research and component design.

Preparation, Physical Properties, and Applications of Water-Based Functional Polymer Inks

In this study, water-based functional polymer inks are prepared using different solvent displacement methods, in particular, polymer functional inks based on semiconducting polymer poly(3-hexylthiophene) and the ferroelectric polymer poly(vinylidene fluoride) and its copolymers with trifluoroethylene. The nanoparticles that are included in the inks are prepared by miniemulsion, as well as flash and dialysis nanoprecipitation techniques and we discuss the properties of the inks obtained by each technique. Finally, an example of the functionality of a semiconducting/ferroelectric polymer coating prepared from water-based inks is presented.

Flexible Nanogenerator from Electrospun PVDF-Polycarbazole Nanofiber Membranes for Human Motion Energy-Harvesting Device Applications

Poly(vinylidene difluoride) (PVDF) has become the polymer matrix of choice for fabrication of wearable electronics and physiological monitoring devices. Despite possessing a high piezoelectric constant, additives are required to increase the charge transfer from PVDF matrix to connected signal readout units. Many of these additives also stabilize the β-phase of PVDF, which is associated with highest piezoelectric coefficients. However, most of the additives used are often brittle ceramic-phase materials resulting in decreased flexibility of the devices and offsetting the gain in β-phase content. Intrinsically conducting polymers (ICP), on the other hand, are ideal candidates to improve the device-related properties of PVDF, due to their higher flexibility than ceramic fillers as well as ability to form conducting network in PVDF membranes. This work reports the performance and device feasibility of PVDF-polycarbazole (PCZ) electrospun nanofiber membranes. A higher β-phase was observed by FTIR spectroscopy in PVDF/PCZ compared to other PVDF phases. Moreover, a higher open-circuit potential was recorded over PVDF/polyaniline composites, which were studied for comparison. The addition of PCZ reduced the flexibility of pure PVDF nanofibers by 20% only. Besides, the work investigated the bacterial biofouling and cell compatibility of the matrix, as essential properties to examine any putative medical device application. PVDF/PCZ membranes were then used to develop a nanogenerator, which was capable of instantly lighting an entire LED array employing the rectified output power, and charged up a 2.2 μF capacitors using a bridge rectifier through a vertical compressive force applied periodically. Finally, the nanogenerator demonstrated electrical energy harvesting from movements of various parts of the human body, such as toe and heel movement and wrist bending. In conclusion, PCZ can be considered as an attractive, biocompatible, and anti-biofouling conducting polymer for electrical actuation and flexible electronic device applications.

In situ-grown organo-lead bromide perovskite-induced electroactive γ-phase in aerogel PVDF films: an efficient photoactive material for piezoelectric energy harvesting and photodetector applications

The unique combination of piezoelectric energy harvesters and light detectors progressively strengthens their application in the development of modern electronics. Here, for the first time, we fabricated a polyvinylidene fluoride (PVDF) and formamidinium lead bromide nanoparticle (FAPbBr3 NP)-based composite aerogel film (FAPbBr3/PVDF) for harvesting electrical energy and photodetector applications. The uniform distribution of FAPbBr3 NPs in FAPbBr3/PVDF was achieved via the in situ synthesis of FAPbBr3 NPs in the PVDF matrix, which led to the stabilization of the γ-phase. The freeze-drying process induced an interconnected porous architecture in the composite film, making it more sensitive to small mechanical stimuli. Owing to this unique fabrication technique, the constructed aerogel film-based nanogenerator (FPNG) exhibited an output voltage and current of ∼26.2 V and ∼2.1 μA, respectively, which were 5-fold higher than that of the nanogenerator with the pure PVDF film. Also, the sensitivity of FPNG upon the irradiation of light was demonstrated by the output voltage reduction of ∼38%, indicating its capability as a light sensing device. Furthermore, the prepared FAPbBr3/PVDF composite was found to be an efficient candidate for light detection applications. A simple planar photodetector was fabricated with the 8.0 wt% FAPbBr3 NP-loaded PVDF composite, which displayed very high responsivity (8 A/W) and response speed of 2.6 s. Thus, this exclusive combination of synthesis and fabrication for the preparation of electro-active films opens a new horizon in the piezoelectric community for effective energy harvesting and light detector applications.

Conductive Electrospun Nanofiber Mats

Conductive nanofiber mats can be used in a broad variety of applications, such as electromagnetic shielding, sensors, multifunctional textile surfaces, organic photovoltaics, or biomedicine. While nanofibers or nanofiber from pure or blended polymers can in many cases unambiguously be prepared by electrospinning, creating conductive nanofibers is often more challenging. Integration of conductive nano-fillers often needs a calcination step to evaporate the non-conductive polymer matrix which is necessary for the electrospinning process, while conductive polymers have often relatively low molecular weights and are hard to dissolve in common solvents, both factors impeding spinning them solely and making a spinning agent necessary. On the other hand, conductive coatings may disturb the desired porous structure and possibly cause problems with biocompatibility or other necessary properties of the original nanofiber mats. Here we give an overview of the most recent developments in the growing field of conductive electrospun nanofiber mats, based on electrospinning blends of spinning agents with conductive polymers or nanoparticles, alternatively applying conductive coatings, and the possible applications of such conductive electrospun nanofiber mats.

PVDF Nanofiber Sensor for Vibration Measurement in a String

Flexible, self-powered and miniaturized sensors are extensively used in the areas of sports, soft robotics, health care and communication devices. Measurement of vibration is important for determining the mechanical properties of a structure, specifically the string tension in strings. In this work, a flexible, lightweight and self-powered sensor is developed and attached to a string to measure vibrations characteristics in strings. Electrospun poly(vinylidene) fluoride (PVDF) nanofibers are deposited on a flexible liquid crystal polymer (LCP) substrate for the development of the sensor. The electrospinning process is optimized for different needle sizes (0.34–0.84 mm) and flow rates (0.6–3 mL/h). The characterization of the sensor is done in a cantilever configuration and the test results indicate the sensor’s capability to measure the frequency and strain in the required range. The comparison of the results from the developed PVDF sensor and a commercial Laser Displacement Sensor (LDS) showed good resemblance (±0.2%) and a linear voltage profile (0.2 mV/με). The sensor, upon attachment to a racket string, is able to measure single impacts and sinusoidal vibrations. The repeatability of the results on the measurement of vibrations produced by an impact hammer and a mini shaker demonstrate an exciting new application for piezoelectric sensors.

Piezoelectric Response of Aligned Electrospun Polyvinylidene Fluoride/Carbon Nanotube Nanofibrous Membranes

Polyvinylidene fluoride (PVDF) shows piezoelectricity related to its β-phase content and mechanical and electrical properties influenced by its morphology and crystallinity. Electrospinning (ES) can produce ultrafine and well-aligned PVDF nanofibers. In this study, the effects of the presence of carbon nanotubes (CNT) and optimized ES parameters on the crystal structures and piezoelectric properties of aligned PVDF/CNT nanofibrous membranes were examined. The optimal β content and piezoelectric coefficient (d₃₃) of the aligned electrospun PVDF reached 88% and 27.4 pC/N; CNT addition increased the β-phase content to 89% and d₃₃ to 31.3 pC/N. The output voltages of piezoelectric units with aligned electrospun PVDF/CNT membranes increased linearly with applied loading and showed good stability during cyclic dynamic compression and tension. The sensitivities of the piezoelectric units with the membranes under dynamic compression and tension were 2.26 mV/N and 4.29 mV/%, respectively. In bending tests, the output voltage increased nonlinearly with bending angle because complicated forces were involved. The output of the aligned membrane-based piezoelectric unit with CNT was 1.89 V at the bending angle of 100°. The high electric outputs indicate that the aligned electrospun PVDF/CNT membranes are potentially effective for flexible wearable sensor application with high sensitivity.

Self-Assembled Nanorod Structures on Nanofibers for Textile Electrochemical Capacitor Electrodes with Intrinsic Tactile Sensing Capabilities

A novel polyaniline nanorod (PAniNR) three-dimensional structure was successfully grown on flexible polyacrylonitrile (PAN) nanofiber substrate as the electrode material for electrochemical capacitors (ECs), constructed via self-stabilized dispersion polymerization process. The electrode offered desired mechanical properties such as flexibility and bendability, whereas it maintained optimal electrochemical characteristics. The electrode and the assembled EC cell also achieved intrinsic piezoresistive sensing properties, leading to real-time monitoring of excess mechanical pressure and bending during cell operations. The PAniNR@PAN electrodes show an average diameter of 173.6 nm, with the PAniNR growth of 50.7 nm in length. Compared to the electrodes made from pristine PAni, the gravimetric capacitance increased by 39.8% to 629.6 F/g with aqueous acidic electrolyte. The electrode and the assembled EC cell with gel electrolyte were responsive to tensile, compressive, and bending stresses with a sensitivity of 0.95 MPa^-1.

Electroactive polymers for tissue regeneration: Developments and perspectives

Human body motion can generate a biological electric field and a current, creating a voltage gradient of -10 to -90 mV across cell membranes. In turn, this gradient triggers cells to transmit signals that alter cell proliferation and differentiation. Several cell types, counting osteoblasts, neurons and cardiomyocytes, are relatively sensitive to electrical signal stimulation. Employment of electrical signals in modulating cell proliferation and differentiation inspires us to use the electroactive polymers to achieve electrical stimulation for repairing impaired tissues. Electroactive polymers have found numerous applications in biomedicine due to their capability in effectively delivering electrical signals to the seeded cells, such as biosensing, tissue regeneration, drug delivery, and biomedical implants. Here we will summarize the electrical characteristics of electroactive polymers, which enables them to electrically influence cellular function and behavior, including conducting polymers, piezoelectric polymers, and polyelectrolyte gels. We will also discuss the biological response to these electroactive polymers under electrical stimulation. In particular, we focus this review on their applications in regenerating different tissues, including bone, nerve, heart muscle, cartilage and skin. Additionally, we discuss the challenges in tissue regeneration applications of electroactive polymers. We conclude that electroactive polymers have a great potential as regenerative biomaterials, due to their ability to stimulate desirable outcomes in various electrically responsive cells.

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.

Poly(vinylidene fluoride)/poly(3-methylthiophene) core–shell nanocomposites with improved structural and electronic properties of the conducting polymer component

Significant improvements in structural, electronic and sensory properties of P3MT have been achieved due to its synthesis in the presence of submicron PVDF particles.

Poly(vinylidene fluoride)/NH2-Treated Graphene Nanodot/Reduced Graphene Oxide Nanocomposites with Enhanced Dielectric Performance for Ultrahigh Energy Density Capacitor

This work describes a ternary nanocomposite system, composed of poly(vinylidene fluoride) (PVDF), NH2-treated graphene nanodots (GNDs), and reduced graphene oxides (RGOs), for use in high energy density capacitor. When the RGO sheets were added to PVDF matrix, the β-phase content of PVDF became higher than that of the pristine PVDF. The surface-treatment of GNDs with an ethylenediamine can promote the hydrogen bonding interactions between the GNDs and PVDF, which promote the formation of β-phase PVDF. This finding could be extended to combine the advantages of both RGO and NH2-treated GND for developing an effective and reliable means of preparing PVDF/NH2-treated GND/RGO nanocomposite. Relatively small amounts of NH2-treated GND/RGO cofillers (10 vol %) could make a great impact on the α → β phase transformation, dielectric, and ferroelectric properties of the ternary nanocomposite. The resulting PVDF/NH2-treated GND/RGO nanocomposite exhibited higher dielectric constant (ε' ≈ 60.6) and larger energy density (U(e) ≈ 14.1 J cm(-3)) compared with the pristine PVDF (ε' ≈ 11.6 and U(e) ≈ 1.8 J cm(-3)).

Development of magnetoelectric CoFe2O4 /poly(vinylidene fluoride) microspheres

Magnetoelectric microspheres based on piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive CoFe₂O₄ (CFO), a novel morphology for polymer-based ME materials, have been developed by an electrospray process.

Effect of electrospinning parameters and polymer concentrations on mechanical-to-electrical energy conversion of randomly-oriented electrospun poly(vinylidene fluoride) nanofiber mats

Electrospun PVDF nanofibers with uniform fiber-morphology, smaller diameter and higher β crystal phase content show higher mechanical-to-electric energy conversion ability.

Thermally responsive behaviour of the electrical resistance of electrospun P(NIPAm-co-NMA)/Ag composite nanofibers

The electrical resistance of electrospun P(NIPAm-co-NMA)/Ag fibers exhibits a high sensitivity to the change of temperature around the LCST of the polymer, making them promising candidates for flexible sensors.

Synthesis of few-layered MoS₂ nanosheet-coated electrospun SnO₂ nanotube heterostructures for enhanced hydrogen evolution reaction

In this work, we report the fabrication of low crystalline, few-layered MoS₂ nanosheet-coated electrospun SnO₂ nanotube (MoS₂/SnO₂) heterostructures with three-dimensional configurations by electrospinning combined with a one-step solvothermal approach. The morphologies and compositions of the as-prepared hybrid nanotubes were characterized by field-emission scanning electron microscopy, transmission electron microscopy, ICP-AES, BET method, X-ray diffraction and X-ray photoelectron spectroscopy. Results show that SnO₂ nanotubes are uniformly covered by sheet-like MoS₂ subunits on both outer and inner surfaces. The electrocatalytic activity of MoS₂/SnO₂ heterostructures towards a hydrogen evolution reaction was examined using linear sweep voltammetry and AC impedance measurements. It is shown that the MoS₂/SnO₂ modified electrode exhibits excellent catalytic activity for hydrogen evolution with low overpotential, a small Tafel slope and high current density.