Photografted thin polymer hydrogel layers on PES ultrafiltration membranes: characterization, stability, and influence on separation performance

A multiple covalent crosslinked soft hydrogel for bioseparation

A multiple covalent crosslinked gel of poly(acrylamide–acrylic acid) was synthesized by using acrylic acid and acrylamide both as a monomer and as a covalent crosslinker.

Slippery to Sticky Transition of Hydrophobic Nanochannels

Contrary to common intuition that hydrophobic surfaces trivially cause water to slip, we discover a slippery-to-sticky transition in tunable hydrophobic nanochannels. We demonstrate this remarkable phenomenon by bringing out hitherto unveiled interplay between ion inclusions in the water and the interfacial lattice configuration over molecular scales. The consequent alterations in frictional characteristics illustrate that so-called hydrophobic nanochannels can be switchable to manifest features that are otherwise typically associated with hydrophilicity, causing water to stick. Our proposition may bear immense consequences toward fluidically functionalizing a hydrophobic interface without necessitating elaborate surface treatment techniques, bringing in far-ranging implications in diverse applications ranging from nature to energy.

Treatment of table olive processing wastewaters using novel photomodified ultrafiltration membranes as first step for recovering phenolic compounds

Table olive processing wastewaters (TOPW) have high salt concentration and total phenolic content (TPC) causing many environmental problems. To reduce them, ultrafiltration (UF) was applied for treating TOPW. However, NaCl, which is the main responsible of salinity in TOPW, and phenols are small molecules that cannot be separated by conventional UF membranes. They have serious problems caused by fouling, which can be overcome using membrane modification techniques. For these reasons, photomodification may be an effective technique to obtain a stream rich in TPC due to the changes in membrane surface properties. UV-modification in the presence of two hydrophilic compounds (polyethylene glycol and aluminium oxide) was performed to achieve membranes with high reductions of organic matter and to keep the TPC as high as possible. Commercial polyethersulfone (PES) membranes of 30 kDa were used. Surface modification was evaluated using FTIR-ATR spectroscopy and membrane performance was studied by calculating the rejection ratios of colour, chemical oxygen demand (COD) and TPC. Results demonstrated that UF is a useful pre-treatment to reduce organic matter from TOPW, obtaining a permeate rich in TPC. PES/Al2O3 membranes displayed superior antifouling properties and rejection values, keeping high the TPC (>95%). Therefore, UF using modified membranes is an appropriate and sustainable technique for treating TOPW.

Chemically selective polymer substrate based direct isotope dilution alpha spectrometry of Pu

Quantification of actinides in the complex environmental, biological, process and waste streams samples requires multiple steps like selective preconcentration and matrix elimination, solid source preparations generally by evaporation or electrodeposition, and finally alpha spectrometry. To minimize the sample manipulation steps, a membrane based isotope dilution alpha spectrometry method was developed for the determination of plutonium concentrations in the complex aqueous solutions. The advantages of this method are that it is Pu(IV) selective at 3M HNO3, high preconcentration factor can be achieved, and obviates the need of solid source preparation. For this, a thin phosphate-sulfate bifunctional polymer layer was anchored on the surface of microporous poly(ethersulfone) membrane by UV induced surface grafting. The thickness of the bifunctional layer on one surface of the poly(ethersulfone) membrane was optimized. The thickness, physical and chemical structures of the bifunctional layer were studied by secondary ionization mass spectrometry (SIMS), scanning electron microscopy (SEM) and SEM-EDS (energy-dispersive spectroscopy). The optimized membrane was used for preconcentration of Pu(IV) from aqueous solutions having 3-4M HNO3, followed by direct quantification of the preconcentrated Pu(IV) by isotope dilution alpha spectrometry using (238)Pu spike. The chemical recovery efficiency of Pu(IV) was found to be 86±3% below Pu(IV) loading capacity (1.08 μg in 2×1 cm(2)) of the membrane sample. The experiments with single representative actinides indicated that Am(III) did not sorb to significant extent (7%) but U(VI) sorbed with 78±3% efficiency from the solutions having 3M HNO3 concentration. However, Pu(IV) chemical recovery in the membrane remained unaffected from the solution containing 1:1000 wt. proportion of Pu(IV) to U(VI). Pu concentrations in the (U, Pu)C samples and in the irradiated fuel dissolver solutions were determined. The results thus obtained were found to be in good agreement with those obtained by conventional alpha spectrometry, biamperometry and thermal ionization mass spectrometry.

Covalent crosslinked polyelectrolyte complex membrane with high negative charges towards anti-natural organic matter fouling nanofiltration

Removal of natural organic matter (NOM) from drinking water by membrane technology is attracting increasing attention.

Preparation and characterization of a polyethersulfone/polyaniline nanocomposite membrane for ultrafiltration and as a substrate for a gas separation membrane

PES/PANI nanocomposite membrane displayed excellent flux and antifouling property for UF. Meanwhile, PES/PANI non-woven fabrics supported membrane performed as a suitable substrate for gas separation membrane with PVAm selective layer.

Constructing a zwitterionic ultrafiltration membrane surface via multisite anchorage for superior long-term antifouling properties

A novel zwitterionic membrane surface was constructed which exhibited stable antifouling ability by the formation of multisite anchorage covalent bonds.

Development of Bench and Full-Scale Temperature and pH Responsive Functionalized PVDF Membranes with Tunable Properties

Temperature and pH responsive polymers (poly(N-isopropylacrylamide) (PNIPAAm), and polyacrylic acid, PAA) were synthesized in one common macrofiltration PVDF membrane platform by pore-filling method. The microstructure and morphology of the PNIPAAm-PVDF, and PNIPAAm-FPAA-PVDF membranes were studied by attenuated total reflectance Fourier transform infrared (ATR-FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The membrane pore size was controlled by the swelling and shrinking of the PNIPAAm at the temperature around lower critical solution temperature (LCST). The composite membrane demonstrated a rapid and reversible swelling and deswelling change within a small temperature range. The controllable flux makes it possible to utilize this temperature responsive membrane as a valve to regulate filtration properties by temperature change. Dextran solution (Mw=2,000,000g/mol, 26 nm diameter) was used to evaluate the separation performance of the temperature responsive membranes. The ranges of dextran rejection are from 4% to 95% depending on the temperature, monomer amount and pressure. The full-scale membrane was also developed to confirm the feasibility of our bench-scale experimental results. The full-scale membrane also exhibited both temperature and pH responsivity. This system was also used for controlled nanoparticles synthesis and for dechlorination reaction.

Preparation of Sulfobetaine-Grafted PVDF Hollow Fiber Membranes with a Stably Anti-Protein-Fouling Performance

Based on a two-step polymerization method, two sulfobetaine-based zwitterionic monomers, including 3-(methacryloylamino) propyl-dimethyl-(3-sulfopropyl) ammonium hydroxide (MPDSAH) and 2-(methacryloyloxyethyl) ethyl-dimethyl-(3-sulfopropyl) ammonium (MEDSA), were successfully grafted from poly(vinylidene fluoride) (PVDF) hollow fiber membrane surfaces in the presence of N,N′-methylene bisacrylamide (MBAA) as a cross-linking agent. The mechanical properties of the PVDF membrane were improved by the zwitterionic surface layers. The surface hydrophilicity of PVDF membranes was significantly enhanced and the polyMPDSAH-g-PVDF membrane showed a higher hydrophilicity due to the higher grafting amount. Compared to the polyMEDSA-g-PVDF membrane, the polyMPDSAH-g-PVDF membrane showed excellent significantly better anti-protein-fouling performance with a flux recovery ratio (RFR) higher than 90% during the cyclic filtration of a bovine serum albumin (BSA) solution. The polyMPDSAH-g-PVDF membrane showed an obvious electrolyte-responsive behavior and its protein-fouling-resistance performance was improved further during the filtration of the protein solution with 100 mmol/L of NaCl. After cleaned with a membrane cleaning solution for 16 days, the grafted MPDSAH layer on the PVDF membrane could be maintain without any chang; however, the polyMEDSA-g-PVDF membrane lost the grafted MEDSA layer after this treatment. Therefore, the amide group of sulfobetaine, which contributed significantly to the higher hydrophilicity and stability, was shown to be imperative in modifying the PVDF membrane for a stable anti-protein-fouling performance via the two-step polymerization method.

Emulsion-templated macroporous polymer/polymer composites with switchable stiffness

Emulsion templates containing monomers in both emulsion phases were used to manufacture polystyrene-co-divinylbenzene based polymerized high internal phase emulsions (polyHIPEs) which have been reinforced by poly(methacrylic acid) (polyMAA) and poly(dimethyl aminoethyl methacrylate) (polyDMAEMA). The morphology of the hydrogel-filled polyHIPEs is affected by the hydrogels synthesized in the aqueous emulsion phase. The pore structure of polyMAA-filled polyHIPEs is highly interconnected indicating the formation of a methacrylic acid-co-styrene copolymer at the oil/water interface of the emulsion templates during synthesis. However, polyDMAEMA-filled polyHIPEs are predominately closed celled and the pore walls are covered by grafted hydrogel. The ability of the hydrogel-filled polyHIPEs to absorb water decreased with increasing crosslinking density of the hydrogels. The dry hydrogel reinforced the polyHIPE scaffolds possessed higher elastic moduli and crush strengths than the control polyHIPEs. The reinforcing ability of the dry hydrogels was further enhanced by increasing their degree of crosslinking. However, the reinforcement could be “switched off” simply by hydrating the hydrogels. The switchable mechanical properties of the hydrogel-filled polyHIPEs could potentially be utilized in smart humidity sensor technology.

A molecular dynamics study on pH response of protein adsorbed on peptide-modified polyvinyl alcohol hydrogel

Molecular dynamics simulation of the protein adsorption on peptide modified PVA hydrogel and the response of hydrogel chains to different pHs.

Development and Control of Bacterial Biofilms on Dairy Processing Membranes

Membrane fouling is a major operational problem that leads to reduced membrane performance and premature replacement of membranes. Bacterial biofilms developed on reverse osmosis membranes can cause severe flux declines during whey processing. Various types of biological, physical, and chemical factors regulate the formation of biofilms. Extracellular polymeric substances produced by constitutive microflora provide an effective barrier for the embedded cells. Cultural and microscopic techniques also revealed the presence of biofilms with attached bacterial cells on membrane surfaces. Presence of biofilms, despite regular cleaning processes, reflects ineffectiveness of cleaning agents. Cleaning efficiency depends upon factors such as pH of the cleaning agent, temperature, pressure, cleaning agent dose, optimum cleaning time, and cross-flow velocity during cleaning. Among different cleaning agents, surfactants help to prevent bacterial attachment to surfaces by reducing the surface tension of water and interfacial tension between the layers. Enzymes mixed with surfactants and chelating agents can be used to penetrate the biofilm matrix formed by microbes. Recent studies have shown the role of quorum-sensing-based cell-to-cell signaling, which provides communication within bacterial cells to form a mature biofilm, and also the role of applying quorum inhibitors to prevent biofilm formation. Major cleaning applications are also summarized in Table .

Surface zwitterionization of expanded poly(tetrafluoroethylene) membranes via atmospheric plasma-induced polymerization for enhanced skin wound healing

Development of bioinert membranes to prevent blood clotting, tissue adhesion, and bacterial attachment is important for the wound healing process. In this work, two wound-contacting membranes of expanded poly(tetrafluoroethylene) (ePTFE) grafted with zwitterionic poly(sulfobetaine methacrylate) (PSBMA) and hydrophilic poly(ethylene glycol) methacrylate (PEGMA) via atmospheric plasma-induced surface copolymerization were studied. The surface grafting chemical structure, hydrophilicity, and hydration capability of the membranes were determined to illustrate the correlations between bioadhesive properties and wound recovery of PEGylated and zwitterionic ePTFE membranes. Bioadhesive properties of the membranes were evaluated by the plasma protein adsorption, platelet activation, blood cell hemolysis, tissue cell adhesion, and bacterial attachment. It was found that the zwitterionic PSBMA-grafted ePTFE membrane presented high hydration capability and exhibited the best nonbioadhesive character in contact with protein solution, human blood, tissue cells, and bacterial medium. This work shows that zwitterionic membrane dressing provides a moist environment, essential for "deep" skin wound healing observed from the animal rat model in vivo and permits a complete recovery after 14 days, with histology of repaired skin similar to that of normal skin tissue. This work suggests that the bioinert nature of grafted PSBMA polymers obtained by controlling grafting structures gives them great potential in the molecular design of antibioadhesive membranes for use in skin tissue regeneration.

Simple strategy to functionalize polymeric substrates via surface-initiated ATRP for biomedical applications

The functionalization of polymer surfaces via surface-initiated atom transfer radical polymerization (ATRP) is of crucial importance to prepare various functional materials. It is generally complicated to conduct ATRP on different organic material surfaces. In this work, a facile photoinduced one-step method was first developed for the covalent immobilization of ATRP initiators on the C-H group-containing substrates such as biaxially oriented polypropylene (BOPP). The C-H bonds of precise location of inert polymer surfaces were readily transferred to bromoalkyl initiator, followed by ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and glycidyl methacrylate (GMA), respectively, to produce the resultant patterned BOPP-g-P(DMAEMA) and BOPP-g-P(GMA) films. The epoxy groups of the P(GMA) microdomains can be aminated for covalently coupling IgG, while the P(DMAEMA) microdomains were used for immobilizing IgG via electronic interactions. The resultant IgG-coupled microdomains could interact with the corresponding target proteins, anti-IgG.

Biofouling of water treatment membranes: a review of the underlying causes, monitoring techniques and control measures

Biofouling is a critical issue in membrane water and wastewater treatment as it greatly compromises the efficiency of the treatment processes. It is difficult to control, and significant economic resources have been dedicated to the development of effective biofouling monitoring and control strategies. This paper highlights the underlying causes of membrane biofouling and provides a review on recent developments of potential monitoring and control methods in water and wastewater treatment with the aim of identifying the remaining issues and challenges in this area.