Polyvinylidene Fluoride Nanofibrous Membranes Research Articles

Directional vapor transported and water-proof nanofibrous membranes for liquid desiccant dehumidification systems

The membrane-based liquid desiccant dehumidification system is a newly developed method in the field of air dehumidification. In this study, double-layer nanofibrous membranes (DLNMs) with directional vapor transport and water repellency for liquid dehumidification were fabricated by a simple electrospinning process. Specifically, the combination of thermoplastic polyurethane nanofibrous membrane and polyvinylidene fluoride (PVDF) nanofibrous membrane forms a cone-like structure in DLNMs, resulting in directional vapor transportation. The nanoporous structure and rough surface of PVDF nanofibrous membrane provide waterproof performance for DLNMs. Compare with the commercial membranes, the proposed DLNMs have a significantly higher water vapor permeability coefficient, which is as high as 539.67 g·μm m−2·24 h·Pa. This study not only provides a new route to construct a directional vapor transport and waterproof membrane, but also demonstrates the huge application prospect of the nanofibrous membrane formed by electrospinning in the field of solution dehumidification.

Superhydrophilic PVDF nanofibrous membranes with hierarchical structure based on solution blow spinning for oil-water separation

Nanofibrous membranes (NFMs) are frequently used in oil-water separation thanks to their high porosity, controllable pore size, and convenience in modification to obtain super wettability. However, the low production rate and dense structure of NFMs have limited the industrial applications. In this work, zinc oxide (ZnO) seed loaded polyvinylidene fluoride (PVDF) NFMs with fluffy structure were prepared through solution blow spinning (SBS). Subsequently, ZnO nanowires (NWs) were synthesized based on the seeds through ultrasonic assisted hydrothermal reaction, constructing superhydrophilic surface with hierarchical structure. The u-ZnO-NWs/PVDF showed uniform morphology throughout the entire membrane with an average fiber diameter of 517.35 ± 158.72 nm and an average nanowire diameter of 72.55 ± 20.52 nm, which resulted in a low average pore size (4024.68 ± 393.40 nm), superhydrophilicity, and underwater oleophobicity. The nanowire equipped membrane revealed super high water flux (12960.77 ± 325.04 L·m−2·h−1·bar−1), which could be applied in the separation of oil-in-water emulsions with high separation efficiency (>97 %) and high flux (about 8000 L·m−2·h−1·bar−1) under gravity. Results indicated the potential of SBS u-ZnO-NWs/PVDF in the fields of oil-water separation, sewage treatment, as well as catalytic degradation.

Electrospun PVDF Nanofibers for Piezoelectric Applications: A Review of the Influence of Electrospinning Parameters on the β Phase and Crystallinity Enhancement.

Polyvinylidene fluoride (PVDF) is among the most attractive piezo-polymers due to its excellent piezoelectricity, lightweight, flexibility, high thermal stability, and chemical resistance. PVDF can exist under different forms of films, membranes, and (nano)fibers, and its piezoelectric property related to its β phase content makes it interesting for energy harvesters and wearable applications. Research investigation shows that PVDF in the form of nanofibers prepared by electrospinning has more flexibility and better air permeability, which make them more suitable for these types of applications. Electrospinning is an efficient technique that produces PVDF nanofibers with a high β phase fraction and crystallinity by aligning molecular dipoles (–CH2 and –CF2) along an applied voltage direction. Different nanofibers production techniques and more precisely the electrospinning method for producing PVDF nanofibers with optimal electrospinning parameters are the key focuses of this paper. This review article highlights recent studies to summarize the influence of electrospinning parameters such as process (voltage, distance, flow rate, and collector), solution (Mw, concentration, and solvent), and ambient (humidity and temperature) parameters to enhance the piezoelectric properties of PVDF nanofibers. In addition, recent development regarding the effect of adding nanoparticles in the structure of nanofibers on the improvement of the β phase is reviewed. Finally, different methods of measuring piezoelectric properties of PVDF nanofibrous membrane are discussed.

Fabrication of superhydrophobic PDTS-ZnO-PVDF membrane and its anti-wetting analysis in direct contact membrane distillation (DCMD) applications

Membrane distillation (MD) is an emerging water treatment technology suitable for hypersaline wastewater. However, membrane wetting is a primary obstacle to restrict its widespread industrial use. In this study, a superhydrophobic nanofibrous membrane (labeled as FZP) with high water contact angle of 162.3° and sliding angle of 9.8° was fabricated through fluorinating of zinc oxide (ZnO) blended electrospun polyvinylidene fluoride (PVDF) membrane. In comparison with neat and ZnO blended PVDF (ZP) nanofibrous membranes, FZP membrane has much better anti-wetting property due to its superhydrophobicity and higher liquid entry pressure (LEP) value when desalinating both pure NaCl solution and NaCl solutions with low-surface-tension sodium dodecyl sulfate (SDS) and sparingly soluble salt CaSO4. LEP values of membranes for SDS and CaSO4 contained feed solutions were calculated to be smaller than that for pure NaCl solution, accelerating the occurrence of membrane wetting. Temperature gradient across the membrane and Gibbs free energies of CaSO4 heterogeneous nucleation were further calculated to elucidate the wetting mechanism. Our results provide valuable insights for better developing superhydrophobic membrane and understanding its anti-wetting property in MD process.

Perflurooctyltriethoxy silane and carbon nanotubes-modified PVDF superoleophilic nanofibre membrane for oil-in-water adsorption and recovery

Due to the increased rate of oil spills leading to environmental water pollution, the synthesis of nanofibre membranes with controlled superhydrophobic/superoleophilic properties has received remarkable attention for oil-water separation. In this research, superhydrophobic-superoleophilic nanofibre membranes were successfully prepared through a three-step deposition of perflurooctyltriethoxy silane (POTS) to carbon nanotubes (CNTs) followed by dispersing the mixture in polyvinylidene fluoride (PVDF) polymer solution prior to electrospinning. Upon the addition of POTS/CNTs on the nanofibre membranes, the hydrophobicity increased from 96.35° to 143.30°, thus, resulting in improved oil adsorption capacity from 60.20 to 111.4 g·g-1. The intraparticle diffusion model provided the information on external mass transfer and diffusion of the oil from the oleophilic sites of the adsorption active sites. The CNTs/POTS-modified PVDF nanofibre membranes demonstrated high adsorption efficiencies ∼ 99% towards avocado, sunflower, engine, and motor oils. Based on Chi-square test statistics, the adsorption of oils on CNTs/POTS-modified PVDF nanofibre membranes followed the first-order kinetics. The rate constants increased from 0.019 to 0.034 g·g-1 min-1 upon the incorporation of CNTs/POTS on PVDF nanofibre membranes; thus, indicating the improvement of adsorption of oils. Remarkably, PVDF-based nanofibre membranes were recycled and reused for more than 37 cycles, confirming their potential application for environmental oil-water separation.

Omniphobic PVDF nanofibrous membrane for superior anti-wetting performance in direct contact membrane distillation

Membrane wetting caused by low surface tension pollutants in feed solution has been a major challenge for membrane distillation (MD), and omniphobic membranes have been proposed as a promising solution to address this challenge due to their strong repellence towards liquids with a broad range of surface tensions. In this study, we report a nanoparticle-free strategy to fabricate omniphobic polyvinylidene fluoride (PVDF) nanofibrous membranes for robust MD desalination. A solvent-thermal induced roughening method was used to create multiscale hierarchical nanofin structures on electrospun PVDF nanofibers, followed by a polydopamine-anchored surface fluorination treatment to reduce the surface energy of the nanofibrous membrane. We show that the as-prepared membrane exhibited super repellence (>150°) to diverse liquids with surface tension ranging from 73 to 30 mN m−1. Moreover, the omniphobic membrane maintained stable salt rejection and water flux in direct contact MD processes in the presence of sodium dodecyl sulfate surfactant (up to 0.4 mM) or mineral oil (up to 480 mg L−1), demonstrating its promising potential in practical water reclamation from MD applications.

Mechanically stretchable piezoelectric polyvinylidene fluoride (PVDF)/Boron nitride nanosheets (BNNSs) polymer nanocomposites

Mechanically stretchable piezoelectric materials are required by wearable devices, such as self-powering sensors and energy harvesters that can monitor human movement and vital biosignals. Polyvinylidene fluoride (PVDF) is a common choice for making flexible piezoelectric sensors but has limited stretchability (strain to failure). Herein we present a new method of significantly increasing the strain-to-failure of PVDF nanofibre membranes by incorporating amino-functionalised boron nitride nanosheets (BNNSs). The PVDF-BNNS nanocomposites were prepared by firstly dispersing a small amount of BNNSs, less than 1.5 wt%, into a PVDF solution and electrospinning. Compared to the un-modified PVDF, the addition of BNNSs yielded increases of eleven times, twice, and forty times in strength, stretchability, and in-plane thermal conductivity, while piezoelectric performance remains unaffected. The higher thermal conductivity offers significantly better heat dissipation ability of piezoelectric sensors than the un-modified PVDF material.

Enhanced flux in direct contact membrane distillation using superhydrophobic PVDF nanofibre membranes embedded with organically modified SiO2 nanoparticles

AbstractBACKGOUNDMembrane distillation (MD) is a promising low‐cost and efficient desalination process, yet it has not been fully implemented at an industrial scale. Membrane wetting and low porosity are limiting factors leading to low water recovery rates. The current study involved the synthesis of membranes that combined high mechanical stability, porosity and superhydrophobicity, to prevent wetting, with high salt rejection and water flux.RESULTSSilica nanoparticles (SiO2NPs) were synthesized by a novel green chemistry procedure, modified with three different silane reagents [octadecyltrimethoxysilane, N‐octadecyltrichlorosilane (ODTS) and chlorodimethyl‐octadecyl silane] and finally embedded on polyvinylidene fluoride (PVDF) nanofibre membranes using an in‐situ electrospinning technique. These modified membranes displayed a Young's modulus of ∼43 MPa and showed highly porous properties (∼80% porosity, 1.24–1.41 μm pore sizes) and superhydrophobic surfaces (contact angle >150o); thus possessing parameters falling within the range of highly recommended values in MD. Remarkably, the concentration of modified SiO2NPs used to produce the superhydrophobic PVDF nanofibre membranes was significantly lower (1% w/w) than those reported in the literature (3–4% w/w), clearly indicating the efficiency of these silane reagents.CONCLUSIONMembranes embedded with ODTS‐modified SiO2NPs were the most efficient; rejecting salts at high efficiencies (>99.9%) with water fluxes of ≈34.2 LMH at 60 °C, thus indicating their capacity as an energy‐efficient process to produce high purity water. © 2019 Society of Chemical Industry

One-step tailoring surface roughness and surface chemistry to prepare superhydrophobic polyvinylidene fluoride (PVDF) membranes for enhanced membrane distillation performances

Superhydrophobic polyvinylidene fluoride (PVDF) membrane is a promising material for membrane distillation. Existing approaches for preparing superhydrophobic PVDF membrane often involve separate manipulation of surface roughness and surface chemistry. Here we report a one-step approach to simultaneously manipulate both the surface roughness and surface chemistry of PVDF nanofibrous membranes for enhanced direct-contact membrane distillation (DCMD) performances. The manipulation was realized in a unique solvent-thermal treatment process, during which a treatment solution containing alcohols was involved. We demonstrate that by using different chain-length alcohols in the treatment solvent, surface roughness can be promoted by creating nanofin structures on the PVDF nanofibers using an alcohol which has moderate affinity with PVDF. Meanwhile, surface chemistry can be tuned by adjusting the fraction distribution of crystal phases (nonpolar α phase and polar β phase) in the membrane using different alcohols. PVDF membranes with different surface wettabilities were used to evaluate the effects of surface roughness and surface energy on the DCMD performances. Combining both low surface energy and multi-scale surface roughness, pentanol-treated PVDF membrane achieved best anti-water property (water contact angle of 164.1° and sliding angle of 8.1°), and exhibited superior water flux and enhanced anti-wetting ability to low-surface-tension feed in the DCMD application.

Superhydrophobic PVDF nanofibre membranes coated with an organic fouling resistant hydrophilic active layer for direct-contact membrane distillation

Although Membrane Distillation (MD) is envisaged as a promising technology for achieving a cost-effective and sustainable recovery of water from saline solutions, membrane fouling and wetting remain the major challenges that compromise its separation efficiency. To mitigate the high fouling propensities of hydrophobic MD membranes while retaining their high salt rejection efficiencies, superhydrophobic poly-vinylidene fluoride (PVDF) nanofibre membranes embedded with silanized silica nanoparticles (f-SiO2NPs) were synthesised and coated with a hydrophilic active layer containing silver nanoparticles and carboxylated multi-walled carbon nanotubes (AgNPs/f-MWCNTs). While the f-SiO2NPs-modified PVDF nanofibres exclusively allow the transport of water vapour, the AgNPs/f-MWCNTs active provides hydrophilic and biocidal (i.e., biofouling control) properties. The morphology, hydrophobicity, thermal and mechanical properties of the PVDF membranes were rigorously characterized. The PVDF nanofibres were investigated for their resistance to flux decline using a solution containing Bovine Serum Albumin and a real complex effluent containing thermophilic bacteria. f-SiO2NPs-modified PVDF nanofibres showed the highest flux decline (82% after 60 h) associated with BSA adsorption induced by favourable hydrophobic-hydrophobic interactions. AgNPs/f-MWCNTs coated PVDF membranes showed a significant decrease in fouling (47% flux decline) and the highest salt rejections (99.8%). Remarkably, the coating layer showed high biocidal properties towards thermophilic bacteria when subjected to effluent. The current approach provides an important step towards a successful implementation of MD processes at a pilot-scale for water desalting.

Development of highly-efficient ZIF-8@PDMS/PVDF nanofibrous composite membrane for phenol removal in aqueous-aqueous membrane extractive process

A highly-efficient zeolitic imidazolate framework-8 (ZIF-8) embedded polydimethylsiloxane (PDMS) mixed matrix membrane (MMM) supported by a polyvinylidene fluoride (PVDF) nanofibrous substrate was developed for phenol removal in an aqueous-aqueous membrane extractive process. Homogeneous nano-scaled dispersion of ZIF-8 in the PDMS matrix was achieved by direct incorporation without intermediate drying process, where the interaction of the randomly-moved nanofillers could be prevented, leading to evenly dispersed ZIF-8 nanofillers and defect-free ZIF-8@PDMS/PVDF nanofibrous composite membranes. The newly-developed ZIF-8@PDMS/PVDF membrane exhibited an exceptionally high overall mass-transfer coefficient, k0 of 35.7 ± 1.1 × 10−7 m/s, doubling that of the pristine membrane in the membrane extractive process. The high performance was maintained for over 360 h without loss of salt rejection. These results could be attributed to the organophilic-assisted “bi-mode” transporting mechanism of ZIF-8 nanofillers in PDMS matrix, namely: (1) the solution-diffusion transport mode; (2) the pore-flow transport mode, where the synergistic effects are expected to significantly improve the phenol transfer efficiency through the membranes. Overall, the results achieved in this work demonstrate promising potential of highly-efficient ZIF-8@PDMS/PVDF nanofibrous composite membranes used for aqueous-aqueous membrane extractive processes for organic-containing wastewater treatments.

Fabrication of PVDF nanofibrous hydrophobic composite membranes reinforced with fabric substrates via electrospinning for membrane distillation desalination

To improve the mechanical properties of the electrospun nanofibrous membrane, the nonwoven fabrics and spacer fabrics were employed as support substrates to fabricate polyvinylidene fluoride (PVDF) nanofibrous composite membranes. The influences of the substrate on membrane morphology, hydrophobicity, pore size and pore size distribution, porosity, mechanical strength and permeability were comprehensive evaluated. The electrospun composite membranes had a three dimension bead-fiber interconnected open structure and a rough membrane surface. The membrane surface presented a multilevel re-entrant structure and all the water contact angles were above 140°. In contrast with the pure PVDF nanofibrous membrane, the stress at break and the elastic modulus of the composite membranes increased by 4.5–16 times and 17.5–37 times, respectively. Since the spacer fabrics had less resistance to mass transfer, the membranes composited with spacer fabrics exhibited greater permeate fluxes compared with the composite membranes with the nonwoven fabrics as substrates. During the membrane distillation test, the highest permeate flux was up to 49.3kg/m2/hr at the feed temperature of 80°C. The long-time and repeat operation of membrane distillation desalination indicated the fabricated membrane with a good resistance to scaling and wetting. The results suggested the potential of the electrospun composite membrane for membrane distillation application.

Graphene quantum dots modified polyvinylidenefluride (PVDF) nanofibrous membranes with enhanced performance for air Gap membrane distillation

This study investigates the potential of novel graphene quantum dots (GQDs)/polyvinylidene fluoride (PVDF) nanofibrous membranes for water desalination via air gap membrane distillation (AGMD) process. Different contents of GQDs were loaded in/on nanofibrous membrane for obtaining the desired structure for AGMD process. The resultant GQDs/PVDF nanofibrous presented a slight decrease in water contact angle and considerable increase in liquid entry pressure of water (LEPw). The sample containing 0.25 wt.% GQDs exhibited porosity of >90%, LEPw of >135 kPa, mean average surface roughness of 189.24 nm and water contact angle of >125°. Furthermore, the BET analysis exhibited that the mean pore diameter and effective surface area of nanofibrous membrane were modified at presence of GQD. AGMD experiments indicated that the higher water flux of 17.6 kg/m2 h and salt rejection of about 99.7% were achieved for GQD3P membrane containing 0.25 wt% GQDs compared to neat PVDF nanofibrous membrane with water flux of about 14.7 kg/m2 h and salt rejection of about 94.5% (partial wetting occurred after 4 h) during filtration of 3.5 wt.% NaCl solution for 8 h under feed and permeate temperatures of 60 °C and 20 °C, respectively. Eventually, GQD3P exhibited the water flux of 10.8 kg/m2h and reliable salt rejection of >99.5% over 60 h experiment.

Polyvinyl Butyral Modified Polyvinylidene Fluoride Breathable–Waterproof Nanofibrous Membranes with Enhanced Mechanical Performance

Electrospun nanofibrous membranes with outstanding mechanical property, breathability, and waterproofness are critical in protective fields; however, great challenges still remain in creating such functional materials. A novel polyvinylidene fluoride (PVdF)/polyvinyl butyral (PVB) breathable–waterproof membrane with robust mechanical performance is fabricated by introducing thermal post‐treatment into electrospun membranes. Embedding of PVB enriches the pristine PVdF nanofibrous membranes with bonded network, optimized pore size, and porosity. The composite membranes are endowed with robust tensile stress of 10.5 MPa and good breaking elongation of 64.5%, which are about four times that of the pure non‐bonded PVdF membranes. Apart from this, the bonded PVdF/PVB membranes express integrated properties of high water vapor transmittance rate (10.6 kg m−2 d−1), modest air permeability (9.8 mm s−1), and good waterproofness (58 kPa). Furthermore, the convenience and efficient of this fabrication process will allow for large‐scale production of PVdF/PVB breathable–waterproof nanofibrous membranes with robust mechanical performance and board applications. image

Electrospinning of PVDF nanofibrous membranes with controllable crystalline phases

Effectively controlling crystalline phases of electrospun polyvinylidene fluoride (PVDF) nanofibers is crucial to produce membranes with special properties for specific applications. Here, the heating treatment during or after electrospinning has been investigated to determine an effective way to control crystalline phase of PVDF nanofibers. By simultaneously controlling the collector temperature and the flow rate during the fiber deposition, a comparatively lower temperature (≤70 °C) is required for obtaining α-, β-, or γ-phase-dominant nanofibrous membranes, whereas a much higher temperature (≥150 °C) is necessary for post-heating of already-deposited fibers. On the other hand, through finely tuning the heating during or after electrospinning, crosslinked nanofibrous membranes can be also obtained, which undoubtedly enhance mechanical performance of the membranes. Therefore, it is hopeful to fabricate high-performance electrospun PVDF nanofibrous membranes with synchronous control of crystalline phases and morphologies, which will further broaden the applications of PVDF materials.

Dual-Biomimetic Superhydrophobic Electrospun Polystyrene Nanofibrous Membranes for Membrane Distillation

A new type of dual-biomimetic hierarchically rough polystyrene (PS) superhydrophobic micro/nano-fibrous membrane was fabricated via a one-step electrospinning technique at various polymer concentrations from 15 to 30 wt %. The obtained micro/nano-fibers exhibited a nanopapillose, nanoporous, and microgrooved surface morphology that originated from mimicking the micro/nanoscale hierarchical structures of lotus leaf and silver ragwort leaf, respectively. Superhydrophobicity and high porosity of such resultant electrospun nanofibrous membranes make them attractive candidates for membrane distillation (MD) application with low energy water recovery. In this study, two kinds of optimized PS nanofibrous membranes with different thicknesses were applied for desalination via direct contact MD. The membranes maintained a high and stable permeate water vapor flux (104.8 ± 4.9 kg/m(2)·h, 20 g/L NaCl salt feed for a thinner PS nanofibrous membrane with thickness of 60 μm; 51 ± 4.5 kg/m(2)·h, 35 g/L NaCl salt feed for the thicker sample with thickness of 120 μm; ΔT = 50 °C) for a test period of 10 h without remarkable membrane pores wetting detected. These results were better than those of typical commercial polyvinylidene fluoride (PVDF) MD membranes or related PVDF nanofibrous membranes reported in literature, suggesting excellent competency of PS nanofibrous membranes for MD applications.

Preparation of a functional nanofibrous polymer membrane incorporated with poly(2-aminothio phenol) stabilized gold nanoparticles

Functional nanofibrous polymer membranes were prepared by incorporating poly(2-aminothio phenol) (P2AT) stabilized Au NPs onto electrospun polyvinylidene fluoride (PVdF) nanofibers (designated as P2AT-Au NPs@PVdF-NFM). The preparation of P2AT-Au NPs@PVdF-NFM involves two steps: loading of 2AT (monomer) into electrospun PVdF nanofibrous membrane and polymerization of 2AT by gold chloride. P2AT and Au NPs were simultaneously formed into the electrospun PVdF-NFM. Transmission electron microscope image of P2AT-Au NPs@PVdF-NFM informs the presence of Au NPs (with sizes ~10 nm) onto PVdF-NFM.

Develop Flexible Piezoelectric PVDF Nano-Fibrous Membrane

Piezoelectric polymer, polyvinylidene fluoride (PVDF) film, has been widely investigated as sensor and transducer material due to its high piezo-, pyro-, and ferroelectric properties. However, there are many limitations for PVDF film as human-related tactile sensor, such as non-breathability, stretching, requirement of additional process like poling, etc. In this paper, PVDF nano-fibrous membrane which is light, flexible, and wearable was prepared by electrospinning technique. The electrospinning parameters such as the voltage, feeding rate, tip-tocollector distance, etc, were well controlled. More than 4 hours electrospinning time was needed for a certain thickness of PVDF nano-fibrous membrane. The morphology of PVDF nanofiber was determined by scanning electron microscopy (SEM), the diameter distribution was calculated and crystal structure was evaluated by FTIR spectroscopy. We found the feasibility of developing piezoelectric PVDF fibrous membranes through electrospinning technology, which is a good candidate for flexible human-related tactile sensors to sense garment pressure, blood pressure, heartbeat rate, accidental external impact on human body, etc.

Electrospun carbon nanotubes–gold nanoparticles embedded nanowebs: prosperousmulti-functional nanomaterials

Electrospinning was employed to prepare new multi-functional nanowebs. Cyclodextrinbased inclusion complex (CD-IC) was used to disperse multiwalled carbon nanotubes(MWNT) within electrospun polyvinylidene fluoride nanofibrous membranes (PVdF-NFM).Subsequently, MWNT(CD-IC)/PVdF-NFM was loaded with gold (Au) particles. Themorphology, structure and thermal properties of Au/MWNT(CD-IC)/PVdF-NFM wereinvestigated by transmission electron microscopy, field emission scanning electronmicroscopy, FT-IR spectroscopy, x-ray diffraction spectroscopy and differentialscanning calorimetry. The new Au/MWNT(CD-IC)/PVdF-NFM is electroactiveand shows excellent electrocatalytic activity towards oxidation of ascorbic acid.