Polyvinylidene Fluoride Surface Research Articles

Controlling polydopamine deposition morphology on the surface of poly(vinylidene fluoride) microfiltration membranes for improved oil-water filtration performance

Herein, we studied the effect of adding into water-dopamine mixture a small amount of the fourth generation of bis-MPA based Boltorn™ hyperbranched polyol polyester (H40) or inorganic nanolayered compound MXene on the development of polydopamine (PDA) coating morphology on the surface of polyvinylidene fluoride (PVDF) microfiltration membranes targeting to further enhance their oil fouling resistance and oil-in-water (O/W) filtration performance. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray (EDX), Atomic Force Microscopy (AFM), and Water Contact Angle (WCA) techniques were used for characterization of the modified surfaces. The pure water and (O/W) tight emulsion filtration testing was conducted using a custom-made dead-end filtration setup. It was shown that in the case of dopamine only treatment, the formed on the surface PDA coating largely showed a planar, homogeneous growth which tended to envelope not only the membrane surface irregularities but also the pores thus greatly reducing their size and compromising the permeate flux despite significantly improved surface hydrophilicity. Adding either MXene or H40 into water-dopamine mixture rendered a beneficial effect on the membrane oil fouling resistance and permeation/filtration characteristics. The most spectacular, a hitherto not reported effect was observed after adding into water-dopamine mixture the H40 polymer. In contrast to the planar PDA deposition, the coating morphology in this case consisted of fused together tiny PDA clumps. The ‘clumpy’ PDA coating made less pore blockage and the membranes demonstrated many times greater flux either for pure water or emulsion permeate than after using dopamine only or dopamine with MXene treatments while continued to exhibit oleophobic behavior and high resistance to oil fouling over multiple filtration cycles. The potential nucleating role of this hyperbranched polymer in the development of the PDA clumps is discussed.

Preparation of PVDF-nSiO2/PVSQ high-flux composite membrane by chemical grafting and separation of composite brine by membrane distillation

The large-scale application of membrane distillation (MD), an important method for desalting seawater, is limited due to membrane fouling. In this study, ethyl orthosilicate (TEOS) was polymerized to obtain different nSiO2 particles. Vinyl triethoxysilane (VTES) was hydrolysed and polycondensation was used to produce spherical polyethylene-sesquioxane (PVSQ) microparticles, which were modified to construct micro/nano particles. Then grafted on the surface of polyvinylidene fluoride (PVDF) composite membrane. The low-surface-energy hydrophobic groups present on the surfaces of the vinyl and ethoxy particles greatly enhanced the membrane hydrophobicity. The particle size of nSiO2 can change the properties of the membrane. The separation performance of the membrane was tested by direct contact membrane distillation (DCMD). In the separation of a constant concentration of feed solution (3.5wt% NaCl), the membrane flux was relatively stable at 23.8kg·m−2·h−1, and the salt interception rate reached 99.99%. In the subsequent separation of a salt/humic acid solution, the flux remained stable and the good anti-fouling performance indicating that this system outperformed the unmodified membrane. Finally, the effect of different cations on the water diffusivity was studied using a molecular simulation method. Both Ca2+ and Mg2+ reduced the diffusion coefficient of water. However, when these two ions were present simultaneously, Ca2+ inhibited the binding of Mg2+ to water, and the diffusion coefficient of water increased. This study provides a novel approach for preparing hydrophobic membranes for the separation of complex brines.

Construction of robust DA@CNTs/CS hydrogel coatings on hydrophobic PVDF membrane by deposition of self-assembly for efficient separation of oil-water emulsion and dye wastewater

With the rapid development of industry, the problem of water pollution has become increasingly serious. Though there are many separation materials available to solve this problem, how to separate multiple wastewater at the same time remains a challenge. Hydrogel coating is suitable for use in the field of oil–water separation, and chitosan (CS) is effective in removing anionic dyes. Therefore, the preparation of separation membranes with hydrogel coating containing CS and dopamine (DA) can effectively separate oil–water emulsion and anionic dye wastewater. In this paper, DA@CNTs/CS hydrogel coating was prepared by sequentially coating Cu2+, DA@CNTs, Cu2+ and CS on the surface of polyvinylidene fluoride (PVDF) membrane by deposition of self-assembly, which enhanced the hydrophilicity of the membrane and made it highly underwater oleophobic and antifouling. The alkali treated PVDF membrane contained a large amount of –OH, Cu2+, which formed coordination bonds with –OH, CS, and DA and the hydrogel coating could be stably loaded on the membrane. In addition, the introduction of rigid CNTs effectively improved the performance of the modified membrane under extreme conditions such as high pH and high salt concentration. PVDF-DA@CNTs/CS membrane had an ideal pure water flux (PWF) of 1470 (L·m−2·h−1) and the separation efficiency of 99.7 % for anionic dye and 99.4 % for oil–water emulsion. The contaminant on the membrane surface can be quickly removed by washing with DI water. The overall performance of the membrane is also maintained at a very high level of long-term filtration of wastewater. In summary, this study provides a new approach to complex wastewater treatment technology.

Enhancing wettability and adhesive properties of PVDF-based substrates through non-thermal helium plasma surface modification

Polyvinylidene fluoride (PVDF) has gained attention as a promising material for tissue engineering due to its biocompatibility and piezoelectricity. However, achieving proper cell adhesion to PVDF surfaces remains a challenge. This study focuses on the preparation and characterization of PVDF-based substrates, including PVDF thin films and nanocomposites incorporating CoFe2O4 magnetic nanoparticles. Helium plasma treatment is employed to modify the surface properties of these substrates. The plasma treatment induces significant changes in the topography of the PVDF-based nanocomposites. The roughness values of the samples increase from 2–3 nm to 14–17 nm after 90 s of plasma treatment, leading to enhanced hydrophilicity with an average contact angle below 60°. Importantly, the helium plasma treatment preserves the magnetic and structural properties of the substrates, suggesting the retention of their magnetoelectric properties and, thus treated composites hold potential for remote stem cell activation. We provide evidence of cytocompatibility and improved adhesive properties of plasma-treated substrates using human mesenchymal stem cell cultures.

Printed Capacitive Immunoassay for Detecting SARS-CoV-2 Viral Particles

The key to fight against a global pandemic such as COVID-19 is to have low-cost, reliable and fast response diagnostic tools. Electronic biosensors are preferred because of their ease of integration into current centralized health care networks and integration with modern point-of-care testing (POCT) devices. Printed electronic sensors provide a sensitive and reliable diagnostic platform to aid in controlling transmissible diseases. In this work, we demonstrate a fully printed capacitive biosensor. The sensor uses coplanar electrodes, coupled with capture antibodies immobilized on microporous Polyvinylidene-fluoride (PVDF) film to detect the SARS-CoV-2 spike protein in spiked buffer solutions. Antibody immobilization on PVDF surface is confirmed with confocal fluorescent imaging microscopy. Gold nanoparticle (GNP) tagged detection antibodies are also introduced to provide increased sensitivity. The gold nanoparticles provide a reflectance layer which leads to increased capacitance. This increased capacitance can be measured directly and has demonstrated the ability to screen for spiked samples with statistical significance. This fully printed capacitive immunoassay has the potential to be used as a transmissible disease screening and vaccine efficacy assessment tool for resource-limited areas.

Photoelectrocatalytic modification of nanofiltration membranes with SrF2/Ti3C2Tx to simultaneously enhance heavy metal ions rejection and permeability

Heavy metal pollution can significantly harm water systems and human health. Combining photoelectrocatalytic (PEC) and nanofiltration (NF) membrane separation technologies can effectively remove heavy metal ions from wastewater. In this study, a water bath method was used to form SrF2/Ti3C2Tx (ST) nanoparticles on the surface of polyvinylidene fluoride (PVDF) membranes and an additional polyamide (PA) functional layer was formed at the interface by crosslinking. ST@PA composite NF membranes (STPP) with good photocatalytic performance were obtained. The separation and catalytic properties of the STPP membranes were controlled by the ST content, which modifies the surface structure and properties of the membranes. The membrane with optimal ST crosslinking exhibited a water contact angle of 50.8°, pure water flux of 24.6 L·m−2·h−1·bar−1, and rejection rates of Mn2+, Ni2+, Cu2+, and Zn2+ of 98.8%, 95.3%, 95.7%, and 97.3%, respectively, under PEC-assisted separation with visible light illumination from a Xe lamp (300 W) and an applied voltage (2 V). The STPP membranes showed improved rejection rates of heavy metal ions under PEC-assisted operation. The mechanism for the improved membrane performance under PEC conditions was preliminarily clarified considering the relationship between the photocatalytic and filtration properties of STPP membranes along with the influence of light irradiation and an external voltage on the heavy metal ions. The generation of electrons, holes, superoxide radicals, and hydroxyl radicals during membrane operation enhances the rejection rates of heavy metal ions. Based on these results, STPP membranes are considered a promising technology for industrial applications in heavy metal removal.

Synergistic Enhancement of Photocatalytic CO2 Reduction by Built-in Electric Field/Piezoelectric Effect and Surface Plasmon Resonance via PVDF/CdS/Ag Heterostructure.

Photocatalytic reduction of CO2 using solar energy is an effective means to achieve carbon neutrality. However, the photocatalytic efficiency still requires improvements. In this study, polyvinylidene fluoride (PVDF) ferroelectric/piezoelectric nanofiber membranes are prepared by electrospinning. Cadmium sulfide (CdS) nanosheets are assembled in situ on the surface of PVDF based on coordination between F- and Cd2+ , and then Ag nanoparticles are deposited on CdS. Because of the synergistic effect between localized surface plasmon resonance of Ag nanoparticles and the built-in electric field of PVDF, the CO2 photocatalytic reduction efficiency using PVDF/CdS/Ag under visible light irradiation is significantly higher than that of any combination of CdS, CdS/Ag, or PVDF/CdS. Under micro-vibration to simulate air flow, the CO2 reduction efficiency of PVDF/CdS/Ag is three times higher than that under static conditions, reaching 240.4µmol g-1 h-1 . The piezoelectric effect caused by micro-vibrations helps prevent the built-in electric field from becoming saturated with carriers and provides a continuous driving force for carrier separation.

Surface modification of PVDF hollow fiber ultrafiltration membranes for biopharmaceutical products, virus, and bacterial phage removal technology

In this study, radicals were chemically formed at the hydroxyl (-OH) sites on the surface of polyvinylidene fluoride (PVDF) hollow fiber membranes, and anionic-hydrophilic and hydrophobic materials were grafted onto the surface through -OH radical reaction to generate anions (−28, −41 mV). These membranes were then used as biomembranes (BMs) and showed excellent properties. We also studied the effects of chemical surface modification and reduction in pore size (60–130 nm) according to molecular weight. After anionic modification, the electrostatic repulsion between the pore surface and the bacteria prevents adsorption when anionic bacteria pass through the pores. Particles do not pass through the asymmetric pores due to agglomeration, resulting in separation. The hydrophilic membrane had a high initial water flux, but the flux gradually decreased due to fouling. In contrast, the hydrophobic modified membrane had a low initial water flux that eventually stabilized due to excellent fouling resistance. The protein recovery ratio (PRR) was 98.8 % for hydrophilic particles and 99.2 % for hydrophobic molecules, showing a higher PRR than the pristine membrane (96.4 %). An evaluation of removal of the gram-negative bacteria Brevundimonas diminuta (Bd) showed that no bacteria in membrane-purified solutions, confirming 100 % removal efficiencies. The developed membrane can be used in biopharmaceutical production and removal of proteins, retro viruses, and bacteria.

Super hydrophilic Sodium Alginate Coating on the Surface of Polyvinylidene Fluoride via Freezing and Salting-out for Achieving Emulsion Oil Purification

In recent, oily wastewater as a special contaminant has seriously impacted the ecological environment. In this work, nature and green materials are used to prepare the SA-PVDF membrane taking freezing and salt out super hydrophilic modifying. Therefore, obtained membrane exhibited good membrane flux, excellent recyclability, and superior separation efficiency. More importantly, obtained filter membrane was green, eco-friendly, and cost-affordable. Therefore, such a simple, universal, and facile method could be used in other organic and inorganic materials for preparing filter membranes, which plays a significant role in construing novel filtration membranes to remove oil from oily wastewater in practical life.

Conductivity-Controlled Polyvinylidene Fluoride Nanofiber Stack for Absorption-Dominant Electromagnetic Interference Shielding Materials.

This work presents a novel method for achieving lightweight electromagnetic interference (EMI) shielding materials with high EMI shielding effectiveness (SE) through absorption-dominant mechanisms, utilizing only organic polymer nanofibers (NFs). Instead of incorporating high-density fillers, the approach involves adjusting the concentrations of iron chloride in the NFs and subsequent vapor phase polymerization (VPP) to control the polymerization density of poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of polyvinylidene fluoride (PVDF) NFs. This process results in NF layers with varying conductivity, creating a conductivity gradient structure. The conductivity gradient structure of the NF layers significantly enhances absorptivity by reducing impedance mismatches between the shielding material and the surrounding air, as well as between different interlayers. This reduction in impedance mismatches allows for efficient dissipation of absorbed electromagnetic (EM) waves within the highly conductive NF layer. This improved absorptivity is also attributed to the attenuation of EM wave energy through multiple reflections and scattering within the NF pores. Moreover, the gradient structure of the NF layers promotes interfacial polarization, further contributing to the effective absorption of electromagnetic waves. As a result, a high absolute EMI SE (SSEt) of 12,390 dB·cm2 g-1 with low reflectivity (0.32) was achieved without compromising the lightweight and flexible properties.

Piezoelectric field enhanced photocatalytic efficiency of PVDF/TiO2 core/shell nanofibrous membrane via coaxial electrospinning

Polyvinylidene fluoride (PVDF)/titanium dioxide (TiO2) core/shell composite nanofibrous membranes (CNMs) with large surface area and abundant reactive sites were prepared via coaxial electrospinning, showing an excellent photocatalytic degradation of phenol in a liquid phase. Coaxial electrospinning has been chosen as a versatile and one-step approach in the preparation of this active media, where TiO2 nanoparticles (NPs) are immobilized on the surface of PVDF, which exhibits piezoelectric properties if properly stimulated. Indeed, the air flow in the reactor enhanced the photocatalytic activity of PVDF/TiO2 CNM under UV irradiation, which was less evident for polyacrylonitrile/TiO2 CNM, TiO2 NPs, and neat PVDF membrane, owing to the piezo-potential field generated on the PVDF core-fibers. ∙OH and h+ were the main active species, while O2−∙ and e− played a relatively weak role, in the photo-oxidation of the tested organic compound. This flexible and recoverable PVDF/TiO2 membrane has shown to be a good candidate for promoting advanced piezo-photocatalytic properties and its practical applications for wastewater treatment.

A simple surface modification method to prepare versatile PVDF electrospun nanofibrous felts for separation, sterilization and degradation

The discharge of oily effluents from industrial production and crude oil spills at sea result in significant water pollution, posing a major danger to the environment and human health. Due to the tiny droplet size, emulsion separation is a difficult task in the separation and purification of oily wastewater. Polydopamine (PDA) and TiO2 nanoparticles were coated on the surface of polyvinylidene fluoride (PVDF) electrospun nanofibrous to increase surface roughness, and then the low surface energy substance octadecylamine (ODA) was grafted. As a result, a superhydrophobic PVDF@PDA/TiO2@ODA nanofibrous felts with a water contact angle of 168.1° has been developed. Because of their three-dimensional porous structure, the nanofibrous felts have a porosity of up to 72.9 %. The tensile strength of a series of reinforced PVDF@PDA/TiO2@ODA nanofibrous felts reaches 30.06 MPa, which is useful for maintaining the stability of the nanofibrous felts during the pressure separation. The oil and water in the emulsion are entirely separated due to the selective permeability induced by the strong superhydrophobic and superlipophilic properties. The separation efficiency of over 99 % and flow flux of above 1100 L·m−2·h−1 are achieved. The performance of the nanofibrous felts in inhibiting bacterial growth was then investigated, and it is found that a significant inhibition circle appeared in the flat dish diffusion method, with a bacteriostasis rate exceeding 99 %. This result demonstrates that PVDF@PDA/TiO2@ODA nanofibrous felts have excellent antimicrobial properties. Finally, UV–vis absorption spectroscopy was employed to demonstrate the good catalytic degradation of organic dyes by PVDF@PDA/TiO2@ODA nanofibrous felts. PVDF@PDA/TiO2@ODA nanofibrous felts have a variety of applications in the deep separation and purification of oily wastewater due to these characteristics.

Ag@BiOBr/PVDF photocatalytic membrane for remarkable BSA anti-fouling performance and insight of mechanism

Membrane technologies offer great potential in desalination and wastewater treatment. However, the serious issue of membrane fouling results in the unsatisfactory sustainability and reusability for treating wastewater containing high level of organic foulants. In this work, a photocatalytic membrane reactor system combining Ag@BiOBr photocatalyst and polyvinylidene fluoride (PVDF) ultrafiltration with remarkable anti-fouling property was constructed. The integrated Ag@BiOBr/PVDF photocatalytic ultrafiltration membranes were prepared by blending Ag@BiOBr nanoparticles (NPs) into PVDF membrane via phase inversion method. The membrane separation performance and fouling resistance were studied in a cross-flow ultrafiltration system using bovine serum albumin (BSA) as the model foulants. Compared with the pristine PVDF membrane, the hydrophilicity and surface smoothness of composite membranes were promoted by photocatalyst-incorporation, the Ag@BiOBr/PVDF membrane with the optimal Ag@BiOBr blending content of 2.0 wt% achieved both enhanced water flux and higher BSA rejection efficiency. More importantly, the mechanism of anti-fouling and self-cleaning performances were further studied, the photocatalysis process based on Ag@BiOBr/PVDF membrane effectively decomposed the BSA foulant into broken protein with induced change of carbonyl, ionic bond and hydrogen bond contents in BSA foulants via the active radicals, weakened the intermolecular force of BSA foulants to prevent membrane pore blockage. Meanwhile, the broken protein peptide chains with more negative charges could result in the strength of electrostatic repulsive forces between BSA molecules and membrane. As a result, the BSA foulant could be stably removed in the Ag@BiOBr/PVDF photocatalytic ultrafiltration system under visible light irradiation, achieving the excellent anti-fouling performance by preventing the membrane pore blockage and foulant adhesion. We believe the Ag@BiOBr/PVDF photocatalytic membrane presented in this study will be one example among many photocatalyst-membrane combinations that can be further pursued for organic pollutants removal. In particular, we expect the theoretical support can present a great opportunity to design novel photocatalytic membranes with sustainable anti-fouling performance.

NMP-induced surface self-corrosion-assisted rapid spin-coating method for synthesizing imprinted heterojunction photocatalyst anchored membrane towards high-efficiency selective degradation tetracycline

The membrane immobilization of imprinted photocatalysts is a good cooperative model, which not only gives self-cleaning and selectivity to the membrane but also solves the problem of difficult recycling and reuse of powder catalysts. Nevertheless, the problem of catalyst encapsulation and pore blockage limits its practical application. Herein, 1-methyl-2-pyrrolidone (NMP)-induced surface self-corrosion-assisted rapid spin-coating method was first proposed to prepare imprinted perylene diimide/poly-3,4-ethylenedioxythiophene heterojunction photocatalyst anchored membrane (I-PDI/PEDOT-M) with high stability and permeability. NMP can corrode polyvinylidene fluoride (PVDF) membrane and cause pore wall collapse on PVDF surface. The collapse of the pore wall firmly anchored the imprinted PDI/PEDOT heterojunction photocatalyst (I-PDI/PEDOT) into the surface pore of the PVDF membrane, effectively enhancing the stability. More importantly, this method did not produce a dense layer of traditional spin-coating solution, and I-PDI/PEDOT was fully exposed in the surface pores of the membrane to contact pollutants, thus maintaining high water flux and photodegradation activity. Besides, the construction of heterojunction structure and the introduction of imprinted cavities resulted in the good self-cleaning performance, excellent photocatalytic performance and significant specific degradation ability of I-PDI/PEDOT-M. The degradation activity of tetracycline (TC) with I-PDI/PEDOT-M was 11.05 times that of ciprofloxacin, and the selectivity coefficients of I-PDI/PEDOT-M were 2.51and 1.63 relative to PDI-M and non-imprinted PDI/PEDOT heterojunction photocatalyst, respectively. Additionally, the theoretical calculation and toxicity experiment proved that the toxicity was significantly reduced after degrading TC by I-PDI/PEDOT-M. This work provides an interesting idea for the design of highly stable and permeable photocatalytic membrane and highly selective degradation of specific pollutant.

Surface Zwitterionization via Grafting of Epoxylated Sulfobetaine Copolymers onto PVDF Membranes for Improved Permeability and Biofouling Mitigation

Grafting of zwitterionic moieties has been shown to overcome the decrease in permeability after membrane modification. Herein, we report the grafting of epoxylated sulfobetaine (poly(glycidyl methacrylate-co-sulfobetaine methacrylate or poly(GMA-co-SBMA)) zwitterionic copolymers onto polyvinylidene fluoride (PVDF) surfaces to obtain superhydrophilic and superoleophobic membranes. The three-dimensionally modified membranes simultaneously exhibit excellent fouling resistance and hemocompatibility with improved water permeability during protein filtration. The zwitterionic moiety in the bulk membrane promotes the formation of a hydration layer, resulting in a dramatic reduction in hydrophobic interactions between the membrane and proteins or bacteria. Zwitterionic polymers establish a relatively electrically neutral surface through the presence of positive and negative charge groups on their pendant, leading to a reduction of adhesion between charged protein molecules and membranes. The modified PVDF surface exhibits very high hemocompatibility for human erythrocytes, platelets, and leukocytes. In the static fouling test, this biofouling hardly adhered to the membrane surface. The developed membrane has 3 times higher water permeability than the unmodified commercial membrane. It also showed a significant improvement in antifouling performance during dynamic fouling testing. Furthermore, flux regeneration of the modified membranes is easier to achieve by simple water recirculation compared to pristine PVDF membranes. Therefore, this study provides a promising way to develop antifouling membrane surface modification, which can be potentially used for bioseparation applications.

Influence of clinical hemodialysis membrane morphology and chemistry on protein adsorption and inflammatory biomarkers released: In-situ synchrotron imaging, clinical and computational studies

Hemodialysis (HD) is often accompanied with activation of biochemical cascade reactions, caused by undesirable protein adsorption, which results in severe consequences for HD patients. Present research aims to study three hemodialysis membranes currently available in the Canadian hospitals of polyacrylonitrile (PAN), polyethersulfone (PES) and polyvinylidene fluoride (PVDF) and their interaction with three main human serum proteins: Human Serum Ablumin (HSA), Human Serum Fibrinogen (FB) and Human Serum Transferrin (TRF). In-situ synchrotron-based X-ray tomography (SR-μCT) was used to evaluate main membranes characteristics such as fiber diameter, pore size and their distribution, as well as to study the process of protein adsorption on the membranes surface and along membrane matrices. Scanning Electron Microscopy (SEM) was also used to investigate the morphology of proteins deposited on the membrane surface. Furthermore, interaction of membranes with inflammatory biomarkers was studied. Collected blood samples from HD patients were analyzed using Luminex assay for the inflammatory biomarkers of Serpin/Antitrombin-III, Properdin, C5a, 1L-1α, 1L-1β, IL-6 and TNF-α. Our results indicate the difference in the interaction of membranes with proteins is mainly attributed to a membrane surface charge and membrane chemistry. PAN and PES membranes, which are possessing high negative charge (-41.5mV and -68mV) and polar surface groups, would alter the morphology of adsorbed HAS and FB, while PVDF surface does not affect protein crystals growth. Furthermore, the molecular docking results showed that the highest interaction energy of human serum proteins was with PES membrane. The increased interaction of PES membrane with human serum proteins has triggered inflammation reactions. The release of C5a, IL-6 and Serpin cytokines for PES membrane was drastically higher compared to PAN and PVDF. The relative increase in those cytokine concentrations was 400-2000% for PES membrane, while it decreased by 10-40% for PAN and PVDF. It is worth noted that PVDF membrane had the lowest charge of -2.5 mV among investigated membranes, and it possessed the lowest interaction with human serum proteins and the least inflammation response.

Enhanced bone regeneration via ZIF-8 decorated hierarchical polyvinylidene fluoride piezoelectric foam nanogenerator: Coupling of bioelectricity, angiogenesis, and osteogenesis

Piezoelectric biomaterials are advantageous in terms of easy generation of transduced bioelectrical signals to skeleton systems in response to body movements or external stimulations. In the bone formation process, the coupling of angiogenesis-osteogenesis is crucial but the effect of piezoelectric biomaterials on angiogenesis and mechanism of stress-transformed electrical signals affecting vascular cells remain elusive. In this work, hierarchically architected polyvinylidene fluoride (PVDF) foam fabricated by solid-state shearing milling was further decorated with ZIF-8 nanocrystals. The unique hierarchical porous structure realizes stable voltage outputs up to 10 V without polarization. The electric potential of piezoelectric PVDF affected molecular trajectory of Zn2+ released from ZIF-8, leading to Zn2+ enrichment around the PVDF surface. Under piezoelectric condition, PVDF/ZIF-8 foams promoted in-vitro angiogenic and osteogenic activity as well as antibacterial effect. Upon calvarium and femur defect repair, PVDF/ZIF-8 piezoelectric foams also guided vascularized bone regeneration through micro-current stimulation and Zn2+ enrichment. RNA-seq demonstrated PVDF/ZIF-8 piezoelectric foam mainly up-regulated ATP coupled cation transmembrane transportation in vascular endothelial cells, which enhanced cellular uptake of Zn2+, indicating the synergistic effect of piezoelectric PVDF and bioactive ZIF-8. This work offers a preliminary explanation for mechanism of angiogenesis-osteogenesis coupling of PVDF/ZIF-8 foam nanogenerator and provides a valuable complement to clinical treatment strategies for bone defect repair.

Atomistic-Scale Energetic Heterogeneity on a Membrane Surface.

Knowing the energetic topology of a surface is important, especially with regard to membrane fouling. In this study, molecular computations were carried out to determine the energetic topology of a polyvinylidene fluoride (PVDF) membrane with different surface wettability and three representative probe molecules (namely argon, carbon dioxide and water) of different sizes and natures. Among the probe molecules, water has the strongest interaction with the PVDF surface, followed by carbon dioxide and then argon. Argon, which only has van der Waals interactions with PVDF, is a good probing molecule to identify crevices and the molecular profile of a surface. Carbon dioxide, which is the largest probing molecule and does not have dipole moment, exhibits similar van der Waals and electrostatic interactions. As for water, the dominant attractive interactions are electrostatics with fluorine atoms of the intrinsically hydrophobic PVDF membrane, but the electrostatic interactions are much stronger for the hydroxyl and carboxyl groups on the hydrophilic PVDF due to strong dipole moment. PVDF only becomes hydrophilic when the interaction energy is approximately doubled when grafted with hydroxyl and carboxyl groups. The energetic heterogeneity and the effect of different probe molecules revealed here are expected to be valuable in guiding membrane modifications to mitigate fouling.

Surface functionalization of ion-in-conjugation polymer sensors for humidity-independent gas detection at room temperature

Organic semiconductors rising as promising chemiresistive materials due to their high sensitivity and high selectivity towards target gas molecules. However, severe interference from moisture remains unsolved despite years of materials innovation. Herein, we realized humidity-independent detection of NO2 as low as 40 parts-per-billion (ppb) at varied humidity up to 80 % RH and room temperature (RT) through functionalization of the organic semiconductor film by polyvinylidene fluoride (PVDF) fibers. This strategy of PVDF surface functionalization is not only universally applicable to different gas sensing materials. The hydrophobic PVDF fibers repel water vapor but allow NO2 diffusing onto the beneath sensing layer, achieving a time stability up to five months at 80 % RH. The sensor devices are endowed with good flexibility (bended to 90° for 5000 times) by sticking the rigid organic semiconductor particles from cracking by the fibers during device bending. Our method is hopefully applicable to a wider range of organic semiconductors, prompting more organic gas sensors with excellent humidity-resistant performance.

Rapid Forming of Nanowire Array on Polyvinylidene Fluoride Polymer Surfaces at Room Temperature by Ultrasonic Loading

Forming nanostructures on a substrate have been an effective approach to regulating surface properties without changing material chemical compositions. However, such nano‐forming processes are generally based on thermal plastic forming that needs to heat substrate material to its melting point, which is time‐consuming and induces a risk of oxidation, aging, or phase transition, especially when the material is a polymer. This research work develops a novel method to rapidly form nanowire arrays on polyvinylidene fluoride (PVDF) polymer at room temperature. Assisted by ultrasonic vibration, nanowires with a diameter of 200 nm are formed on PVDF surface within 0.7 s, while the highest forming temperature is 124 °C only, which is much lower than the melting point. In addition, the original β phase of PVDF can be retained after nano‐forming by adjusting ultrasonic loading time. The agglomeration mechanism of the formed nanowires on the surface was also proposed based on the transverse flow and residual stress release during ultrasonic forming process. The water contact angle measurement showed that nanowire arrays altered the surface wettability of PVDF from hydrophilic to hydrophobic. This ultrasonic‐assisted processing provides a new approach for functional surface design of PVDF and rapid nanostructure forming for various applications.