Stretchable Electrospun PVDF-HFP/Co-ZnO Nanofibers as Piezoelectric Nanogenerators

Tunable Mechanical and Electrical Properties of Coaxial Electrospun Composite Nanofibers of P(VDF-TrFE) and P(VDF-TrFE-CTFE)

The coaxial core/shell composite electrospun nanofibers consisting of relaxor ferroelectric P(VDF-TrFE-CTFE) and ferroelectric P(VDF-TrFE) polymers are successfully tailored towards superior structural, mechanical, and electrical properties over the individual polymers. The core/shell-TrFE/CTFE membrane discloses a more prominent mechanical anisotropy between the revolving direction (RD) and cross direction (CD) associated with a higher tensile modulus of 26.9 MPa and good strength-ductility balance, beneficial from a better degree of nanofiber alignment, the increased density, and C-F bonding. The interfacial coupling between the terpolymer P(VDF-TrFE-CTFE) and copolymer P(VDF-TrFE) is responsible for comparable full-frequency dielectric responses between the core/shell-TrFE/CTFE and pristine terpolymer. Moreover, an impressive piezoelectric coefficient up to 50.5 pm/V is achieved in the core/shell-TrFE/CTFE composite structure. Our findings corroborate the promising approach of coaxial electrospinning in efficiently tuning mechanical and electrical performances of the electrospun core/shell composite nanofiber membranes-based electroactive polymers (EAPs) actuators as artificial muscle implants.

Multifunctional Oil Absorption with Macroporous Polystyrene Fibers Incorporating Silver-Doped ZnO

Hydrophobic microporous polystyrene (PS) fibers are fabricated by a solvent-induced phase-separation-assisted electrospinning method. Zinc oxide (ZnO) and silver-doped zinc oxide (Ag-ZnO) nanomaterials with variable morphologies are added to the PS fibers, to investigate the influence of multifunctional nanofiller addition on the porosity and consequent oil-adsorbing properties for different oil types. The doping of silver as well as the uniformity in particle distribution are confirmed by scanning electron microscopy and the energy-dispersive spectral analyses. The porosity of the fibers and their crystallinity effect depend on the hydrophobicity and surface properties of these microporous nanofilled fibers. Ag-ZnO, specifically in 2 wt %, enhanced the pore size and distribution in PS porous fibers, thereby enhancing the oil-adsorbing property and its hydrophobicity. In-depth analysis of the oil adsorption mechanism is done for the fibers, both qualitatively and quantitatively, to demonstrate its correlation with the structural integrity of the fibers. The PS/2Ag-ZnO composite also exhibits the highest antibacterial performance against Staphylococcus aureus, a general indication of antibiological fouling properties of these oil-separating films. The antifouling/antibacterial activity of the nanoparticles and high oil sorption capacity of the highly porous PS composites show great potential for use in water-treatment-related applications.

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.

Wearable Nanogenerators: Working Principle and Self-Powered Biosensors Applications

Wearable self-powered sensors represent a theme of interest in the literature due to the progress in the Internet of Things and implantable devices. The integration of different materials to harvest energy from body movement or the environment to power up sensors or act as an active component of the detection of analytes is a frontier to be explored. This review describes the most relevant studies of the integration of nanogenerators in wearables based on the interaction of piezoelectric and triboelectric devices into more efficient and low-cost harvesting systems to power up batteries or to use the generated power to identify multiple analytes in self-powered sensors and biosensors.

A facile, sensitive and rapid sensing platform based on CoZnO for detection of fipronil; an environmental toxin

A sensitive detection of extremely toxic phenylpyrazole insecticide, 'Fipronil' is presented. Currently, the advancement of approaches for the detection of insecticides at low concentrations with less time is important for environmental safety assurance. Considering this fact, an effort has been made to develop an electrospun CoZnO nanofiber (NF) based label-free electrochemical system for the detection of fipronil. The CoZnO NF were characterized using different techniques including field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-Ray Analysis (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman Spectroscopy. Based on the experimental results, the proposed platform displayed a linear response for fipronil in the attogram/mL range despite the multiple interfering agents. The sensitivity of the device was found to be 3.99 Kῼ (g/ml)^-1 cm^-2. Limit of detection (LOD) and limit of quantification (LOQ) were calculated and found to be 112 ag mL^-1 and 340 ag mL^-1 respectively. Further, this proposed sensor will be implemented in the fields for the rapid and proficient detection of the real samples.

Core-Shell Nanofibers of Polyvinylidene Fluoride-based Nanocomposites as Piezoelectric Nanogenerators

Flexible piezoelectric nanogenerators (PENG) are widely applied to harvest sustainable energy from multiple energy sources. The rational and simple design of PENG have great potential in soft electronics. Here we design a highly flexible PENG using the polyvinylidene fluoride (PVDF) and its copolymer, polyvinylidene hexafluoropropylene (PVDF-HFP) with two nanoarchitectures of semiconducting metal oxides, TiO₂ and ZnO. The nanotubes of TiO₂ and nanoflowers of ZnO are embedded in these different polymeric media by solvent mixing, and new fiber mats are generated by coaxial electrospinning technique. This process aligns the dipoles of polymers and nanomaterials, which is normally a pre-requisite for higher piezo potential. With excellent mechanical strength and flexibility, the tailored lightweight fiber mats are capable of producing good output voltage (a maximum of 14 V) during different mechanical vibrations at various frequencies and in response to human motions. The hybrid nanocomposite PENG is durable and inexpensive and has possible applications in wearable electronics.

Fabrication of piezoelectric poly(L-lactic acid)/BaTiO3 fibre by the melt-spinning process

Poly(l-lactic acid) (PLLA) based piezoelectric polymers are gradually becoming the substitute for the conventional piezoelectric ceramic and polymeric materials due to their low cost and biodegradable, non-toxic, piezoelectric and non-pyroelectric nature. To improve the piezoelectric properties of melt-spun poly(l-lactic acid) (PLLA)/BaTiO₃, we optimized the post-processing conditions to increase the proportion of the β crystalline phase. The α → β phase transition behaviour was determined by two-dimensional wide-angle x-ray diffraction and differential scanning calorimetry. The piezoelectric properties of PLLA/BaTiO₃ fibres were characterised in their yarn and textile form through a tapping method. From these results, we confirmed that the crystalline phase transition of PLLA/BaTiO₃ fibres was significantly enhanced under the optimised post-processing conditions at a draw ratio of 3 and temperature of 120 °C during the melt-spinning process. The results indicated that PLLA/BaTiO₃ fibres could be a one of the material for organic-based piezoelectric sensors for application in textile-based wearable piezoelectric devices.

Self-powered flexible photodetectors based on Ag nanoparticle-loaded g-C3N4 nanosheets and PVDF hybrids: role of plasmonic and piezoelectric effects

Here we demonstrate novel self-powered photodetection using silver (Ag) nanoparticle-loaded two-dimensional graphitic carbon nitride (g-C₃N₄) nanosheets triggered by poly-vinylidene fluoride (PVDF)-based flexible piezoelectric nanogenerators. A self-poled PVDF-based nanogenerator has been obtained upon exploiting pristine g-C₃N₄ nanosheets as a filler material within the PVDF matrix. The fabricated nanogenerator devices are found to be highly efficient in generating the maximum voltage of ∼2.3 V and maximum power ∼110 μWatt/cm², upon finger tapping. Further, the integration of an additional layer of plasmonic Ag nanoparticle-loaded g-C₃N₄ nanosheets, has led to a significant enhancement of photoresponse. The hybrid plasmonic nanogenerator (with a strain of ∼0.021%) has resulted in self-powered photodetection with a photo-to-dark current ratio of ∼60, as compared to the unstrained device (∼2.0). In contrast to the usual behaviour (positive photoresponse), the exposure of an ultraviolet light lowers the output current indicating a negative photoresponse reported for the first time in such a system. The origin of such negative photoresponse has been attributed to the screening of piezopotential of PVDF by photogenerated carriers of g-C₃N₄ nanosheets. On the other hand, visible light-induced positive photoresponse has originated from the increment in the current, indicating the useful role of Ag nanoparticles in plasmon-induced hot electron transfer process.

Progress in lead-free piezoelectric nanofiller materials and related composite nanogenerator devices

Current piezoelectric device systems need a significant reduction in size and weight so that electronic modules of increasing capacity and functionality can be incorporated into a great range of applications, particularly in energy device platforms. The key question for most applications is whether they can compete in the race of down-scaling and an easy integration with highly adaptable properties into various system technologies such as nano-electro-mechanical systems (NEMS). Piezoelectric NEMS have potential to offer access to a parameter space for sensing, actuating, and powering, which is inflential and intriguing. Fortunately, recent advances in modelling, synthesis, and characterization techniques are spurring unprecedented developments in a new field of piezoelectric nano-materials and devices. While the need for looking more closely at the piezoelectric nano-materials is driven by the relentless drive of miniaturization, there is an additional motivation: the piezoelectric materials, which are showing the largest electromechanical responses, are currently toxic lead (Pb)-based perovskite materials (such as the ubiquitous Pb(Zr,Ti)O3, PZT). This is important, as there is strong legislative and moral push to remove toxic lead compounds from commercial products. By far, the lack of viable alternatives has led to continuing exemptions to allow their temporary use in piezoelectric applications. However, the present exemption will expire soon, and the concurrent improvement of lead-free piezoelectric materials has led to the possibility that no new exemption will be granted. In this paper, the universal approaches and recent progresses in the field of lead-free piezoelectric nano-materials, initially focusing on hybrid composite materials as well as individual nanoparticles, and related energy harvesting devices are systematically elaborated. The paper begins with a short introduction to the properties of interest in various piezoelectric nanomaterials and a brief description of the current state-of-the-art for lead-free piezoelectric nanostructured materials. We then describe several key methodologies for the synthesis of nanostructure materials including nanoparticles, followed by the discussion on the critical current and emerging applications in detail.

Solution Blow Spinning of Polyvinylidene Fluoride Based Fibers for Energy Harvesting Applications: A Review

Polyvinylidene fluoride (PVDF)-based piezoelectric materials (PEMs) have found extensive applications in energy harvesting which are being extended consistently to diverse fields requiring strenuous service conditions. Hence, there is a pressing need to mass produce PVDF-based PEMs with the highest possible energy harvesting ability under a given set of conditions. To achieve high yield and efficiency, solution blow spinning (SBS) technique is attracting a lot of interest due to its operational simplicity and high throughput. SBS is arguably still in its infancy when the objective is to mass produce high efficiency PVDF-based PEMs. Therefore, a deeper understanding of the critical parameters regarding design and processing of SBS is essential. The key objective of this review is to critically analyze the key aspects of SBS to produce high efficiency PVDF-based PEMs. As piezoelectric properties of neat PVDF are not intrinsically much significant, various additives are commonly incorporated to enhance its piezoelectricity. Therefore, PVDF-based copolymers and nanocomposites are also included in this review. We discuss both theoretical and experimental results regarding SBS process parameters such as solvents, dissolution methods, feed rate, viscosity, air pressure and velocity, and nozzle design. Morphological features and mechanical properties of PVDF-based nanofibers were also discussed and important applications have been presented. For completeness, key findings from electrospinning were also included. At the end, some insights are given to better direct the efforts in the field of PVDF-based PEMs using SBS technique.

Fabrication and Piezoresistive/Piezoelectric Sensing Characteristics of Carbon Nanotube/PVA/Nano-ZnO Flexible Composite

Flexible sensors with a high sensitivity and wide-frequency response are essential for structural health monitoring (SHM) while they are attached. Here, carbon nanotube (CNT) films doped with various PVA fractions (CNT/PVA) and ZnO nanowires (nano-ZnO) on zinc sheets were first fabricated by functionalized self-assembly and hydrothermal synthesis processes. A CNT/PVA/nano-ZnO flexible composite (CNT/PVA/ZnO) sandwiched with a zinc wafer was then prepared by the spin-coating method. The piezoresistive and/or piezoelectric capabilities of the CNT/PVA/ZnO composite were comprehensively investigated under cyclic bending and impact loading after it was firmly adhered to a substrate (polypropylene sheet or mortar plate). The results show that the piezoresistive sensitivity and linear stability of the CNT/PVA films doped with 20%, 50%, and 100% PVA during bending are 5.47%/mm, 11.082%/mm, and 11.95%/mm and 2.3%, 3.42%, and 4.78%, respectively. The piezoelectric sensitivity, linear stability, and response accuracy of the CNT/PVA/ZnO composite under impulse loading are 4.87 mV/lbf, 3.42%, and 1.496 ms, respectively. These merits support the use of CNT/PVA/ZnO as a piezoresistive and/or piezoelectric compound sensor to monitor the static/dynamic loads on concrete structures while it is attached.

Flexible Piezoelectric Nanogenerators Using Metal-doped ZnO-PVDF Films

Piezoelectric nanomaterial-polymer composites represent a unique paradigm for making flexible energy harvesting and sensing devices with enhanced devices' performance. In this work, we studied various metal doped ZnO nanostructures, fabricated and characterized ZnO nanoparticle-PVDF composite thin film, and demonstrated both enhanced energy generation and motion sensing capabilities. Specifically, a series of flexible piezoelectric nanogenerators (PENGs) were designed based on these piezoelectric composite thin films. The voltage output from cobalt (Co), sodium (Na), silver (Ag), and lithium (Li) doped ZnO-PVDF composite as well as pure ZnO-PVDF samples were individually studied and compared. Under the same experimental conditions, the Li-ZnO based device produces the largest peak-to-peak voltage (3.43 Vpp) which is about 9 times of that of the pure ZnO based device, where Co-ZnO, Na-ZnO and Ag-ZnO are 1.2, 4.9 and 5.4 times, respectively. In addition, the effect of doping ratio of Li-ZnO is studied, and we found that 5% is the best doping ratio in terms of output voltage. Finally, we demonstrated that the energy harvested by the device from finger tapping at ~2 Hz can charge a capacitor with a large output power density of 0.45 W/cm3 and light up an ultraviolet (UV) light-emitting diode (LED). We also showed the device as a flexible wearable motion sensor, where different hand gestures were detected by the device with distinctive output voltage amplitudes and patterns.

Enhanced Piezoelectricity of Electrospun Polyvinylidene Fluoride Fibers for Energy Harvesting

Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm-2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.

PVDF-Based Composition-Gradient Multilayered Nanocomposites for Flexible High-Performance Piezoelectric Nanogenerators

Recently, flexible energy generators with good performance have trigged enormous interest because of their great potential application in developing full flexible self-powered electronics. Herein, we reported a flexible high-performance piezoelectric nanogenerator (PNG) based on composition-gradient multilayered poly(vinylidene fluoride) (PVDF) nanocomposites wherein a novel three-dimensional (3D) carbon-based nanoparticle was employed as the nanofiller. Making use of this novel 3D nanofiller and composition-gradient concept, one can efficiently promote the interfacial coupling effect and induce internal strain inside the PVDF matrix, contributing to dramatically improved piezoelectricity and consequently output performance for PNG. With the excellent output ability, the PNG also demonstrated to be capable of operating in both d₃₃ and d₃₁ modes and possesses high stability as well as durability, confirming its applicability as green power source for full flexible electronic systems.

Construction of Infrared-Light-Responsive Photoinduced Carriers Driver for Enhanced Photocatalytic Hydrogen Evolution

Infrared light, more than 50% of the solar light energy, is long-termly ignored in the photocatalysis field due to its low photon energy. Herein, infrared-light-responsive photoinduced carriers driver is first constructed taking advantage of pyroelectric effect for enhancing photocatalytic hydrogen evolution. In order to give full play to its role, the photocatalytic reaction is localized on the surface and interface of the composite based on a new semi-immersion type heat collected photocatalytic microfiber system. The system is consisted of distinctive pyroelectric substrate poly(vinylidene fluoride-co-hexafluropropylene (PVDF-HFP), typical photothermal material carbon nanotube (CNT), and representative photocatalyst CdS. The transient photocurrent, electrochemical impedance spectroscopy, time-resolved photoluminescence and pyroelectric potential characterizations indicate that the infrared-light-responsive carriers driver significantly promotes the photogenerated charge separation, accelerates carrier migration, and prolongs carrier lifetime. The photocatalytic hydrogen evolution efficiency is remarkably improved more than five times with the highest average apparent quantum yield of 16.9%. It may open up new horizons to photocatalytic technology for the more efficient use of infrared light.

Design of an Ultrasensitive Flexible Bend Sensor Using a Silver-Doped Oriented Poly(vinylidene fluoride) Nanofiber Web for Respiratory Monitoring

We propose a design strategy to fabricate a flexible bend sensor (BS) with ultrasensitivity toward airflow using all-poly(vinylidene fluoride) (PVDF) nanofiber web-based sensing elements and electrodes to monitor human respiration. The unique electrospinning (rotational speed of collector of 2000 rpm and tip-to-collector distance of 4 cm) with silver nanoparticle interfacing was introduced to prepare a Ag-doped oriented PVDF nanofiber web with high β-phase content as a sensing element (AgOriPVDF, β-phase crystallinity ∼44.5%). After that, a portion of the prepared AgOriPVDF was processed into a flexible and electrically conductive electrode through an electroless silver plating technique (SP-AgOriPVDF). Interestingly, the encapsulated AgOriPVDF BS with the SP-AgOriPVDF electrode exhibited superior piezoelectric bending response (open-circuit peak-to-peak output voltage, V_p-p ≈ 4.6 V) to injected airflow, which is more than 200 times higher than that of the unpackaged randomly aligned PVDF nanofiber web BS with a conductive tape electrode (V_p-p ≈ 0.02 V). In addition, the factors influencing the bend sensitivity of the BS such as the β-phase content, nanofiber orientation, flexibility of the electrode, and so forth were thoroughly analyzed and then discussed. We also demonstrated that the AgOriPVDF BS has sufficient capability to detect and identify various respiratory signals, presenting a great potential for wearable applications, for example, smart respiratory protective equipment.

Enhanced magnetoelectric coupling and dielectric constant in flexible ternary composite electrospun fibers of PVDF-HFP loaded with nanoclay and NiFe2O4 nanoparticles

Magnetoelectric flexible composite fiber mats with superior room temperature magnetoelectric properties.

Smart Non-Woven Fiber Mats with Light-Induced Sensing Capability

This article is focused on the facile procedure for 2D graphene oxide (GO) fabrication, utilizing reversible de-activation polymerization approach and therefore enhanced compatibility with surrounding polymer matrix. Such tunable improvement led to a controllable sensing response after irradiation with light. The neat GO as well as surface initiated atom transfer radical polymerization (SI-ATRP) grafted particles were investigated by atomic force microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. To confirm the successful surface reduction, X-ray photoelectron spectroscopy and Raman spectroscopy was utilized. The composites in form of non-woven fiber mats containing ungrafted GO and controllably grafted GO with compact layer of polymer dispersed in poly(vinylidene-co-hexafluoropropylene) were prepared by electrospinning technique and characterized by scanning electron microscopy. Mechanical performance was characterized using dynamic mechanical analysis. Thermal conductivity was employed to confirm that the conducting filler was well-dispersed in the polymer matrix. The presented controllable coating with polymer layer and its impact on the overall performance, especially photo-actuation and subsequent contraction of the material aiming on the sensing applications, was discussed.

Electrospun Poly(vinylidene fluoride-trifluoroethylene)-Based Polymer Nanocomposite Fibers for Piezoelectric Nanogenerators

The present work deals with the preparation, characterization, and application of self-poled nanofibers using piezoelectric polymer poly(vinylidene fluoride-trifluoroethylene), zinc oxide, and exfoliated graphene oxide by electrospinning process. The characterization of nanofiber is carried by different techniques such as field emission scanning electron microscopy, Fourier transform Infrared spectroscopy, X-ray diffraction techniques, and dynamic contact mode electrostatic force microscopy. The nanofiber based piezoelectric nanoenergy generator devices are fabricated for analyzing the energy generating efficiency. Piezoelectric hybrid nanofibers are exhibiting better energy generating efficiency and identified as potential material for energy harvesting applications.

Improved Piezoelectric Performance of Electrospun PVDF Nanofibers with Conductive Paint Coated Electrode

Fabrication of Nanogenerators (NGs) using Electrospun polyvinylidene fluoride (PVDF) nanofibers for sensing and energy harvesting applications is a trending research due to its flexibility, biocompatibility, low-cost, etc. Different electrode materials, polymer composites had been proposed to increase the energy output. However, the contact area between the electrode material and nanofiber mat which helps to conduct more piezoelectric charges to the electrode surface are still unexplored especially at nanoscale level. In this paper, authors have proposed the use of low-cost carbon conductive paint to increase the contact area between the electrode and nanofiber mat. The electrode material is coated with conductive paint and the NG was fabricated with that electrode to compare the performances with conventional NG. Piezoelectric performance of the proposed NG has increased substantially as it generates an open circuit voltage [Formula: see text]) of 4.5[Formula: see text]V and short circuit current [Formula: see text]) of 25[Formula: see text]nA, whereas the conventional NG can only produce 1.6 [Formula: see text]) and 1.5[Formula: see text]nA [Formula: see text]). A drop test experiment was conducted, and the device consistency was verified experimentally.

Flexible Ferroelectret Polymer for Self-Powering Devices and Energy Storage Systems

Applying flexible materials for energy scavenging from ambient mechanical vibrations is a clean energy solution that can help alleviate electrical power demands in portable devices and wearable electronics. This work presents fundamental studies on a flexible ferroelectret polymer with a strong piezoelectric effect and its interface with self-powered and energy storage systems. A single-layered device with a thickness of 80 μm was used for characterizing the device's output voltage, current, transferred charge, and energy conversion efficiency. The potential capability of harvesting mechanical energy and delivering to system load is demonstrated by integrating the device into a fully integrated power management system. The theory for determining the harvested energy that is ultimately delivered to external electronic loads (or stored in a battery) is discussed. The maximum power delivery is found to be for a 600 MΩ load, which results in a device power density of 14.0 W/m³ for input mechanical forces with a frequency around 2 Hz.

Toward High Power Generating Piezoelectric Nanofibers: Influence of Particle Size and Surface Electrostatic Interaction of Ce-Fe2O3 and Ce-Co3O4 on PVDF

Development of flexible piezoelectric nanogenerator (PENG) is a real challenge for the next-generation energy-harvesting applications. In this paper, we report highly flexible PENGs based on poly(vinylidene fluoride) (PVDF)/2 wt % Ce-Fe₂O₃ and PVDF/2 wt % Ce-Co₃O₄ nanocomposite fibers. The incorporation of magnetic Ce-Fe₂O₃ and Ce-Co₃O₄ greatly affects the structural properties of PVDF nanofibers, especially the polymeric β and γ phases. In addition, the new composites enhanced the interfacial compatibility through electrostatic filler-polymer interactions. Both PVDF/Ce-Fe₂O₃ and PVDF/Ce-Co₃O₄ nanofibers-based PENGs, respectively, produce peak-to-peak output voltages of 20 and 15 V, respectively, with the corresponding output currents of 0.010 and 0.005 μA/cm² under the force of 2.5 N. Enhanced output performance of the flexible nanogenerator is correlated with the electroactive polar phases generated within the PVDF, in the presence of the nanomaterials. The designed nanogenerators respond to human wrist movements with the highest output voltage of 0.15 V, for the PVDF/Ce-Fe₂O₃ when subjected to hand movements. The overall piezoelectric power generation is correlated with the nanoparticle size and the existing filler-polymer and ion-dipole interactions.

Designing Carbon Nanotube-Based Oil Absorbing Membranes from Gamma Irradiated and Electrospun Polystyrene Nanocomposites

Carbon-based materials are outstanding candidates for oil spill clean-ups due to their superhydrophobicity, high surface area, chemical inertness, low density, recyclability, and selectivity. The current work deals with the fabrication of membrane oil absorbents based on carbon nanotube (CNT) reinforced polystyrene (PS) nanocomposites by electrospinning technique. The spun membranes are also irradiated with the gamma radiation to induce enough crosslinks and thus good polymer-filler interactions. The structural, morphological, and surface properties in addition to the oil/water separation efficiency were investigated by varying the concentration of CNT and the dose of γ-irradiation. Fabricated nanofiber membranes show superior hydrophobicity and selective oil absorption at 0.5 wt.% of CNT concentration. The best mechanical properties are also obtained at this particular concentration and at 15 KGy optimum γ-irradiation dosage. The gamma irradiated PS/0.5 wt.% CNT membrane also exhibits good antibacterial effects against the bacteria, Escherichia coli, in the form of bacterial inhibition rings around the membranes. The present study thus shows the environmental applicability of the fabricated PS/CNT membranes in treating oil-contaminated water.

Improved Piezoelectric Sensing Performance of P(VDF-TrFE) Nanofibers by Utilizing BTO Nanoparticles and Penetrated Electrodes

Piezoelectric polymers with good flexibility have attracted tremendous attention in wearable sensors and energy harvesters. As the piezoelectricity of polymers such as polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] is lower than that of their ceramic counterparts, various approaches have been employed to improve the piezoelectric output of PVDF-based sensors, such as electrospinning, heat annealing, nanoconfinement, polymer blending, and nanoparticle addition. Here, we report two strategies to improve the piezoelectric sensing performance of polymer-based piezoelectric nanofibers, which include the formation of barium titanate (BTO)/P(VDF-TrFE) composite nanofibers and fabrication of penetrated electrodes to enlarge the interfacial area. BTO/P(VDF-TrFE) nanofibers with a BTO weight fraction of 5 wt % exhibit the maximum β-phase crystallinity and piezoelectricity. The piezoelectric output of the BTO/P(VDF-TrFE) nanofiber mat is significantly improved compared with that of pristine P(VDF-TrFE), which is confirmed by piezoresponse force microscopy (PFM) and compression loading tests. In order to form the penetrated electrodes, oxygen (O₂) plasma treatment is employed, followed by an electroless plating process. The BTO/P(VDF-TrFE) nanofibers with penetrated electrodes demonstrate increased dielectric constants and enhanced piezoelectric outputs. A BTO/P(VDF-TrFE) nanofiber-based sensor with penetrated electrodes is capable of discerning the energy of a free-falling ball as low as 0.6 μJ and sensing the movement of a walking ant.

Synthesis, optimization and applications of ZnO/polymer nanocomposites

Polymer composites have established an excellent position among the technologically essential materials because of their wide range of applications. An enormous research interest has been devoted to zinc oxide (ZnO) based polymer nanocomposites, due to their exceptional electrical, optical, thermal, mechanical, catalytic, and biomedical properties. This article provides a review of various polymer composites consisting of ZnO nanoparticles (NPs) as reinforcements, exhibiting excellent properties for applications such as the dielectric, sensing, piezoelectric, electromagnetic shielding, thermal conductivity and energy storage. The preparation methods of such composites including solution blending, in situ polymerization, and melt intercalation are also explained. The current challenges and potential applications of these composites are provided in order to guide future progress on the development of more promising materials. Finally, a detailed summary of the current trends in the field is presented to progressively show the future prospects for the development of ZnO containing polymer nanocomposite materials.

Fabrication of a polyvinylidene fluoride cactus-like nanofiber through one-step electrospinning

Surface modification of fibers has attracted significant attention in different areas and applications. In this work, polyvinylidene fluoride (PVDF) cactus-like nanofibers were directly produced via electrospinning at a high relative humidity (RH) of 62%. The formation mechanism of the cactus structure was demonstrated. The effects of the RH on the fabrication of the cactus structure, crystalline phases, mechanical properties, hydrophobicity, and piezoelectric properties of the PVDF nanofibers were investigated. The results showed that the cactus-like nanofibers have a high crystallinity (ΔX c), and an outstanding water contact angle (WCA), as well as good electrical outputs. We believe that the PVDF cactus structure can be used in many applications such as energy harvesting and self-cleaning surfaces.

Thermal Properties of TiO₂NP/CNT/LDPE Hybrid Nanocomposite Films

This work aims to investigate the effect of hybrid filler concentration on the thermal stability of low-density polyethylene (LDPE) matrices. LDPE-based composite films were synthesized by melt mixing, followed by compression molding, to study the influence of titanium oxide nanoparticles (TONPs) and/or multi-walled carbon nanotubes (CNTs) on the thermal properties of LDPE matrices. Fourier transform infrared (FTIR) spectroscopy confirmed the slight increase in the band intensities after TONP addition and a remarkable surge after the incorporation of CNTs. The value of crystallization temperature (Tc) was not modified after incorporating TONPs, while an enhancement was observed after adding the hybrid fillers. The melting temperature (Tm) was not changed after introducing the CNTs and CNT/TONP hybrid fillers. The percentage crystallinity (Xc %) was increased by 4% and 6%, after incorporating 1 wt % and 3 wt % CNTs, respectively. The TONP incorporation did not modify the Xc %. Moreover, thermal gravimetric analysis (TGA) thermograms confirmed the increased thermal stability after introducing CNTs and hybrid fillers compared to TONP incorporation.

Dominant Role of Young's Modulus for Electric Power Generation in PVDF⁻BaTiO₃ Composite-Based Piezoelectric Nanogenerator

The electric power output of a piezoelectric nanogenerator (PENG) depends on the various physical parameters of the constituent materials, including the piezoelectric coefficient, Young's modulus, and dielectric constant. Herein, we report the mechanical and electrical properties of a poly(vinylidene fluoride)⁻BaTiO₃ (PVDF⁻BTO) composite-based PENG. Variation of the BTO nanoparticle (NP) content enabled the systematic tuning of the physical parameters that are related to power generation in the composite. The Young's modulus of the PVDF⁻BTO composite initially increased, and then eventually decreased, with the increasing BTO content, which was probably due to the clustering effect of the high modulus BTO NPs. The dielectric constant of the composite continuously increased as the BaTiO₃ content increased. The piezoelectric outputs were greatly enhanced at 10 wt% of BTO, where the Young's modulus was the highest. These results indicate that the Young's modulus plays an important role in the piezoelectric power generation of the composite-based PENGs.

Stable and High Piezoelectric Output of GaN Nanowire-Based Lead-Free Piezoelectric Nanogenerator by Suppression of Internal Screening

A piezoelectric nanogenerator (PNG) that is based on c-axis GaN nanowires is fabricated on flexible substrate. In this regard, c-axis GaN nanowires were grown on GaN substrate using the vapor-liquid-solid (VLS) technique by metal organic chemical vapor deposition. Further, Polydimethylsiloxane (PDMS) was coated on nanowire-arrays then PDMS matrix embedded with GaN nanowire-arrays was transferred on Si-rubber substrate. The piezoelectric performance of nanowire-based flexible PNG was measured, while the device was actuated using a cyclic stretching-releasing agitation mechanism that was driven by a linear motor. The piezoelectric output was measured as a function of actuation frequency ranging from 1 Hz to 10 Hz and a linear tendency was observed for piezoelectric output current, while the output voltages remained constant. A maximum of piezoelectric open circuit voltages and short circuit current were measured 15.4 V and 85.6 nA, respectively. In order to evaluate the feasibility of our flexible PNG for real application, a long term stability test was performed for 20,000 cycles and the device performance was degraded by less than 18%. The underlying reason for the high piezoelectric output was attributed to the reduced free carriers inside nanowires due to surface Fermi-level pinning and insulating metal-dielectric-semiconductor interface, respectively; the former reduced the free carrier screening radially while latter reduced longitudinally. The flexibility and the high aspect ratio of GaN nanowire were the responsible factors for higher stability. Such higher piezoelectric output and the novel design make our device more promising for the diverse range of real applications.