Lixin Xue

An Intelligent Superwetting PVDF Membrane Showing Switchable Transport Performance for Oil/Water Separation

A superamphiphilic poly(vinylidene fluoride) (PVDF) membrane with superoleophobicity under water and superhydrophobicity under oil is successfully prepared. Due to the switchable transport performance, the membrane is applicable to the separation of various oil-in-water and water-in-oil emulsions with a droplet size greater than 20 nm, and shows superior permeability and antifouling properties, as well as a high separation efficiency.

Hydrophilic poly(vinylidene fluoride) (PVDF) membrane by in situ polymerisation of 2-hydroxyethyl methacrylate (HEMA) and micro-phase separation

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.

Poly(Lactic Acid) Hemodialysis Membranes with Poly(Lactic Acid)-block-Poly(2-Hydroxyethyl Methacrylate) Copolymer As Additive: Preparation, Characterization, and Performance.

Poly(lactic acid) (PLA) hemodialysis membranes with enhanced antifouling capability and hemocompatibility were developed using poly(lactic acid)-block-poly(2-hydroxyethyl methacrylate) (PLA-PHEMA) copolymers as the blending additive. PLA-PHEMA block copolymers were synthesized via reversible addition-fragmentation (RAFT) polymerization from aminolyzed PLA. Gel permeation chromatography (GPC) and (1)H-nuclear magnetic resonance ((1)H NMR) were applied to characterize the synthesized products. By blending PLA with the amphiphilic block copolymer, PLA/PLA-PHEMA membranes were prepared by nonsolvent induced phase separation (NIPS) method. Their chemistry and structure were characterized with X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy (AFM). The results revealed that PLA/PLA-PHEMA membranes with high PLA-PHEMA contents exhibited enhanced hydrophilicity, water permeability, antifouling and hemocompatibility. Especially, when the PLA-PHEMA concentration was 15 wt %, the water flux of the modified membrane was about 236 L m(-2) h(-1). Its urea and creatinine clearance was more than 0.70 mL/min, lysozyme clearance was about 0.50 mL/min, BSA clearance was as less as 0.31 mL/min. All the results suggest that PLA-PHEMA copolymers had served as effective agents for optimizing the property of PLA-based membrane for hemodialysis applications.

A pH-responsive PVDF membrane with superwetting properties for the separation of oil and water

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.

Single ion solid-state composite electrolytes with high electrochemical stability based on a poly(perfluoroalkylsulfonyl)-imide ionene polymer

Composite single ion solid-state polymer electrolytes were prepared by blending lithiated poly(perfluoroalkylsulfonyl)imide (PFSILi) ionene with poly(ethylene oxide) (PEO) at various PFSILi contents. Their electrochemical performance was characterized by ionic conductivity, lithium ion transport number, cyclic voltammetry and galvanostatic cycling in batteries. The composite PEO–PFSI-25, containing 24.5% of PFSI, was found to have a maximum ionic conductivity of 1.76 × 10−4 S cm−1 at 80 °C. Because of the immobilization of the anionic perfluorosulfonimide groups on the backbone of the ionene polymer with flexible and stable perfluoroether connectors, the composite had unusually high electrochemical stability (up to 5.5 V vs. Li+/Li) and a low anion transference number. The PFSILi unit interacts strongly with the PEO segments, resulting in the depression of PEO crystallization and the formation of multi-dimensional ionic crosslinks within the composite to impart dimensional and cycling stability to the electrolyte system. LiFePO4/Li battery prototypes using PEO–PFSILi polymer electrolytes, with reversible capacity of 140 mA h g−1 at 80 °C and 0.2 °C, were able to maintain 50 stable cycles for 1000 h at 70 °C and 0.1 °C.

Mixed matrix membranes containing MIL-53(Al) for potential application in organic solvent nanofiltration

Aromatic poly(m-phenyleneisophthalamide) (PMIA) and the metal-organic framework (MOF) MIL-53(Al) were employed as the polymer matrix and additive, respectively, to develop mixed matrix membranes (MMMs) via non-solvent induced phase separation for potential application in organic solvent nanofiltration. The prepared membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and water contact angle measurements. The membrane water permeance enhanced when MIL-53(Al) was incorporated into the membrane structure while the rejection had no significant change. The optimum MMM (with 0.5 wt% MOF concentration) passes mono and bivalent inorganic salts but rejects larger charged organic molecules and has a mean effective pore size of 0.7 nm. The influence of organic solvents on MMM performance was also investigated and the result shows that the performance shifts towards a lower pure water permeance and a higher rejection after exposure to organic solvents (ethyl acetate or methanol). The membrane performance in organic solvent nanofiltration was evaluated on the basis of the permeance and rejection of brilliant blue G in ethanol, and the result showed that the permeance of MMMs significantly increased (by 289%) while the rejection slightly reduced by 4% in contrast to the pure membrane.

Facile preparation of patterned petal-like PLA surfaces with tunable water micro-droplet adhesion properties based on stereo-complex co-crystallization from non-solvent induced phase separation processes

A facile method to prepare rose petal-like quasi-superhydrophobic poly(lactide) (PLA) membrane surfaces with tunable water droplet adhesion properties based on the stereo-complex co-crystallization of PLAs via non-solvent induced phase separation processes is reported. The co-crystallization of the D- and L-enantiomer of PLA on the bottom surfaces contacting the base glass has led to the formation of hierarchical microstructures containing half-developed to well-developed micrometer-scale papilla or spheres and nanometer-scale folds depending on the thickness of the primary membranes. The bottom surfaces of thinner PLA membranes with primary thicknesses of 100–200 micrometers containing half-developed smaller microspheres and a wider gap space could firmly pin water droplets even upside down with an extremely high adhesion force of about 118–132 μN with water drop breakup, while the bottom surfaces of thicker PLA membranes with a primary thickness of 300–500 micrometers containing larger well developed microspheres with narrower gap space could allow the rolling of water droplets with lower adhesion forces of 74–99 μN. Strategies were developed to create patterned PLA quasi-superhydrophobic membrane surfaces with zoned water droplet adhesion properties for controllable micro-droplet transportation and potentially image encrypting applications.

Improvement in LiFePO4–Li battery performance via poly(perfluoroalkylsulfonyl)imide (PFSI) based ionene composite binder

Lithiated poly(perfluoroalkylsulfonyl)imide (PFSILi) ionene is synthesized and blended with poly(vinylidene) difluoride (PVDF) to serve as binder for the electrode of a lithium ion battery. The incorporation of the PFSILi ionene adds ionic conducting channels inside the electrodes and prevents electrolyte depletion during rapid charging–discharging. The small composition change results in an increase in the battery performance, including a better reversibility, lower polarization or internal resistance and an improved discharge capacity, as well as a higher energy density at high rates or elevated temperatures. At the rate of 2 C and 60 °C, the discharge plateau potential for the cell with the ionene based binder is 0.29 V higher than that for the cell with a PVDF only cathode binder. At a 4 C rate, the discharge capacity and energy density of a LiFePO4–Li half-cell with the ionic binder are 50% and 66%, respectively, higher than those of the cell using the nonionic PVDF binder at room temperature. Thus, the ionene polymer offers a new route, rather than just altering the active materials, to overcome the limitations of capacity and power density for rechargeable lithium batteries.

Poly(vinylidene fluoride) membranes by an ultrasound assisted phase inversion method

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.

Polysulfone hemodiafiltration membranes with enhanced anti-fouling and hemocompatibility modified by poly(vinyl pyrrolidone) via in situ cross-linked polymerization

Poly(vinyl pyrrolidone) (PVP) and its copolymers have been widely employed for the modification of hemodiafiltration membranes due to their excellent hydrophilicity, antifouling and hemocompatibility. However, challenges still remain to simplify the modification procedure and to improve the utilization efficiency. In this paper, antifouling and hemocompatibility polysulfone (PSf) hemodiafiltration membranes were fabricated via in situ cross-linked polymerization of vinyl pyrrolidone (VP) and vinyltriethoxysilane (VTEOS) in PSf solutions and non-solvent induced phase separation (NIPS) technique. The prepared membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), which suggested that VP and VTEOS have been cross-linked copolymerized in PSf membranes. The modified PSf membranes with high polymer content showed improved hydrophilicity, ultrafiltration and protein antifouling ability. In addition, the modified PSf membranes showed lower protein adsorption, inhibited platelet adhesion and deformation, prolonged the activated partial thromboplastin time (APTT), prothrombin time (PT), and decreased the content of fibrinogen (FIB) transferring to fibrin, indicating enhanced hemocompatibility. In a word, the present work provides a simple and effective one-step modification method to construct PSf membranes with improved hydrophilicity, antifouling and hemocompatibility.