Ionic Thermoelectric Generators in Vertical and Planar Topologies Based on Fluorinated Polymer Hybrid Materials with Ionic Liquids

Ionic thermoelectrics (TEs), in which voltage generation is based on ion migration, are suitable for applications based on their low cost, high flexibility, high ionic conductivity, and wide range of Seebeck coefficients. This work reports on the development of ionic TE materials based on the poly(vinylidene fluoride-trifluoroethylene), Poly(VDF-co-TrFE), as host polymer blended with different contents of the ionic liquid, IL, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI]. The morphology, physico-chemical, thermal, mechanical, and electrical properties of the samples are evaluated together with the TE response. It is demonstrated that the IL acts as a nucleating agent for polymer crystallization. The mechanical properties and ionic conductivity values are dependent on the IL content. A high room temperature ionic conductivity of 0.008 S cm-1 is obtained for the sample with 60 wt% of [EMIM][TFSI] IL. The TE properties depend on both IL content and device topology-vertical or planar-the largest generated voltage range being obtained for the planar topology and the sample with 10 wt% of IL content, characterized by a Seebeck coefficient of 1.2 mV K-1. Based on the obtained maximum power density of 4.9 µW m-2, these materials are suitable for a new generation of TE devices.

Dual Interface Compatibility Enabled via Composite Solid Electrolyte with High Transference Number for Long-Life All-Solid-State Lithium Metal Batteries

The development of solid-state electrolytes (SSEs) effectively solves the safety problem derived from dendrite growth and volume change of lithium during cycling. In the meantime, the SSEs possess non-flammability compared to conventional organic liquid electrolytes. Replacing liquid electrolytes with SSEs to assemble all-solid-state lithium metal batteries (ASSLMBs) has garnered significant attention as a promising energy storage/conversion technology for the future. Herein, a composite solid electrolyte containing two inorganic components (Li6.25Al0.25La3Zr2O12, Al2O3) and an organic polyvinylidene difluoride matrix is designed rationally. X-ray photoelectron spectroscopy and density functional theory calculation results demonstrate the synergistic effect among the components, which results in enhanced ionic conductivity, high lithium-ion transference number, extended electrochemical window, and outstanding dual interface compatibility. As a result, Li||Li symmetric battery maintains a stable cycle for over 2500 h. Moreover, all-solid-state lithium metal battery assembled with LiNi0.6Co0.2Mn0.2O2 cathode delivers a high discharge capacity of 168 mAh g-1 after 360 cycles at 0.1 C at 25 °C, and all-solid-state lithium-sulfur battery also exhibits a high initial discharge capacity of 912 mAh g-1 at 0.1 C. This work demonstrates a long-life flexible composite solid electrolyte with excellent interface compatibility, providing an innovative way for the rational construction of next-generation high-energy-density ASSLMBs.

Synthetic strategy for the production of electrically polarized polyvinylidene fluoride-trifluoroethylene-co-polymer osseo-functionalized with hydroxyapatite scaffold

The physiological mechanism of bone tissue regeneration is intricately organized and involves several cell types, intracellular, and extracellular molecular signaling networks. To overcome the drawbacks of autografts and allografts, a number of synthetically produced scaffolds have been manufactured by integrating ceramics, polymers, and their hybrid-composites. Considering the fact that natural bone is composed primarily of collagen and hydroxyapatite, ceramic-polymer composite materials seem to be the most viable alternative to bone implants. Here, in this experimental study, copolymer PVDF-TrFE has been amalgamated with HA ceramics to produce composite scaffolds as bone implants. In order to fabricate PVDF-TrFE-HA (polyvinylidene fluoride-trifluoroethylene-hydroxyapatite) composite scaffolds, solvent casting-particulate leaching technique was devised. Two scaffold specimens were produced, with different PVDF-TrFE and HA molar ratios (70:30 and 50:50), and then electrically polarized to observe the subsequent polarization impact on the tissue growth and the suppression of bacterial cell proliferation. Both the specimens underwent characterization to analyze their biocompatibility and bactericidal activities. The bacterial culture of Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus) bacteria on the composites was studied to understand the antibacterial characteristics. Moreover, MG63 cells cultured on these as-formed composites provided information about osteogenesis. Improved osteogenesis and antibacterial efficacy were observed on both the composites. However, the composite with 70 wt% PVDF-TrFE and 30 wt% HA showed a higher bactericidal effect as well as osteogenesis. It was found that PVDF-TrFE-HA-based biomaterials have the potential for bone tissue engineering applications.

A PEGylated PVDF Antifouling Membrane Prepared by Grafting of Methoxypolyethylene Glycol Acrylate in Gama-Irradiated Homogeneous Solution

In this study, methoxypolyethylene glycol acrylate (mPEGA) served as a PEGylated monomer and was grafted onto polyvinylidene fluoride (PVDF) through homogeneous solution gamma irradiation. The grafting process was confirmed using several techniques, including infrared spectroscopy (FTIR), thermodynamic stability assessments, and rotational viscosity measurements. The degree of grafting (DG) was determined via the gravimetric method. By varying the monomer concentration, a range of DGs was achieved in the PVDF-g-mPEGA copolymers. Investigations into water contact angles and scanning electron microscopy (SEM) images indicated a direct correlation between increased hydrophilicity, membrane porosity, and higher DG levels in the PVDF-g-mPEGA membrane. Filtration tests demonstrated that enhanced DGs resulted in more permeable PVDF-g-mPEGA membranes, eliminating the need for pore-forming agents. Antifouling tests revealed that membranes with a lower DG maintained a high flux recovery rate, indicating that the innate properties of PVDF could be largely preserved.

3D-Printed piezoelectric nanogenerator with aligned graphitic carbon nitrate nanosheets for enhancing piezoelectric performance

Carbon-based materials are attracting increasing attention in the field of electronic devices because of their nontoxicity, availability, low cost, and easy synthesis. In this study, we fabricated a printed piezoelectric nanogenerator (PENG) based on a Polyvinylidene fluoride (PVDF) and graphitic carbon nitrate (g-C3N4) composite. Piezoelectric films with different weight percentages (0, 5, 7.5, 10, and 15 wt%) of g-C3N4 nanosheets (CNNSs) were fabricated. The PVDF/CNNS with 7.5% CNNS exhibited higher performance. We observed that the printing process aligned all CNNS along the x-axis, which improved stress management and eventually improved the performance of the fabricated device. The fabricated device exhibited better performance without pooling and generated a peak-to-peak voltage of 6.65 V with a current of 0.195 µA, corresponding to a power density of 4.86 µW/cm2. The device generated a voltage of up to 18.8 V with footsteps.

PVDF Nanofiber Modified with ZnO Nanowires/Polydopamine for the Treatment of Sewage Containing Heavy Metals, Organic Dyes, and Bacteria

In various countries worldwide, the issue of wastewater contamination poses a significant threat due to its intricate composition of heavy metals, organic dyes, and microorganisms, thereby complicating the purification process. Consequently, researchers have expressed considerable interest in materials capable of eliminating organic, heavy metal, and microbial pollutants. This study focuses on the fabrication of a water purification membrane (PDA/ZnO-NWs/PVDF) with a hierarchical structure and the ability to remove multiple pollutants. The membrane was created by modifying poly(vinylidene fluoride) (PVDF) nanofiber with zinc oxide nanowires (ZnO-NWs) and reinforcing it with polydopamine (PDA). The experimental results demonstrate that the PDA/ZnO-NWs/PVDF membrane exhibits a range of functionalities, including long-lasting superhydrophilicity, Cu(II) adsorption, photocatalytic degradation, and antibacterial ability. The manipulation of the DA synthesis procedure allows for the adjustment of the wettability, adsorption, and photocatalytic and antibacterial activities of the PDA/ZnO-NWs/PVDF composite. According to the Langmuir isotherm, the maximum Cu(II) adsorption capacity of the PDA/ZnO-NWs/PVDF membrane is determined to be 65.75 mg/g, which is significantly higher (27.26 mg/g) than that of the ZnO-NWs/PVDF membrane (38.49 mg/g). The PDA/ZnO-NWs/PVDF composite exhibited a notable degradation capacity toward rhodamine B under natural sunlight, reaching a maximum of 5.97 mg/g. Additionally, the degradation rate achieved during daylight hours was as high as 90.42%. Furthermore, the antibacterial efficacy of the PDA/ZnO-NWs/PVDF composite against both Gram-positive and Gram-negative bacteria approached 100%. This work presents a promising approach for the treatment of wastewater containing various coexisting contaminants.

Amplified Dielectric Properties of PVDF-HFP/SrTiO3 Nanocomposites for a Flexible Film Capacitor

A simple solution casting technique was used to fabricate perovskite strontium titanate (SrTiO3)-loaded poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) nanocomposite films for efficient energy storage applications. Various microscopic and spectroscopic methods were used to study the characteristics of the polymer nanocomposite films, like Fourier transform infrared spectroscopy (FTIR), X-ray diffraction technique (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible spectroscopy, thermogravimetric analysis, and mechanical tensile test (stress vs strain). The FTIR, XRD, and FESEM analyses confirmed the incorporation and proper dispersion of SrTiO3 nanoparticles in the PVDF-HFP polymer matrix. An improvement in the optical, thermal, and mechanical behavior of the nanocomposite film was observed compared to the pure polymer. The values of dielectric constant, loss tangent, and AC conductivity of pure PVDF-HFP polymer and PVDF-HFP/SrTiO3 nanocomposites (2, 6, and 10 wt % SrTiO3 loadings) were analyzed in a temperature and frequency span of 30-150 °C and 1-100 kHz, respectively. To better understand the electrical properties of the materials, Nyquist plots were generated, and their related circuit designs were fitted. The 2 wt % SrTiO3 loaded nanocomposite exhibited the highest dielectric enhancement and AC conductivity compared to higher filler-loaded nanocomposites. This exceptional dielectric enhancement at very small filler loading is beneficial for commercialization and economically viable for real-time applications.

Facile assembly of flexible quaternary SnO2/SrSnO3/Fe3O4/PVDF nanocomposites with tunable optical, electrical, and magnetic properties for promising magneto-optoelectronic applications

Facile assembly, co-precipitation, and drop casting procedures have been used to construct SnO₂/SrSnO₃/Fe₃O₄/PVDF flexible nanocomposites. SnO₂/SrSnO₃/Fe₃O₄ nanocomposites (TSF NCs') have been successfully incorporated into polyvinylidene fluoride polymers (PF), according to the microstructural exploration of the systems, which was revealed by XRD, EDX, and ATR-FTIR analysis. The FESEM and cross-section areas demonstrated that the addition of TSF NCs' to PF porous material enhanced its surface characteristics and decreased its surface roughness. The optical gap was lowered from 3.90 to 3.07 eV, and it was discovered that both the refractive index and optical conductivity had improved when TSF NCs' were incorporated into PF. According to the observations, the supplement ratios have a profound influence on the dielectric properties of the nanocomposites. Moreover, the electrical parameters of TSF/PF nanocomposite are significantly modified. The TSF/PF magnetic nanocomposite has good magnetic reactivity and can be easily extracted from the aqueous solution using an external magnetic field, as demonstrated by VSM. This research has been conducted to obtain TSF/PF nanocomposites to be used in promising magno-optoelectronic applications.

Surface modification of polyether ether ketone implant with a novel nanocomposite coating containing poly (vinylidene fluoride) toward improving piezoelectric and bioactivity performance

Polyether ether ketone (PEEK) is an appropriate biomaterial for orthopedic implant applications due to its superior mechanical properties, chemical resistance, nontoxicity, and Magnetic resonance imaging (MRI) compatibility. Unfortunately, the inherent bio-inertness of PEEK restricted its application and required some modification to provide better bioactivity. Besides it, the generated electrical signals in the bone due to its piezoelectricity features have a vital role in regulating bone repair and regeneration. We aimed to modify the surface of PEEK with a dual-functionality nanocomposite that provides surface bioactivity and simulates the piezoelectricity of bone. So, we introduced a novel piezoelectric-bioactive nanocomposite of dispersed poly (vinylidene fluoride) (PVDF) in a sulfonated PEEK (SPEEK) matrix containing Nanohydroxyapatite (nHA) and Carbon nanofiber (CNF) fillers for coating on PEEK substrate to improve its biological activity and simulate the electrical microenvironment for bone tissue. Furthermore, sulfonation of the PEEK surface was conducted as an intermediate layer to prepare better adhesion between the coating nanocomposite and the PEEK sublayer. Surface and cross-section morphology, apatite formation, and cell attachment were investigated on the different treated PEEK surfaces using field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). Also, piezoelectric performance, electrical conductivity, contact angle, and mechanical properties were examined on the prepared samples. Moreover, cell viability and cell morphology were investigated for biological evaluation with human osteoblast-like MG-63 cells. Collectively, the hydrophilicity of modified PEEK (mPEEK) coated with nanocomposite was improved due to the synergistic effects of SPEEK functional groups and nHA. Also, comprehensive investigation on the mPEEK treated with nanocomposite indicated a noticeably better bone-like apatite formation, cell proliferation, and cell attachments in the presence of nHA. The transfer of induced piezoelectric charges from dispersed PVDF in the matrix to the surface of nanocomposite containing 2 wt% of CNF increased output voltage to 1893 mV. On the other hand, the presence of CNF in nanocomposites enhanced tensile strength and Young's modulus by 92% and 117%, respectively.

Electroactive CTAB/PVDF composite film based photo-rechargeable hybrid power cell for clean energy generation and storage

Herein, electroactive polymer based photo-induced hybrid power cell has been developed using CTAB/PVDF composite film in a sustainable manner. First high dielectric polymer film has been prepared by doping CTAB in PVDF matrix via solution casting method. In the basic configuration of this hybrid power cell, aqueous electrolyte solution of PVA-MnO₂-Eosin Y has been utilized as solar light absorber and photo-electron generator whereas the high dielectric CTAB/PVDF (~ 400) is used as dielectric separator cum storage part in a very transparent way. The cell shows maximum voltage [Formula: see text] 1.1 V with short-circuit current density ~ 7.83 mA/cm² under ~ 110 mW/cm² normal light illumination. The device reveal almost same performance for a long time (30 days). The high storage impact of the hybrid cell is investigated by its promising conversion efficiency [Formula: see text] with energy density and power density [Formula: see text] mWh/m² and [Formula: see text] 5.5 W/m² respectively.

Approaches for Management and Valorization of Non-Homogeneous, Non-Recyclable Plastic Waste

The environmental accumulation of plastic wastes has become one of the most discussed topics in the scientific community. The development of new strategies to tackle this issue is of crucial importance, and different approaches are being investigated to effectively reduce plastic waste generated by improper or inefficient disposal. In addition to the efforts addressing the development of biodegradable plastics, the research is currently focused on the development of innovative recycling approaches. Indeed, although most plastic materials are potentially recyclable, only 15% of the worldwide plastic waste is currently recycled, while the remaining 85% is usually incinerated to recover thermal energy or landfilled. The hurdles to efficient recycling come from improper management of end-of-life plastic goods. Moreover, the highly heterogeneous nature and versatility of plastic and polymeric materials have led to the development of multilayered materials, composites, blends and many other different species, whose management and/or reprocessing to yield high-value products is extremely challenging. Thus, although these materials are extremely valuable from an industrial point of view, they add a high degree of complexity to the recycling process because each one of them is different from the other, but they cannot be separated efficiently. The aim of the present review is to return a comprehensive overview of environmental and management issues related to the complex and heterogeneous mixture of plastic waste that is generated at the end of the sorting procedures in Italian plastic recycling plants, the so-called 'Plasmix'. This review lists the difficulties and limitations related to the management of non-recyclable Plasmix and highlights the strategies for the proper, sustainable and valuable use of this plastic waste.

Electrospray Deposition of Polyvinylidene Fluoride (PVDF) Microparticles: Impact of Solvents and Flow Rate

Polymeric microparticles have been shown to have great impacts in the area of drug delivery, biosensing, and tissue engineering. Electrospray technology, which provides a simple yet effective technique in the creation of microparticles, was utilized in this work. In addition, altering the electrospray experimental parameters such as applied voltage, flow rate, collector distance, solvents, and the polymer-solvent mixtures can result in differences in the size and morphology of the produced microparticles. The effects of the flow rate at (0.15, 0.3, 0.45, 0.6, 0.8, and 1 mL/h) and N, N-Dimethylformamide (DMF)/acetone solvent ratios (20:80, 40:60, 60:40, 80:20, 100:0 v/v) in the production of polyvinylidene fluoride (PVDF) microparticles were studied. Scanning electron microscopy (SEM) was used to observe changes in the morphology of the microparticles, and this revealed that a higher acetone to DMF ratio produces deformed particles, while flow rates at (0.3 and 0.45 mL/h) and a more optimized DMF to acetone solvent ratio (60:40 v/v) produced uniform spherical particles. We discovered from the Raman spectroscopy results that the electrosprayed PVDF microparticles had an increase in piezoelectric β phase compared to the PVDF pellet used in making the microparticles, which in its original form is α phase dominant and non-piezoelectric.

Suitable Cathode NMP Replacement for Efficient Sustainable Printed Li-Ion Batteries

N-methyl-2-pyrrolidone (NMP) is the most common solvent for manufacturing cathode electrodes in the battery industry; however, it is becoming restricted in several countries due to its negative environmental impact. Taking into account that ∼99% of the solvent used during electrode fabrication is recovered, dimethylformamide (DMF) is a considerable candidate to replace NMP. The lower boiling point and higher ignition temperature of DMF lead to a significant reduction in the energy consumption needed for drying the electrodes and improve the safety of the production process. Additionally, the lower surface tension and viscosity of DMF enable improved current collector wetting and higher concentrations of the solid material in the cathode slurry. To verify the suitability of DMF as a replacement for NMP, we utilized screen printing, a fabrication method that provides roll-to-roll compatibility while allowing controlled deposition and creation of sophisticated patterns. The battery systems utilized NMC (LiNi _x Mn _y Co _z O₂) chemistry in two configurations: NMC523 and NMC88. The first, well-established NCM523, was used as a reference, while NMC88 was used to demonstrate the potential of the proposed method with high-capacity materials. The cathodes were used to create coin and pouch cell batteries that were cycled 1000 times. The achieved results indicate that DMF can successfully replace NMP in the NMC cathode fabrication process without compromising battery performance. Specifically, both the NMP blade-coated and DMF screen-printed batteries retained 87 and 90% of their capacity after 1000 (1C/1C) cycles for NMC523 and NMC88, respectively. The modeling results of the drying process indicate that utilizing a low-boiling-point solvent (DMF) instead of NMP can reduce the drying energy consumption fourfold, resulting in a more environmentally friendly battery production process.

Investigation of molecular mechanisms of polyvinylidene fluoride under the effects of temperature, electric poling, and mechanical stretching using molecular dynamics simulations

This study uses molecular dynamics (MD) simulations to investigate the molecular mechanisms of polyvinylidene fluoride (PVDF) influenced by temperature, electric poling, and mechanical stretching. The β-phase, with all-trans ⟨T⟩ planar zigzag conformation, is known to have the best potential of energy harvesting, while α-phase, with alternating trans ⟨T⟩ and gauche ⟨G⟩ linkages, is more stable in terms of potential energy. By applying an electric field and uniaxial deformation to an amorphous PVDF system, we study the transformation from α- to β-phase and corresponding molecular mechanisms by tracking the molecular chain conformation using the trans percentages (P_T). After complete relaxation of molecular chains, the chain conformations and P_T values indicate a typical distribution pattern of α-phase. Next, we observe that the dipole moment of the system increases significantly with the presence of a strong electric field without immediately affecting the chain conformations. The increment of dipole moment is due to the aligning of side atoms within the chains and the increment becomes more significant with elevated temperature. In contrast, chain conformations change significantly under mechanical stretching. Specifically, before yielding, the total dipole moments are still governed by local orientations of atoms. Later, the chain segments begin to straighten in the large deformation stage, which leads to the increment of the total dipole moment. Our results also show that there exists an optimal temperature window for maximum ⟨G⟩ to ⟨T⟩ transformation rate. Moreover, we look into the synergistic effect of electric poling and mechanical stretching and explain molecular-level mechanisms for this effect. This study contributes to the fundamental understanding of the underlying molecular mechanisms for the piezoelectric PVDF system under different processing conditions.

Enhancement of triboelectricity based on fully organic composite films with a conducting polymer

Triboelectric nanogenerators (TENGs) based on ferroelectric organic materials have advantages of high flexibility, biocompatibility, controllable ferroelectric properties, etc. However, this has limited the electrical output performance due to their lower ferroelectric characteristics than those of inorganic ferroelectric materials. A lot of effort has been made to improve the organic ferroelectric characteristics through composites, surface modifications, structures, etc. Herein, we report TENGs made of ferroelectric composite materials consisting of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The composite was prepared by simply blending PVDF-TrFE and PEDOT:PSS with a weight ratio from 0% to 60%. When the ratio was 20%, the ferroelectric-crystalline phase was enhanced and the highest dielectric constant was observed. Accordingly, the TENGs consisting of 20% composite film and polyimide exhibited the best output performance: the maximum open circuit voltage and short circuit current were ∼15 V and ∼2.3 μA at 1 Hz oscillation, respectively. These results indicate that the ferroelectric characteristics of PVDF-TrFE can be enhanced by adding PEDOT:PSS as a nanofiller.

Nanofiber-Based Substrate for a Triboelectric Nanogenerator: High-Performance Flexible Energy Fiber Mats

Flexible and stretchable triboelectric nanogenerators (TENGs) are the next-generation systems for wearable and portable electronics. In this study, we have demonstrated an all nanofiber-based TENG for energy harvesting and biomechanical sensing applications. The TENG was prepared using the Forcespinning (FS) method to produce poly(vinylidene fluoride) (PVDF) and thermoplastic polyurethane (TPU) nanofiber (NF) membranes. The TPU nanofiber membranes were interfaced with a homogeneously sputtered gold nanofilm. The experimental characterization of the PVDF-TPU/Au NF-TENG revealed that surface interfaced with dispersed gold in a TPU fiber membrane produced a maximum open-circuit voltage of 254 V and a short-circuit current of 86 μA output at a 240 bpm load frequency, which was, respectively, 112 and 87% greater than bare PVDF-TPU NF-based TENG. All systems were composed of an active contact surface area of 3.2 × 2.5 cm². Furthermore, the TENG was able to light up 75 LEDs (1.5 V of each) by the hand-tapping motion. The resistive load and capacitor test results exemplified a TENG offering a simple and high-performance self-chargeable device. Furthermore, we have tested the TENG's response for biomechanical movements at different frequencies, suggesting the TENG's potential to be also used as a cost-effective self-powered flexible body motion sensor.

Effect of Polymer Dissolution Temperature and Conditioning Time on the Morphological and Physicochemical Characteristics of Poly(Vinylidene Fluoride) Membranes Prepared by Non-Solvent Induced Phase Separation

This work reports on the production of poly(vinylidene fluoride) (PVDF) membranes by non-solvent induced phase separation (NIPS) using N,N-dimethylformamide (DMF) as solvent and water as non-solvent. The influence of the processing conditions in the morphology, surface characteristics, structure, thermal and mechanical properties were evaluated for polymer dissolution temperatures between 25 and 150 °C and conditioning time between 0 and 10 min. Finger-like pore morphology was obtained for all membranes and increasing the polymer dissolution temperature led to an increase in the average pore size (≈0.9 and 2.1 µm), porosity (≈50 to 90%) and water contact angle (up to 80°), in turn decreasing the β PVDF content (≈67 to 20%) with the degree of crystallinity remaining approximately constant (≈56%). The conditioning time did not significantly affect the polymer properties studied. Thus, the control of NIPS parameters proved to be suitable for tailoring PVDF membrane properties.

In Vitro Effect of Replicated Porous Polymeric Nano-MicroStructured Biointerfaces Characteristics on Macrophages Behavior

In the last decades, optimizing implant properties in terms of materials and biointerface characteristics represents one of the main quests in biomedical research. Modifying and engineering polyvinylidene fluoride (PVDF) as scaffolds becomes more and more attractive to multiples areas of bio-applications (e.g., bone or cochlear implants). Nevertheless, the acceptance of an implant is affected by its inflammatory potency caused by surface-induced modification. Therefore, in this work, three types of nano-micro squared wells like PVDF structures (i.e., reversed pyramidal shape with depths from 0.8 to 2.5 microns) were obtained by replication, and the influence of their characteristics on the inflammatory response of human macrophages was investigated in vitro. FTIR and X-ray photoelectron spectroscopy analysis confirmed the maintaining chemical structures of the replicated surfaces, while the topographical surface characteristics were evaluated by AFM and SEM analysis. Contact angle and surface energy analysis indicated a modification from superhydrophobicity of casted materials to moderate hydrophobicity based on the structure’s depth change. The effects induced by PVDF casted and micron-sized reversed pyramidal replicas on macrophages behavior were evaluated in normal and inflammatory conditions (lipopolysaccharide treatment) using colorimetric, microscopy, and ELISA methods. Our results demonstrate that the depth of the microstructured surface affects the activity of macrophages and that the modification of topography could influence both the hydrophobicity of the surface and the inflammatory response.

Phase Transitions in Poly(vinylidene fluoride)/Polymethylene-Based Diblock Copolymers and Blends

The crystallization and morphology of two linear diblock copolymers based on polymethylene (PM) and poly(vinylidene fluoride) (PVDF) with compositions PM23-b-PVDF77 and PM38-b-PVDF62 (where the subscripts indicate the relative compositions in wt%) were compared with blends of neat components with identical compositions. The samples were studied by SAXS (Small Angle X-ray Scattering), WAXS (Wide Angle X-ray Scattering), PLOM (Polarized Light Optical Microscopy), TEM (Transmission Electron Microscopy), DSC (Differential Scanning Calorimetry), BDS (broadband dielectric spectroscopy), and FTIR (Fourier Transform Infrared Spectroscopy). The results showed that the blends are immiscible, while the diblock copolymers are miscible in the melt state (or very weakly segregated). The PVDF component crystallization was studied in detail. It was found that the polymorphic structure of PVDF was a strong function of its environment. The number of polymorphs and their amount depended on whether it was on its own as a homopolymer, as a block component in the diblock copolymers or as an immiscible phase in the blends. The cooling rate in non-isothermal crystallization or the crystallization temperature in isothermal tests also induced different polymorphic compositions in the PVDF crystals. As a result, we were able to produce samples with exclusive ferroelectric phases at specific preparation conditions, while others with mixtures of paraelectric and ferroelectric phases.

Enhanced Piezoelectric Performance of Various Electrospun PVDF Nanofibers and Related Self-Powered Device Applications

The piezoelectric polymer poly(vinylidene fluoride) (PVDF) has been widely employed for energy harvesting or sensors. Its piezoelectricity originates from the unique crystal structure and the oriented electric dipoles. Generally, electrospinning (ES) is able to improve the crystallinity and piezoelectricity of PVDF. In this investigation, three types of ES, including far-field ES with random (R-PVDF-FFES) or aligned distribution (A-PVDF-FFES) and near-field ES (PVDF-NFES), are applied to fabricate a one-step polarized PVDF membrane. To compare the piezoelectricity of separated PVDF-NFES fibers, the array of PVDF-NFES fibers is encapsulated in polylactic acid (PLA). The result shows that the piezoelectricity of PVDF is dramatically enhanced by NFES and FFES. In d₃₁ mode, the current density of PVDF-NFES-PLA is 75.63 pA cm^-2 with a 2 Hz shear force, which is four times larger than A-PVDF-FFES (17.62 pA cm^-2) or seven times larger than R-PVDF-FFES (10.63 pA cm^-2). Due to its outstanding property, the PVDF-NFES-PLA membrane is designed to be applied as a self-powered device. The unimorph cantilevers are prepared to harvest the vibration energy and their output power density reaches 95.3 μW m^-2 at a resonance frequency of 31 Hz. Meanwhile, the flexible bending sensor and pressure sensor are fabricated with a PVDF-NFES-PLA membrane, which shows the stable response for pressure with sensitivity values of 864.68 and 22.6 mV kPa^-1, respectively.

Fabrication and Characterization of Non-Equilibrium Plasma-Treated PVDF Nanofiber Membrane-Based Sensors

The effect of a self-pulsing non-equilibrium plasma discharge on piezoelectric PVDF nanofiber membrane was investigated. The plasma discharge was generated in air with a DC power source, with a discharge current of 0.012 mA, a nominal interelectrode separation of 1 mm, and discharge voltage of ~970 V. In a continuous fabrication process, the electrospinning method was used to generate thin nanofiber membrane with a flow rate of 0.7-1 mL h^-1 and 25-27 kV voltage to obtain the nanofiber with high sensitivity and a higher degree of alignment and uniformity over a larger area. Plasma treatment was applied on both single layer and multi-layer (three layers) nanomembranes. In addition, simultaneously, the nanofiber membranes were heat-treated at a glass transition temperature (80-120 °C) and then underwent plasma treatment. Fourier-transform infrared (FTIR) spectroscopy showed that the area under the curve at 840 and 1272 cm^-1 (β phase) increased due to the application of plasma and differential scanning calorimeter (DSC) indicated an increase in the degree of crystallinity. Finally, PVDF sensors were fabricated from the nanofibers and their piezoelectric properties were characterized. The results suggested that compared to the pristine samples the piezoelectric properties in the plasma and plasma-heat-treated sensors were enhanced by 70% and 85% respectively.

Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d33 = -1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF.

Kinetics and thermodynamic studies of Methyl Orange removal by polyvinylidene fluoride-PEDOT mats

We report the preparation of poly(3,4-ethylene dioxythiophene) (PEDOT)-modified polyvinylidene fluoride electrospun fibers and their use as a novel adsorbent material for the removal of the anionic dye Methyl Orange (MO) from aqueous media. This novel adsorbent material can be used to selectively remove MO on a wide pH range (3.0-10.0), with a maximum capacity of 143.8 mg/g at pH 3.0. When used in a recirculating filtration system, the maximum absorption capacity was reached in a shorter time (20 min) than that observed for batch mode experiments (360 min). Based on the analyses of the kinetics and adsorption isotherm data, one can conclude that the predominant mechanism of interaction between the membrane and the dissolved dye molecules is electrostatic. Besides, considering the estimated values for the Gibbs energy, and entropy and enthalpy changes, it was established that the adsorption process is spontaneous and occurs in an endothermic manner. The good mechanical and environmental stability of these membranes allowed their use in at least 20 consecutive adsorption/desorption cycles, without significant loss of their characteristics. We suggest that the physical-chemical characteristics of PEDOT make these hybrid mats a promising adsorbent material for use in water remediation protocols and effluent treatment systems.

Suppressing loss tangent with significantly enhanced dielectric permittivity of poly(vinylidene fluoride) by filling with Au-Na1/2Y1/2Cu3Ti4O12 hybrid particles

Three-phase gold nanoparticle–Na_1/2Y_1/2Cu₃Ti₄O₁₂ (Au–NYCTO)/poly(vinylidene fluoride) (PVDF) composites with 0.095–0.487 hybrid particle volume fractions (f) were fabricated. Au nanoparticles with a diameter of ∼10 nm were decorated on the surfaces of high-permittivity NYCTO particles using a modified Turkevich's method. The polar β-PVDF phase was confirmed to exist in the composites. Significantly enhanced dielectric permittivity of ∼98 (at 1 kHz) was obtained in the Au–NYCTO/PVDF composite with f_Au–NYCTO = 0.487, while the loss tangent was suppressed to 0.09. Abrupt changes in the dielectric and electrical properties, which signified percolation behavior, were not observed even when f_Au–NYCTO = 0.487. Using the effective medium percolation theory model, the percolation threshold (f_c) was predicted to be at f_Au–NYCTO = 0.69, at which f_Au was estimated to ∼0.19 and close to the theoretical f_c value for the conductor–insulator composites (f_c = 0.16). A largely enhanced dielectric response in the Au–NYCTO/PVDF composites was contributed by the interfacial polarization effect and a high permittivity of the NYCTO ceramic filler. Au nanoparticles can produce the local electric field in the composites, making the dipole moments in the β-PVDF phase and NYCTO particles align with the direction of the electric field.

Three-phase gold nanoparticle–Na_1/2Y_1/2Cu₃Ti₄O₁₂ (Au–NYCTO)/poly(vinylidene fluoride) (PVDF) composites with 0.095–0.487 hybrid particle volume fractions (f) were fabricated.

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.