•Natural hirudin was immobilized on PLA membrane via hydrogen bonding.•The surface crosslinked PVP provided attaching spacer.•PVP/hirudin complex shows desired anti-clotting stability and activity.•The PLA membrane showed excellent dialysis capability.Different from intensively used anticoagulant heparin, hirudin as a representative of natural bio-molecular inhibitors can form specific hirudin-thrombin complex and function as a serine proteinase to efficiently prevent blood coagulation with less bleeding adverse effect, no allergic reaction and immune of non-toxic reaction. We aim to develop a novel anticoagulant polylactide (PLA) membrane via immobilizing natural hirudin through the hydrogen bonding interaction. High amount of PVP (17.4 wt%) was first immobilized on the membrane surface through the interfacial crosslinking of P(VP-VTES). The abundant carbonyl groups with high inter-association constant (K=6000) on the membrane surface dominated the hydrogen bonding interaction with the carboxyl groups of hirudin [44]. The anti-clotting activity of PLA membrane increased with the active hirudin concentration. XPS, ATR-FTIR was conducted to confirm the chemistry evolution of PLA membranes immobilized by PVP and hirudin respectively. The intermediate PVP spacer promoted the hydrophilicity and effectively inhibited the platelet adhesion. While the enhanced hemocompatibility was distinctly revealed by the blood concretion four items (APTT, PT, TT and FIB) mainly thanks to the surface immobilization of hirudin. The anti-clotting stability of PLA membrane was evaluated with varied incubation time. The complement activation was also measured in terms of C3a and C5a. The anti-clotting PLA membrane showed excellent dialysis performances in terms of cleaning urea, creatinine, lysozyme while preserving BSA respectively.

•The stereocomplex PDLA/PLLA membrane exhibits high porosity and thin skin layer.•The stereocomplex PDLA/PLLA membrane shows high water permeability and BSA rejection simultaneously.•The protein antifouling of the stereocomplex PDLA/PLLA membrane is excellent.In this work, a feasible and efficient approach was developed to produce Poly(lactic acid (PLA) ultrafiltration membrane with both high permeability and high rejection simultaneously. Poly(L-lactic acid)/Poly(D-lactic acid) (PDLA/PLLA) stereocomplex crystallites were thought to play the critical role different from the traditional pore forming agents or hydrophilic modification. The membrane morphology of the stereocomplex PDLA/PLLA membrane with high porosity and thin skin layer was observed by SEM. The addition of PDLA resulted in the thermodynamic enhancement for phase separation of PLLA casting solution as demonstrated by a rotational rheometer. The PDLA/PLLA stereocomplex crystallization behavior was investigated by DSC and XRD. With increasing the stereocomplex crystallites, the water permeability of PLA membrane significantly increased from ~482 L/m2·h to ~3325 L/m2 h, while with small loss in degree of rejection. Furthermore, the stereocomplex PLA membrane demonstrated the excellent separation efficiency for nano-TiO2 and ink dispersion. Besides, the stereocomplex PLA membrane exhibited outstanding anti-protein fouling properties through the static and dynamic BSA antifouling tests. All results demonstrated that the stereocomplexation can effectively tune the pore size evolution and control the permeability, selectivity and fouling resistance.Download high-res image (595KB)Download full-size image

To overcome the surface instability of traditional polymeric membranes especially with superwetting behaviour, a robust superhydrophilic surface was fabricated with nano-TiO2 inlaid on a hierarchical polylactide (PLA) ultrafiltration membrane via a spin coating process. Distinctly different from most previously reported nano-particle involved polymeric membranes, both the micro-/nano-architecture of the PLA membrane and the size matched nano-particle assembly constructed the robust superhydrophilic interface mimicking coral tentacle predatory behavior. The rigid surface based on the flexible polymeric membrane with the hierarchical architecture showed robust superhydrophilicity and underwater superoleophobicity even after long-term water washing treatment, which was also verified by the morphology, contact angle, XPS and adhesive force in contrast to smooth membranes. The as-prepared PLA membrane showed excellent separation performance for varieties of oil/water mixtures with a robustly high permeate flux (above 950 L m−2 h−1 under 0.1 MPa) and oil rejection (above 99%) even after 10 cycles of operation. Besides, the superhydrophilic PLA membrane exhibited outstanding anti-protein fouling properties. The PLA membrane showed relatively high BSA and ink rejection as well as water flux recovery and continuous separation stability due to rigid interface strengthening effects. The unique interface combination strategy between functional nanoparticles and polymeric membranes provided a window of opportunity for constructing robust polymeric membranes for advanced applications e.g. oil/water separation, ion exchange, in membrane catalytic reactors etc.

•The tight nanofiltration membrane possessed high rejection to concentrated salts.•The tight nanofiltration membrane with multi-charged nanofilms rejected both multivalent cations and anions.•The tight nanofiltration membrane exhibited excellent removal of heavy metal ions and dyes.The fractionation or rejection of concentrated salts by nanofiltration membrane remains the biggest challenge owning to the charge neutrality and concentration polarization. A tight nanofiltration membrane with ultrathin dually charged nanofilm down to 17±5 nm was synthesized to improve the rejection of highly concentrated salts up to 20 g/L. The ultrathin positive polyethylenimine (PEI) and negative poly(acrylic acid) (PAA) polyelectrolyte nanofilm was assembled on the loose nanofiltration membrane via the aid of bio-glue dopamine. The physicochemical property of dependent nanofilm was characterized by the surface morphology (SEM, AFM), element variation (XPS), surface charge (Zeta potential), molecular weight cut off and stokes radius respectively. The influence of dopamine deposition time and PEI concentration on separation performance was investigated. The optimum membrane exhibited outstanding rejection to diluted multivalent salts (1 g/L, 98.5% MgSO4, 98.3% Na2SO4, 97.2% MgCl2), high removal of heavy metal ions (1 g/L, 93.5% Cd2+, 95.2% Cu2+, 92.7% Pb2+) as well as high removal of dyes (100% Congo red, 99.93% Victoria blue B, 99.91% Brilliant green, 99.82% Basic red 2, 99.03% Neutral red). Moreover, the resultant membrane showed exceptional rejection to highly concentrated salts (20 g/L, 93.4% Na2SO4, 92.6% MgCl2, 93.5% MgSO4), exceeding the previously reported membranes. Both the multi-charged nanofilms and nano-scaled thickness contributed to the outstanding nanofiltration performance.Download high-res image (200KB)Download full-size image

Poly(vinylidene fluoride) (PVDF) membranes have been widely applied to treat wastewater, however, the removal of toxic aromatic phenolic compounds remains a technical challenge due to the serious adsorption fouling and difficult degradation. Herein, we aimed to design a superhydrophilic PVDF membrane decorated with Au nanoparticles, which enhanced the rapid degradation of p-nitrophenol (4-NP). The superhydrophilic PVDF membrane with a micro/nano structured surface was decorated with Au nanoparticles via poly(dopamine) (PDA) as a spacer. The influences of membrane affinity (e.g. Hydrophilic Membrane (HM), micro/nano structured superhydrophilic membrane (MSiM), and micro/nano structured superhydrophobic membrane (MSoM)) on PDA deposition and the subsequent Au decoration were comprehensively investigated. The synthesized Au nanoparticles were characterized using transmission electron microscopy (TEM) and UV-vis absorption spectra. The morphology and composition was evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static catalytic experiments demonstrated that MSiM degraded over 90% of 4-NP in 5 minutes with a kinetic reaction rate constant of 47.84 × 10−2 min−1 and high stability over 6 cycles. A membrane catalytic reactor (MCR) was designed to realize the continuous catalytic degradation of 4-NP with a kinetic reaction rate constant of 7 × 10−2 min−1.

An interesting PVDF membrane with unusual thermoresponsive behavior was prepared by the incorporation of P(OEGMA-co-VTMOS). The P(OEGMA-co-VTMOS) copolymer was first in situ synthesized in a PVDF/triethyl phosphate (TEP) casting solution. A P(OEGMA-co-VTMOS) network was assembled in the PVDF membrane through hydrolysis and condensation during phase inversion. PVDF/P(OEGMA-co-VTMOS) in organic solvent demonstrated a typical LCST around 35 °C, reflecting the reversible transition of the coil-to-globule conformation. Microphase separation was responsible for the appearance of turbidity of the casting solution. FTIR, XPS, TGA and SEM confirmed the surface enrichment of the copolymer, especially in the membrane bottom. The hydrophilicity and protein anti adsorption were improved despite the temperature variation. In particular, AFM in aqueous media was conducted to determine the reversible morphology and water channel variation under heating and cooling. Different from common thermoresponsive membranes, the so-modified PVDF membranes exhibit a reversible abnormal change of pure water flux and BSA rejection with temperature. The intriguing thermoresponsive behavior and mechanism of the modified PVDF membrane was thoroughly investigated from the aspects of PVDF/TEP casting solution, membrane morphology in aqueous media and water/BSA filtration performance.

Polylactide (PLA) has attracted much attention as a sustainable and environmentally friendly material. However, the poor heat resistance restricts its potential application as a porous membrane. Herein, a PLA membrane with excellent heat resistance, hydrophilicity and hemocompatibility was developed via a surface crosslinking induced crystallization strategy, which involved two key reactions, namely, copolymerization of N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) and the subsequent hydrolysis condensation on the surface of the PLA membrane. Attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) were applied to analyse the surface chemistry and crystallization evolution, which confirmed that the P(VP-VTES) copolymer was hydrothermally crosslinked and induced the crystallization of the PLA membrane. The surface crystallization significantly improved the heat resistance and preserved membrane morphology, which was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and the dimension shrinkage. The modified PLA membrane with χc ∼ 37% remained almost unchanged dimensions and morphology even after annealing at 100 °C for 5 min. The improved hemocompatibility was verified by the prolonged clotting time and recalcification time, which was consistent with the enhanced hydrophilicity. All results showed that surface crosslinking induced crystallization strategy simultaneously improved the heat resistance and hemocompatibility, indicating a promising method for preparing robust and compatible PLA membranes.

The hemocompatibility of the dialysis membrane has been considered the key factor influencing the dialysis performance for curing the kidney malfunction. In this work, the commonly used anticoagulant heparin in the clinic was directly bonded to the poly(lactic acid) (PLA) membrane to improve the hemocompatibility via the glycidyl ether reaction. A novel precopolymer P(VP-VTES-GMA) was first prepared via free radical polymerization. The surface cross-linking of the precopolymer containing GMA segments enabled the membrane to anchor heparin through the glycidyl ether reaction. The chemical structure of the precopolymer was confirmed by 1H NMR. The surface chemistry was analyzed by XPS, toluidine blue staining, and solubility tests. The crystallization behavior, heat resistance, morphology, hydrophilicity, pore size, and pure water flux were investigated. The hemocompatibility was comprehensively investigated via APTT, PRT, PT, FIB, and platelet adhesion tests. The simulated dialysis performances relating to urea, creatinine, lysozyme, and BSA clearance were measured. All results demonstrated that the covalent bonding of heparin provided the PLA membrane with excellent hemcompatibility, hydrophilicity, heat resistance, and dialysis performance as well.Keywords: glycidyl ether reaction; hemocompatibility; heparin; PLA membrane;

•Novel dialysis membrane material PLLA.•Inter-connected bicontinuous structure of PLLA membrane was firstly prepared.•The unique effects of PEO on PLLA phase separation process.•Better solute clearance rate of PLLA membranes with bicontinuous structure.Poly (l-lactic acid) (PLLA) flat sheet membranes with inter-connected pores were prepared via non-solvent induced phase separation process. Polyethylene oxide (PEO) with molecule weight of 100 kD was used as additives. The morphology evolution from the partial to total inter-connected pores in cross section was accomplished by adjusting the PEO concentration. Besides, the effect of different molecule weight of polyethylene glycol (PEG), high coagulation intensity, different mass fraction ratios of PEO to PLLA and the casting solution exposure time in air on morphologies of PLLA membranes were also investigated respectively. Finally, as a hemodialysis membrane, the water permeability, solute clearance rate and mechanical properties were determined. It was shown that PLLA membrane with highly inter-connected pores exhibited a higher water flux of 225 L/hm2 and tensile strain of 83%. The clearance of the as-prepared membranes to urea and lysozyme is 77% and 33% respectively, while keeping BSA rejection with 90%.

•PVDF membrane showed stable superoleophobicity under seawater.•Excellent separation performances for oil/seawater emulsions were obtained.•PVDF membrane showed good fouling resistance and flux recovery.Under seawater superoleophobic polyvinylidene fluoride (PVDF) membrane inspired by mussel is successfully fabricated for both surfactant-free and surfactant-stabilized oil/seawater separation. The conventional PVDF membrane is modified by a simple solution-immersion method, which was immersed in dopamine aqueous solution for 24 h. The morphology and chemistry of dopamine inspired PVDF membrane was characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared spectra (FTIR-ATR) and X-ray photoelectron spectroscopy (XPS) respectively. The as-prepared membrane obtained stable superoleophobicity under seawater with an oil contact angle of 152±0.3° and extremely low oil-adhesion. Separation experiments for both surfactant-free and surfactant-stabilized emulsions showed that our membrane exhibited high oil/seawater separation efficiency (oil concentration in filtrate below 80 ppm) and substantially high permeability, which are several times higher than that current traditional filtration membrane. Fouling resistance to proteins was also investigated for long-term use purpose. This study provides a facile solution-immersion method to fabricate under seawater superoleophobic membrane, highlighting its great potential in practical oil/seawater separation.

•The zwitterionic PSBMA was grafted onto PLA membrane surface via ATRP.•Membrane zwitterionization improved its hydrophilicity and negativity.•The anti-fouling and hemocompatibility of PLA membranes were improved.•The modified PLA membrane showed good diafiltration performance.Poly(lactic acid) (PLA) hemodiafiltration membranes were grafted by zwitterionic polymer to improve the fouling resistance and hemocompatibility. The surface zwitterionization was accomplished by dopamine inspired bromoalkyl initiator anchoring and subsequent atom transfer radical polymerization (ATRP) of zwitterionic poly(sulfobetaine methacrylate) (PSBMA). Attenuated total reflectance Fourier transform infrared spectra (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were applied to analyze the surface chemistry and morphology evolution of the fabricated membranes, which confirmed that zwitterionic PSBMA was successfully grafted on PLA membrane. The results of water contact angle and zeta potentials demonstrated that the hydrophilicity and negativity of the modified PLA membranes were highly improved, which effectively alleviated the surface adsorption of bovine serum albumin (BSA) and palates. Moreover, the modified PLA membrane exhibited good dialysis performances. When the polymerization time of PSBMA was 1 h, the water flux was 184 L m−2 h−1, while BSA retention reached up to 90%, and the clearance of urea and creatinine was maintained at 66% and 60%, respectively. The present work provides a convenient strategy to improve the hydrophilicity, anti-fouling and hemocompatibility of PLA membranes for their biomedical and blood-contacting applications such as hemodialysis.

•PVP segments were firmly immobilized in the PVDF membrane due to the well-designed in situ cross-linking reaction.•The obtained membrane exhibited outstanding hydrophilicity and excellent antifouling property.•The newly-developed strategy can be extended to a universal approach to persistently hydrophilic microporous membrane.An in situ cross-linking route was developed to prepare persistently hydrophilic poly(vinylidene fluoride) (PVDF) membrane, which involved two key reactions, namely, copolymerization of N-vinyl-2-pyrrolidone (NVP) and triethoxyvinylsilane (VTES) and the subsequent hydrolysis condensation between the engineered poly(vinyl pyrrolidone) (PVP) chains. The overall idea of the new technique was to immobilize PVP segments in PVDF membrane via in situ cross-linking reaction and ultimately to obtain membrane with persistent hydrophilicity. Membrane properties were investigated in detail. Scanning Electron Microscopy (SEM) images unveiled that the modified membrane had discretely dotted pores in the surface with finger-like pores in the sublayers. Due to the high content of PVP segments immobilized in membrane surface, the membrane showed much better and more persistent hydrophilicity than the conventional PVDF/PVP blend membranes, as demonstrated by Atom Force Microscopy (AFM) and water contact angle measurement results. Protein adsorption on membrane surface was considerably mitigated, as well as membrane fouling during filtration process. The technique is generic, as it can be used for preparation of other polymeric membranes.

Responsive materials with surfaces that have controllable oil wettability under water offer considerable potential in advanced applications. We have developed an economical and convenient method for constructing a superwetting polyvinylidene fluoride (PVDF) membrane, giving super-hydrophobicity under oil and super-oleophobicity under water. The membrane has been achieved by incorporating pH-responsive N,N-dimethylaminoethylmethacrylate (DMAEMA) hydrogels into PVDF using a combination of in situ polymerization and conventional phase separation. In pure or acidic water the poly-DMAEMA chains modify wettability by the protonation or deprotonation of their tertiary amine side-groups, affecting the wettability of the membrane under water. In addition, this responsive membrane has been utilized for the separation of surfactant-stabilized water-in-oil and oil-in-water emulsions. High flux and separation efficiency can be obtained, together with excellent antifouling properties, suggesting that the membranes will find wide application in the separation of oil and water systems.

Poly(lactic acid) (PLA) is a sustainable membrane candidate for liquid separation and purification. However, the inherent brittleness restrains its practical application, especially for a porous membrane with thin thickness and high porosity. We aim to prepare PLA membranes with controlled pore structure and dialysis performance with improved mechanical and thermal stability by incorporating polysulfone-graft-poly(lactic acid) (PSf-g-PLA) copolymer. Different from the common rubbery elastomer, the brush-like PSf-g-PLA copolymer with a rigid backbone chain and soft side chains was elaborately synthesized to toughen and modify PLA membranes via a phase inversion process. 1H NMR, FTIR and GPC were conducted to determine the structure and molecular weight of the PSf-g-PLA. The influences of chloromethylation substitution and the content of copolymer on the membrane microstructure, the mechanical and thermal stability, and the dialysis performance were investigated in detail. It was demonstrated that the modified PLA membrane exhibited a pure water flux of 54 L m−2 h−1, 95% rejection to BSA, and 65% and 18% clearance of urea and lysozyme, respectively. Besides, both mechanical and thermal stability of the modified PLA membrane were improved by incorporating brush-like PSf-g-PLA.

Poly(lactic acid) (PLA) has attracted growing attention as a sustainable and environmentally benign membrane material. The good biocompatibility/hemocompatibility is essential for hemodialysis membranes. To circumvent the inadequate hydrophilicity/biocompatibility/hemocompatibility, we have developed a feasible strategy that enables the persistent PEGylation on PLA membranes via micro-swelling and subsequent UV-initiated crosslinking of poly(ethylene glycol)diacrylate (PEGDA). The content of DMSO and PEGDA in the reaction solution was crucial to control the surface PEGylation kinetics. Besides, the influence of PEGylation on membrane chemistry, morphology, hydrophilicity, water flux and dynamic fouling resistance to BSA was investigated. It was demonstrated that the biocompatibility/hemocompatibility was significantly improved by the surface PEGylation in terms of reduced BSA adsorption, extended APTT and alleviative platelet adhesion.

A novel positively charged loose nanofiltration (NF) membrane was fabricated feasibly by UV-induced photografting polymerization of diallyl dimethyl ammonium chloride (DADMAC) on Polysulfone ultrafiltration membrane. A possible reaction mechanism was proposed that a linear chain structure and/or pyrrole like five-membered nitrogen heterocycles structure on the side chain were grafted to form the active barrier layer. NF membrane demonstrated a looser average pore size of 8.6 nm and positive charges surface. Owing to the nanoscale ultrathin nanoscale barrier layer and the combination of Donnan exclusion and steric hindrance, NF membrane exhibited good hydrophilicity, a high pure flux of 60 L/m2 h (0.5 MPa), a good salt rejection to Mg2+ (90.8%), Al3+ (94.0%), Ca2+ (91.5%), and a high dye rejection to methylene blue (99.4%) and congo red (100.0%) respectively. The salts rejection of NF membrane to different salts followed the order of AlCl3 > CaCl2 > MgCl2 > NaCl > LiCl > MgSO4 > Na2SO4. NF membrane showed certain fouling resistance to seawater and BSA solution. The grafting polymerization kinetics were comprehensively investigated including irradiation time, monomer concentration and irradiation intensity. X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurement were employed to investigate membrane chemistry, morphologies, and hydrophilicity.

•The tradeoff of Polysulfone ultrafiltration membrane was conquered by zeolite 4A.•The permeability was enhanced by fast flow paths in micro-channels.•The selectivity was kept high due to steric exclusion and Donnan effect.•The zeolite size must match the selective layer thickness.Pressure-driven ultrafiltration by porous membrane often encountered a tradeoff between permeability and selectivity due to the transport mechanism based on pore dimension. This paper aims to break through the tradeoff of Polysulfone (PSf) ultrafiltration membranes by incorporating specific zeolite 4A. The influences of particle size, micro-channel dimension, zeta potential and content of zeolite 4A on tradeoff were discussed. The morphological evolution investigated by Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM) showed that zeolites 4A embedded in the selective layer within the depth of less than 1 μm increased the surface roughness and improved the hydrophilicity. Thermal and mechanical stability were also evaluated by thermal gravimetric analysis (TGA) and tensile testing respectively. The filtration experiments showed that both pure water flux and rejection were simultaneously improved due to the morphology regulation, abundant nano-scale water flow channels, negatively charged membrane surfaces and precise embedding position of zeolite 4A in the membrane selective layer.Polysulfone membranes (Pb-1, Pb-2 and Pb-3) doped with increasing zeolites 4A content showed increased pure water flux and rejection to pepsin and BSA simultaneously compared to control membranes (Pa-1, Pa-2 and Pa-3). The tradeoff between permeability and selectivity was sorted out by the embedding of zeolite 4A with abundant nano-scale water flow channels, negative charges in the membrane selective layer.

A supercritical carbon dioxide (ScCO2) assisted phase inversion was developed to produce microporous poly(vinylidene fluoride) (PVDF) membranes whose morphology characteristics arise from both liquid-liquid demixing and solid-liquid demixing (crystallization). This result was confirmed by Fourier transform infrared spectroscopy (FTIR), from which both α and β crystals were found. As revealed by contact angle experiment, the PVDF membranes prepared via ScCO2 assisted phase inversion were more hydrophobic compared with the control membrane produced via conventional immersion-precipitation technique. In particular, the sample with 15 wt% PVDF prepared at 45 °C and 13 MPa exhibited a contact angle of 142°, which was mainly caused by the multilevel micro- and nano-structure. The effects of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and lithium chloride (LiCl) on the structures and crystal form were investigated. PVP promoted the formation of α phase crystal form, while PEG boosts the evolution of β phase. LiCl restrained the crystallization degree of PVDF membrane under ScCO2.

•Antibacterial PVDF hollow fibre was fabricated by doping Ag-loaded zeolites.•D7T3 membrane was constructed to achieve higher flux using co-solvent.•Membrane doped 1 wt% Ag-loaded zeolites displayed obvious antibacterial property.•The produced membrane showed good fouling resistance to BSA.This work describes the fabrication and characterization of antibacterial poly(vinylidene fluoride) (PVDF) hollow fibre membranes via phase inversion using dry-jet wet-spinning technique. Ag-loaded NaY zeolites were particularly synthesized and then doped with PVDF spinning solution to produce a novel antibacterial hollow fibre with enhanced antibacterial efficiency. The morphologies, crystal structures, and Ag+ loading of synthesized Ag-loaded NaY zeolites were analyzed by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD) and inductively coupled plasma-atomic emission spectrometry (ICP-AES), respectively. The antibacterial efficiencies of the prepared hollow fibre membranes against Escherichia coli (E. coli) were evaluated by halo zone test, E. coli suspension filtration test and adhesion test. The surface morphologies, pure water flux, hydrophilicity, tensile strength, through-pore size, resistance to BSA of antibacterial PVDF hollow fibre membrane were also investigated. All results demonstrated that PVDF hollow fibre fabricated by doping Ag-loaded zeolites showed excellent antibacterial property, high permeability and mechanical strength, indicating the promising application as the antibacterial ultra-filtration membranes.

Poly(vinylidene fluoride) (PVDF) membranes were prepared by an ultrasound assisted phase inversion process. The effect of ultrasonic intensity on the evolution of membrane morphology with and without the addition of pore former LiCl during precipitation process was comprehensively investigated. Besides the inter-diffusion between the solvent and nonsolvent, the ultrasonic cavitation was thought to have significant influences on phase inversion and the resultant membrane morphology. The mutual diffusion between water and solvent during the ultrasound assisted phase inversion process was measured. The crystalline structure was detected by wide angle X-ray diffractometer (WAXD). The thermal behavior was studied by differential scanning calorimeter (DSC). The mechanical strength, forward and reverse water flux, rejection to bovine serum albumin (BSA) and pepsin were also investigated. By the ultrasound assisted phase inversion method, ultra-filtration membrane was successfully prepared, which exhibited more preferable morphology, better mechanical property and more favorable permeability without sacrificing the rejection and thermal stability.Highlights► PVDF membranes were prepared by an ultrasound assisted phase inversion process. ► The membrane micro-structures were strongly dependent on ultrasonic intensity. ► Ultrasonic irradiation accelerated the mutual diffusion of water and DMF. ► MA3 with 300 W ultrasonic irradiation showed best filtration performance.

A method of obtaining a hydrophilic and antifouling poly(vinylidene fluoride) (PVDF) membrane is developed via in situ polymerisation of 2-hydroxyethyl methacrylate (HEMA) in PVDF solution and subsequent micro-phase separation. The immobilization of PHEMA in a PVDF membrane was verified by Fourier Transform Infrared Spectroscopy (FTIR) and 1H Nuclear Magnetic Resonance Spectroscopy (1H-NMR). X-ray Photoelectron Spectroscopy (XPS) studies further unveiled the enrichment of PHEMA on the PVDF membrane surfaces. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) images revealed that the modified membrane had a fibrous-like microstructure in the cross section and a porous top surface. Water contact angle measurement suggested that the modified membrane formed by in situ polymerisation and micro-phase separation possessed higher hydrophilicity than the control membrane formed by blending PVDF and pre-polymerised PHEMA. The protein fouling of the modified membrane was considerably alleviated and the dried membrane showed spontaneous wettability and excellent permeability. Based on Wide-Angle X-ray Diffraction (WAXD) and the above results, a possible membrane formation mechanism for the in situ polymerisation and subsequent micro-phase separation was proposed.

Polyvinylidene fluoride (PVDF) flat sheet membranes with inter-connected pores were prepared via a non-solvent assisted thermally induced phase separation (Nat-ips) process. Triethylphosphate (TEP) was used as the latent solvent to prepare the metastable PVDF casting solution. The asymmetric ultra- and symmetric micro‐filtration membranes were respectively prepared by adjusting the polymer concentration and quench bath composition. Finger-like pores were totally eliminated and highly inter-connected pores were formed in both membranes. The morphology, crystallization, and mechanical strength of PVDF membranes were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), and tensile strength testing respectively. The effective through-pore size and pore size distribution of PVDF membranes were investigated by a bubble-point method. Pure water flux, protein rejection and fouling resistance were measured to study the filtration performance. All results showed that PVDF membranes with highly inter-connected pores and unimodal pore size distribution could be readily prepared by the Nat-ips process. The ultra- and micro‐filtration PVDF membrane exhibited a pure water flux of 120 and 1860 L/m2 h with the corresponding effective through-pore size of 0.11 μm and 0.26 μm respectively.Highlights► A novel Nat-ips process was used to prepare PVDF membranes. ► PVDF membranes exhibit inter-connected pores and unimodal pore size distribution. ► The quench bath strength controls the skin layer and cross-section. ► The unique bi-continuous pore structure offered high flux and rejection.

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method. The focus of this paper was put on the effects of four specific solvents with different solubility power including hexamethylphosphoramide (HMPA), trimethylphosphate (TMP), N,N-dimethylformamide (DMF) and triethylphosphate (TEP) on membrane polymorphism. Polymorphism of PVDF membranes was analyzed by wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) respectively. All results revealed that the dissolution of PVDF in different solvents had a great influence on the membrane crystalline phase. The well dissolved PVDF solution tended to form α phase during phase inversion process while the poorly dissolved PVDF solution favored the formation of β phase. Furthermore, a soft coagulation bath was used during the phase inversion process to enhance the filtration permeability of the PVDF membranes. The fouling resistance to protein and mechanical properties of the membranes were also investigated.Highlights► PVDF membranes were prepared via the phase inversion method. ► PVDF membrane polymorphism is highly dependent on the solvent dissolving power. ► The well dissolved PVDF solution tended to form alpha phase. ► The poorly dissolved PVDF solution favored the formation of beta phase.

A method of obtaining a hydrophilic and antifouling poly(vinylidene fluoride) (PVDF) membrane is developed via in situ polymerisation of 2-hydroxyethyl methacrylate (HEMA) in PVDF solution and subsequent micro-phase separation. The immobilization of PHEMA in a PVDF membrane was verified by Fourier Transform Infrared Spectroscopy (FTIR) and 1H Nuclear Magnetic Resonance Spectroscopy (1H-NMR). X-ray Photoelectron Spectroscopy (XPS) studies further unveiled the enrichment of PHEMA on the PVDF membrane surfaces. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) images revealed that the modified membrane had a fibrous-like microstructure in the cross section and a porous top surface. Water contact angle measurement suggested that the modified membrane formed by in situ polymerisation and micro-phase separation possessed higher hydrophilicity than the control membrane formed by blending PVDF and pre-polymerised PHEMA. The protein fouling of the modified membrane was considerably alleviated and the dried membrane showed spontaneous wettability and excellent permeability. Based on Wide-Angle X-ray Diffraction (WAXD) and the above results, a possible membrane formation mechanism for the in situ polymerisation and subsequent micro-phase separation was proposed.

To overcome the surface instability of traditional polymeric membranes especially with superwetting behaviour, a robust superhydrophilic surface was fabricated with nano-TiO2 inlaid on a hierarchical polylactide (PLA) ultrafiltration membrane via a spin coating process. Distinctly different from most previously reported nano-particle involved polymeric membranes, both the micro-/nano-architecture of the PLA membrane and the size matched nano-particle assembly constructed the robust superhydrophilic interface mimicking coral tentacle predatory behavior. The rigid surface based on the flexible polymeric membrane with the hierarchical architecture showed robust superhydrophilicity and underwater superoleophobicity even after long-term water washing treatment, which was also verified by the morphology, contact angle, XPS and adhesive force in contrast to smooth membranes. The as-prepared PLA membrane showed excellent separation performance for varieties of oil/water mixtures with a robustly high permeate flux (above 950 L m−2 h−1 under 0.1 MPa) and oil rejection (above 99%) even after 10 cycles of operation. Besides, the superhydrophilic PLA membrane exhibited outstanding anti-protein fouling properties. The PLA membrane showed relatively high BSA and ink rejection as well as water flux recovery and continuous separation stability due to rigid interface strengthening effects. The unique interface combination strategy between functional nanoparticles and polymeric membranes provided a window of opportunity for constructing robust polymeric membranes for advanced applications e.g. oil/water separation, ion exchange, in membrane catalytic reactors etc.