Zhuan Yi

HYDROPHILIC NANOFILTRATION MEMBRANES WITH SELF-POLYMERIZED AND STRONGLY-ADHERED POLYDOPAMINE AS SEPARATING LAYER *

Inspired by the self-polymerization and strong adhesion characteristics of dopamine in aqueous conditions, a novel hydrophilic nanofiltration (NF) membrane was fabricated by simply dipping polysulfone (PSf) ultrafiltration (UF) substrate in dopamine solution. The changes in surface chemical composition and morphology of membranes were determined by Fourier transform infrared spectroscopy (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experimental results indicated that the self-polymerized dopamine formed an ultrathin and defect-free barrier layer on the PSf UF membrane. The surface hydrophilicity of membranes was evaluated through water contact angle measurements. It was found that membrane hydrophilicity was significantly improved after coating a polydopamine (pDA) layer, especially after double coating. The dyes filtration experiments showed that the double-coated membranes were able to reject completely the dyes of brilliant blue, congo red and methyl orange with a pure water flux of 83.7 L/(m2·h) under 0.6 MPa. The zeta potential determination revealed the positively-charged characteristics of PSf/pDA composite membrane in NF process. The salt rejection of the membranes was characterized by 0.01 mmol/L of salts filtration experiment. It was demonstrated that the salts rejections followed the sequence: NaCl < Na2SO4 < MgSO4 < MgCl2 < CaCl2, and the rejection to CaCl2 reached 68.7%. Moreover, the composite NF membranes showed a good stability in water-phase filtration process.

Versatile antifouling polyethersulfone filtration membranes modified via surface grafting of zwitterionic polymers from a reactive amphiphilic copolymer additive

Here we describe the development of versatile antifouling polyethersulfone (PES) filtration membranes modified via surface grafting of zwitterionic polymers from a reactive amphiphilic copolymer additive. Amphiphilic polyethersulfone-block-poly(2-hydroxyethyl methacrylate) (PES-b-PHEMA) was beforehand designed and used as the blending additive of PES membranes prepared by phase inversion technique. The surface enriched PHEMA blocks on membrane surface acted as an anchor to immobilize the initiating site. Poly(sulfobetaine methacrylate) (PSBMA) were subsequently grafted onto the PES blend membranes by surface-initiated atom transfer radical polymerization (SI-ATRP). The analysis of surface chemistry confirmed the successful grafting of zwitterionic PSBMA brushes on PES membrane surface. The resulted PES-g-PSBMA membranes were capable of separating proteins from protein solution and oil from oil/water emulsion efficiently. Furthermore, the modified membranes showed high hydrophilicity and strongly antifouling properties due to the incorporation of well-defined PSBMA layer. In addition, the PES-g-PSBMA membranes exhibited excellent blood compatibility and durability during the washing process. The developed antifouling PES membranes are versatile and can find their applications in protein filtration, blood purification and oil/water separation, etc.

HYDROPHILIC MODIFICATION OF PPESK POROUS MEMBRANES VIA AQUEOUS SURFACE-INITIATED ATOM TRANSFER RADICAL POLYMERIZATION *

Hydrophilic surface modification of poly(phthalazinone ether sulfone ketone) (PPESK) porous membranes was achieved via surface-initiated atom transfer radical polymerization (ATRP) in aqueous medium. Prior to ATRP, chloromethyl groups were introduced onto PPESK main chains by chloromethylation. Chloromethylated PPESK (CMPPESK) was fabricated into porous membrane through phase inversion technique. Hydrophilic poly(poly(ethylene glycol) methyl ether methacrylate) (P(PEGMA)) brushes were grafted from CMPPESK membrane under the initiation of benzyl chloride groups on membrane surface. The results of Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the grafting of P(PEGMA) chains. Water contact angle measurements and protein adsorption experiments suggested that the hydrophilicity and anti-fouling ability of PPESK membrane were remarkably improved after the grafting of P(PEGMA) brushes. The addition of small amount of water in the reaction solvent apparently accelerated the progress of the grafting reaction. The use of CuCl2 in the catalyst system promoted the controllability of the ATRP reaction.

Ion Exchange and Antibiofouling Properties of Poly(ether sulfone) Membranes Prepared by the Surface Immobilization of Brønsted Acidic Ionic Liquids via Double-Click Reactions

Brønsted acidic ionic liquids (BAILs) are unique ionic liquids that display chemical structures similar to zwitterions, and they were typically used as solvents and catalysts. In this work, an imidazole-based BAIL monolayer was fabricated onto poly(ether sulfone) (PES) membranes via surface clicking reactions, and the multifunctionality, including ion exchange and biofouling resistance to proteins and bacteria, was demonstrated, which was believed to be one of few works in which BAIL had been considered to be a novel fouling resistance layer for porous membranes. The successful immobilization of the BAILs onto a membrane surface was confirmed by X-ray photoelectron spectroscopy analysis, contact angle measurement, and ζ potential determination. The results from Raman spectroscopy showed that, as a decisive step prior to zwitterion, the BAIL was deprotonated in aqueous solution, and biofouling resistance to proteins and bacteria was found. However, BAIL displayed ion exchange ability at lower pH, and surface hydrophilicity/hydrophobicity of membranes could be tuned on purpose. Our results have demonstrated that the BAIL grafted onto membranes will not only act as an antibiofouling barrier like zwitterions but also provide a platform for surface chemical tailoring by ion exchange, the property of which will become especially important in acidic solutions where the fouling resistance performances of zwitterions are greatly weakened.

Hemocompatible and antibacterial porous membranes with heparinized copper hydroxide nanofibers as separation layer.

Here we report the fabrication of a novel heparinized copper hydroxide (Cu(OH)2) nanofiberous membrane with satisfying hemocompatibility and antibacterial properties. The positively charged Cu(OH)2 nanofibers were prepared in a weakly alkaline copper nitrate solution in the presence of 2-aminoethanol. A heparin (Hep) solution was then added dropwise into the solution of nanofibers to immobilize negatively charged heparin onto the Cu(OH)2 nanofibers by electrostatic interaction. A composite Hep@Cu(OH)2 nanofiberous membrane was prepared by filtration and deposition of the heparinized nanofibers onto a polysulfone (PSF) porous membrane. Chemical composition analysis of membrane surface using X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of heparin on Cu(OH)2 nanofibers. The amount of immobilized heparin on nanofiberous membrane was determined by a colorimetric assay of toluidine blue dye and the results showed that the amount of immobilized heparin was strongly dependent on the heparin dosage in reaction solution. The results of contact angle measurement indicated that the hydrophilicity of Cu(OH)2 nanofiberous membranes was enhanced by the immobilization of heparin. The adhesion, activation and transmutation of platelets on Hep@Cu(OH)2 membrane were suppressed remarkably due to the introduction of heparin, which suggested that the Hep@Cu(OH)2 membranes had good hemocompatibility. In addition, Cu(OH)2 and Hep@Cu(OH)2 nanofiberous membranes exhibited very good antibacterial activities against Escherichia coli and Staphyloccocus aureus.

SUPERCRITICAL CARBON DIOXIDE ASSISTED SYNTHESIS OF AMPHIPHILIC GRAFT COPOLYMERS BASED ON POLY(STYRENE-CO-MALEIC ANHYDRIDE) WITH METHOXYL POLY(ETHYLENE GLYCOL) SIDE CHAINS

Supercritical carbon dioxide (scCO2) was used as a reaction medium in synthesizing amphiphilic graft copolymers composed of poly(styrene-co-maleic anhydride) (SMA) backbones and methoxyl poly(ethylene glycol) (MPEG) side chains via esterification. The synthesized copolymers were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), 1H-NMR, thermo-gravimetric analysis (TGA) and differential scanning calorimetric analysis (DSC). The gelation phenomenon was suppressed effectively by tuning reaction conditions. The influences of scCO2 temperature and pressure on the conversion of anhydride were investigated. It was found that the highest conversion ratio occurred at 80°C under a constant pressure of 14 MPa or 26 MPa. With the increase of scCO2 pressure, the conversion ratio increased first, and then leveled off. The conversion ratio of anhydride could be controlled by regulating the reaction conditions. It was also revealed that using low molecular weight MPEG brought a high conversion ratio of anhydride.