A switchable zwitterionic membrane surface chemistry for biofouling control

Zwitterionic-enhanced hyperbranched polysiloxane membrane with advanced anti-crude oil fouling for high-efficient oil-in-water emulsion separation

Membrane fouling, attributed to the adhesion of oil droplets, presents a significant challenge to membrane separation technology. The hydrophilic surface modification of polymer membranes has been proven as an effective antifouling strategy. Here, a novel zwitterionic hyperbranched polysiloxane modificated membrane (ZHBPSi@PDA@M) was synthesized through oxidative self-polymerization to form the polydopamine (PDA) adhesion layer, Michael addition, and ring-opening reaction. The surface of ZHBPSi@PDA@M achieved the superhydrophilic modification, acquiring an underwater oil contact angle of 158.6°. Furthermore, the membrane had a high water permeance of 13,924 L m-2 h-1 bar-1, representing a 29-fold increase compared to the nascent membrane, and achieved excellent separation of various oil-in-water emulsions, with permeance and rejection efficiency of 5534 L m-2 h-1 bar-1 and 99.9 %, respectively. Additionally, the ZHBPSi@PDA@M not only achieved excellent acid-base stability, but also possessed good self-cleaning and anti-fouling properties. Moreover, the composite membrane effectively separated crude oil emulsions, achieving a permeance of 3986 L m-2 h-1 bar-1 and a separation efficiency of 98.3 %, thereby offering a novel approach for the treatment of high-viscosity oil-containing wastewater.

Fighting against biofilm: The antifouling and antimicrobial material

Biofilms are groups of microorganisms protected by self-secreted extracellular substances. Biofilm formation on the surface of biomaterial or engineering materials becomes a severe challenge. It has caused significant health, environmental, and societal concerns. It is believed that biofilms lead to life-threatening infection, medical implant failure, foodborne disease, and marine biofouling. To address these issues, tremendous effort has been made to inhibit biofilm formation on materials. Biofilms are extremely difficult to treat once formed, so designing material and coating bearing functional groups that are capable of resisting biofilm formation has attracted increasing attention for the last two decades. Many types of antibiofilm strategies have been designed to target different stages of biofilm formation. Development of the antibiofilm material can be classified into antifouling material, antimicrobial material, fouling release material, and integrated antifouling/antimicrobial material. This review summarizes relevant research utilizing these four approaches and comments on their antibiofilm properties. The feature of each method was compared to reveal the research trend. Antibiofilm strategies in fundamental research and industrial applications were summarized.

Extracellular Vesicle-Mediated Modulation of Stem-like Phenotype in Breast Cancer Cells under Fluid Shear Stress

Circulating tumor cells (CTCs) are some of the key culprits that cause cancer metastasis and metastasis-related deaths. These cells exist in a dynamic microenvironment where they experience fluid shear stress (FSS), and the CTCs that survive FSS are considered to be highly metastatic and stem cell-like. Biophysical stresses such as FSS are also known to cause the production of extracellular vesicles (EVs) that can facilitate cell-cell communication by carrying biomolecular cargos such as microRNAs. Here, we hypothesized that physiological FSS will impact the yield of EV production, and that these EVs will have biomolecules that transform the recipient cells. The EVs were isolated using direct flow filtration with and without FSS from the MDA-MB-231 cancer cell line, and the expression of key stemness-related genes and microRNAs was characterized. There was a significantly increased yield of EVs under FSS. These EVs also contained significantly increased levels of miR-21, which was previously implicated to promote metastatic progression and chemotherapeutic resistance. When these EVs from FSS were introduced to MCF-7 cancer cells, the recipient cells had a significant increase in their stem-like gene expression and CD44+/CD24- cancer stem cell-like subpopulation. There was also a correlated increased proliferation along with an increased ATP production. Together, these findings indicate that the presence of physiological FSS can directly influence the EVs' production and their contents, and that the EV-mediated transfer of miR-21 can have an important role in FSS-existing contexts, such as in cancer metastasis.

Preparation and characterization of clay based ceramic porous membranes and their use for the removal of lead ions from synthetic wastewater with an insight into the removal mechanism

The present study explores the use of local clay from the United Arab Emirates (UAE) to prepare porous ceramic membranes (flat disk shape) for the purpose of removing toxic heavy metals from contaminated water. Four distinct ceramic membranes, crafted from locally sourced clay and incorporated with activated carbon and graphite, underwent careful and thorough preparation. The initial set of membranes was subjected to open-air sintering, resulting in the creation of mACA and mGrA membranes. Concurrently, a second set of meticulously prepared membranes underwent sintering under inert nitrogen conditions, yielding the formation of mACI and mGrI membranes, respectively. Prior to making the membranes, the clay material was characterized by thermogravimetric analysis (TGA), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction analysis (XRD). The clay presented the lowest weight loss compared to AC and Gr, implying that these two materials could be used as porogen agents. The X-ray fluorescence results indicated that the natural clay contained 65.5 wt% of silicon dioxide (SiO2), aluminium oxide (Al2O3), and iron (III) oxide (Fe2O3) falling within the class C category of clays according to ASTM. The FTIR analysis showed different clay regions allocated to various stretching and deformation vibrations of hydroxide, organic fraction, and (Si, Al, Fe)-O groups. The XRD analysis revealed the presence of kaolinite, illite, smectite and calcite phyllite phases in the clay mineral. The membranes were characterized using FESEM, with those containing AC (used as porogen) exhibiting large pores clearly visible on the surface, and were tested for the removal of lead (Pb2+) ions from synthetic wastewater. The removal efficiencies of the membranes were 33 %, 75.2 %, 100 % and 100 % for mACA, mACI, mGrA and mGrI respectively after 100 min operation. The wettability of the membranes was found to follow the order mACI < mACA < mGrI < mGrA, which corroborated well with water fluxes of 7, 8, 112 and 214 L h-1 m-2 recorded after 60 min duration and 1.0 bar applied pressure. The mechanisms of filtration of Pb2+ ions were adsorption for the AC-based membranes (mACA, mACI) and a combination of adsorption and size exclusion for the Gr-based membranes (mGrA, mGrI).

Amphiphilic Polyampholytes for Fouling-Resistant and Easily Tunable Membranes

The versatility of membranes is limited by the narrow range of material chemistries on the market, which cannot address many relevant separations. Expanding their use requires new membrane materials that can be tuned to address separations by providing the desired selectivity and robustness. Self-assembly is a versatile and scalable approach to create tunable membranes with a narrow pore size distribution. This study reports the first examples of a new class of membrane materials that derives state-of-the-art permeability, selectivity, and fouling resistance from the self-assembly of random polyampholyte amphiphilic copolymers. These membranes feature a network of ionic nanodomains that serve as nanochannels for water permeation, framed by hydrophobic nanodomains that preserve their structural integrity. This copolymer design approach enables precise selectivity control. For example, sodium sulfate rejections can be tuned from 5% to 93% with no significant change in the pore size or fouling resistance. Membranes developed here have potential applications in wastewater treatment and chemical separations.

Preparation and Characterization of Polyethersulfone-Ultrafiltration Membrane Blended with Terbium-Doped Cerium Magnesium Aluminate: Analysis of Fouling Behavior

In this study, various techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and water-contact-angle goniometry (WCAG), were used to characterize the crystalline structure and morphological properties of terbium-doped cerium magnesium aluminate (Ce0.67Tb0.33MgAl11O19 or CMAT) in powder form. The results demonstrated that CMAT was successfully synthesized with a particle size of less than 5 µm and a fully evident distribution of elements, as revealed by the SEM images. This was further confirmed by the XRD and HRTEM images. XPS analysis confirmed the presence of all necessary components in CMAT. Additionally, WCAG results showed that the contact angle of CMAT was more hydrophilic with a value of 8.4°. To evaluate its performance, CMAT particles were dispersed in a Polyethersulfone (PES) solution and used to modify a PES ultrafiltration membrane through a phase-inversion method. The resulting membranes were characterized by SEM, atomic force microscopy (AFM), thermogravimetric analysis (TGA), WCAG, and permeability performance and fouling experiments. The addition of CMAT to the PES membranes did not have a significant effect on the structure of the SEM images of the top layer and cross-section of surface properties. However, increasing the concentration of CMAT improved the membrane surface roughness in AFM, and the modified membranes had the ability to resist fouling. The addition of CMAT did not lead to significant energy loss, indicating that the heat flux loss observed can indeed be explained by the amount of C-OH on the PES membrane’s surface. The contact angle of the membranes became more hydrophilic with increasing concentration of CMAT from PES G0 to PES G7. The PES origin membrane showed a higher permeation than the membranes mixed with CMAT, and the modified membranes with CMAT displayed significant fouling resistance.

Poly(vinylidene fluoride)/partially alkylated poly(vinyl imidazole) interpolymer ultrafiltration membranes with intrinsic anti-biofouling and antifouling property for the removal of bacteria

Bacterial contaminated water causes potential health issues. Conventional chlorine treatment has shortcomings of environmental hazards and chlorine adoptability by the bacterial cells. Ultrafiltration membrane can intercept bacterial species from feed water. Membrane having anti-biofouling/antifouling properties is needed for the removal of bacteria from feed water. Herein, interpolymer membranes with inherent antimicrobial activity and fouling release property have been prepared by the blend of poly(vinylidene fluoride) (PVDF), poly(vinyl pyrrolidone) and partially long chain alkylated (C12 chain) poly(vinyl imidazole) copolymer (PVIm-co-PVIm-C12) followed by cross-linking of the remaining VIm groups with an activated di-halide compound. The membranes obtain with copolymers of degree of alkyl substitution (DS_C12) in the range of 0.75-0.85 and amount in the range of 0.9-3.5% w/w in the casting solutions exhibit good antimicrobial activity (>99 % of inhibition) and dynamic anti-biofouling property. The membrane prepared with 0.9% w/w of the copolymer (DS_C12=0.85) shows higher flux recovery ratio (91 % for bacterial filtration and 88 % for protein filtration) compare to a pristine membrane (57 % for bacterial filtration and 58 % for protein filtration). The membrane is able to reject the bacteria completely. Use of small amount of copolymer and facile fabrication of stable anti-biofouling/antifouling membranes show potential for the purification of bacterial contaminated water.

Biofouling-Resistant Ultrafiltration Membranes via Codeposition of Dopamine and Cetyltrimethylammonium Bromide with Retained Size Selectivity and Water Flux

Biofouling is a serious problem in ultrafiltration (UF) membrane applications. Modifying the surface of membranes with low molecular weight, commercially available antibacterial chemistries is an excellent strategy to mitigate biofouling. Herein, we report a new strategy to impart antibacterial and anti-biofouling behavior without changing the support membrane's size selectivity and pure water permeance (PWP). To this end, a strong antibacterial agent, cetyltrimethylammonium bromide (CTAB), was codeposited with dopamine onto commercial polyethersulfone (PES) UF membranes in the presence of nitrogen (N₂) gas backflow. The PWP and pore size of the support membrane did not change with codeposition, confirming the benefit of N₂ backflow in mitigating the solution intrusion phenomenon. X-ray photoelectron spectroscopy (XPS), surface ζ potentials, and contact angle measurements confirmed the successful codeposition of polydopamine (PDA) and CTAB onto the membrane. Among three different CTAB concentrations systematically investigated, the membrane functionalized with CTAB at the critical micelle concentration (CMC) provided the best anti-biofouling activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria and retained its surface ζ potential after being stored in 1 M NaCl (pH = 6.8) for 3 months. Our results demonstrate the potential of using a facile, one-step approach to modify commercial UF membranes without compromising their pore size or flux, while simultaneously endowing antibacterial activity.

Efficient Retention and Alpha Spectroscopy of Actinides from Aqueous Solutions Using a Combination of Water-Soluble Star-like Polymers and Ultrafiltration Membranes

We explored two approaches to recover uranium and plutonium from aqueous solutions at pH 4 and pH 7 using water-soluble star-like polyacrylamide polymers with a dextran core. In the first approach, a solution comprising a neutral or ionomer polymer was mixed with a radionuclide solution to form polymer–metal complexes that were then retained by ultrafiltration (UF) membranes under applied pressure. The same polymers were first deposited on the membrane in the second approach using pressure-driven flow. The applied polymers had an overall diameter of gyration of 120 nm, which exceeded the nominal diameter of the UF membrane pores. The polymers showed a high affinity to uranyl but could also be used to extract Pu from neutral or near-neutral pH solutions. Direct-flow single-step filtration and alpha spectrometry demonstrated that the UF membranes containing star-like copolymers could recover 99% of U and up to 60% of Pu from deionized water after filtering 15 mL solutions containing 25 ppm and 33 ppb of the actinides, correspondingly. The sorption capacity of the polymers for uranium could be measured as 1mg U per mg of the polymer after six subsequent filtration steps. Alpha spectroscopy of the deposited actinides revealed peculiarities of the structural organization of polymers and their complexes with U or Pu, depending on the approach. Though both approaches were efficient, the second approach (deposition of the polymer on the membrane followed by filtration) has an additional advantage of protecting the membrane pores from capillary collapse by filling them with the polymer chains. Therefore, these polymer-modified membranes could be used either in continuous or multi-step filtration process with drying after each step without deterioration of their sorption characteristics.

Fouling Prevention in Polymeric Membranes by Radiation Induced Graft Copolymerization

The application of membrane processes in various fields has now undergone accelerated developments, despite the presence of some hurdles impacting the process efficiency. Fouling is arguably the main hindrance for a wider implementation of polymeric membranes, particularly in pressure-driven membrane processes, causing higher costs of energy, operation, and maintenance. Radiation induced graft copolymerization (RIGC) is a powerful versatile technique for covalently imparting selected chemical functionalities to membranes' surfaces, providing a potential solution to fouling problems. This article aims to systematically review the progress in modifications of polymeric membranes by RIGC of polar monomers onto membranes using various low- and high-energy radiation sources (UV, plasma, γ-rays, and electron beam) for fouling prevention. The feasibility of the modification method with respect to physico-chemical and antifouling properties of the membrane is discussed. Furthermore, the major challenges to the modified membranes in terms of sustainability are outlined and the future research directions are also highlighted. It is expected that this review would attract the attention of membrane developers, users, researchers, and scientists to appreciate the merits of using RIGC for modifying polymeric membranes to mitigate the fouling issue, increase membrane lifespan, and enhance the membrane system efficiency.

Effect of Nanopatterning on Concentration Polarization during Nanofiltration

Membranes used for desalination still face challenges during operation. One of these challenges is the buildup of salt ions at the membrane surface. This is known as concentration polarization, and it has a negative effect on membrane water permeance and salt rejection. In an attempt to decrease concentration polarization, a line-and-groove nanopattern was applied to a nanofiltration (NF) membrane. Aqueous sodium sulfate (Na2SO4) solutions were used to test the rejection and permeance of both pristine and patterned membranes. It was found that the nanopatterns did not reduce but increased the concentration polarization at the membrane surface. Based on these studies, different pattern shapes and sizes should be investigated to gain a fundamental understanding of the influence of pattern size and shape on concentration polarization.

Zwitterionic Polysulfone Copolymer/Polysulfone Blended Ultrafiltration Membranes with Excellent Thermostability and Antifouling Properties

Membrane fouling has been one of the most important challenges in membrane separation operations. In this study, we report a facile strategy to prepare antifouling polysulfone (PSf) UF membranes by blending amphiphilic zwitterion polysulfone-co-sulfobetaine polysulfone (PSf-co-SBPSf) copolymer. The copolymer chemical structure was characterized by ¹HNMR spectroscopy. The PSf/PSf-co-SBPSf blend membranes with various zwitterionic SBPSf segment contents exhibited better surface hydrophilicity and excellent antifouling ability compared to PSf and PSf/PEG membranes. The significant increase of both porosity and water permeance indicates that the PSf-co-SBPSf has a pore-forming effect. The pure water flux and flux recovery ratio of the PSf/PSf-co-SBPSf blend membranes were both remarked to improve 286.43 L/m²h and 92.26%, while bovine serum albumin (BSA) rejection remained at a high level (97.66%). More importantly, the water flux and BSA rejection see minimal variance after heat treatment, indicating excellent thermostability. Overall, the PSf/PSf-co-SBPSf blend membranes achieved a comprehensive performance of sustainable hydrophilic, high permeation flux, and remarkable antifouling ability, thus becoming a promising candidate in high-temperature separation application.

Evaluating Protein Fouling on Membranes Patterned by Woven Mesh Fabrics

Membrane surface patterning is one approach used to mitigate fouling. This study used a combination of flux decline measurements and visualization experiments to evaluate the effectiveness of a microscale herringbone pattern for reducing protein fouling on polyvinylidene fluoride (PVDF) ultrafiltration membranes. Thermal embossing with woven mesh stamps was used for the first time to pattern membranes. Embossing process parameters were studied to identify conditions replicating the mesh patterns with high fidelity and to determine their effect on membrane permeability. Permeability increased or remained constant when patterning at low pressure (≤4.4 MPa) as a result of increased effective surface area; whereas permeability decreased at higher pressures due to surface pore-sealing of the membrane active layer upon compression. Flux decline measurements with dilute protein solutions showed monotonic decreases over time, with lower rates for patterned membranes than as-received membranes. These data were analyzed by the Hermia model to follow the transient nature of fouling. Confocal laser scanning microscopy (CLSM) provided complementary, quantitative, spatiotemporal information about protein deposition on as-received and patterned membrane surfaces. CLSM provided a greater level of detail for the early (pre-monolayer) stage of fouling than could be deduced from flux decline measurements. Images show that the protein immediately started to accumulate rapidly on the membranes, likely due to favorable hydrophobic interactions between the PVDF and protein, followed by decreasing rates of fouling with time as protein accumulated on the membrane surface. The knowledge generated in this study can be used to design membranes that inhibit fouling or otherwise direct foulants to deposit selectively in regions that minimize loss of flux.

A review on surface modification methods of poly(arylsulfone) membranes for biomedical applications

Considerable methods have so far been used for the surface modification of biomedical membranes. Several reviews and articles have been published on the improvements achieved in the field of poly(arylsulfone) membranes subjected to various surface modification methods and used in biomedical applications. This review concentrates on the surface modification, biological applications and future perspective of the poly(arylsulfone) biomedical membranes. Different surface modification procedures employed for the poly(arylsulfone) membranes have been classified, studied and compared. Diverse surface modification techniques include surface coating, chemical modification and immobilization/cross-linking, grafting, surface zwitterionicalization, mussel-inspired coating and layer-by-layer assembly. Furthermore, we review the recent research studies performed on the surface modification of the poly(arylsulfone) biomedical membranes. Meanwhile, the properties of biomedical membranes are also discussed in each section. At last, the future perspective and challenges of the strategies utilized for the surface modification of poly(arylsulfone) biomedical membranes are presented.

Initial Deposition and Pioneering Colonization on Polymeric Membranes of Anaerobes Isolated from an Anaerobic Membrane Bioreactor (AnMBR)

Membrane biofouling constitutes a great challenge in anaerobic membrane bioreactor (AnMBR). Here, we studied the initial deposition of anaerobes, the first step in biofilm formation, with a consortium isolated from an AnMBR on membranes with different surface properties and under two shear rate conditions without filtration. We found that the cell transfer coefficient, calculated from the initial deposition experiments, was similar under the two shear rates for the hydrophobic membranes, but much higher under low shear rate and much lower under high shear rate, for the hydrophilic membrane. The cell transfer coefficient measured under filtration mode and at a higher shear rate showed a similar trend. The pioneer bacteria and archaea (without filtration) were identified by next-generation sequencing. The results showed that the selective force for the dissimilarity of the pioneer bacterial and archaeal diversity was the shear rate and the membrane surface properties, respectively. However, statistical analyses revealed minor changes in the pioneer bacteria (class level) and archaea (order level) populations under the various conditions. These results shed light on the first step of biofilm formation on the membranes in AnMBRs and emphasize the importance of hydrodynamic shear and membrane surface properties on the initially deposited anaerobes.

Superhydrophilicity and strong salt-affinity: Zwitterionic polymer grafted surfaces with significant potentials particularly in biological systems

In recent years, zwitterionic polymers have been frequently reported to modify various surfaces to enhance hydrophilicity, antifouling and antibacterial properties, which show significant potentials particularly in biological systems. This review focuses on the fabrication, properties and various applications of zwitterionic polymer grafted surfaces. The "graft-from" and "graft-to" strategies, surface grafting copolymerization and post zwitterionization methods were adopted to graft lots type of the zwitterionic polymers on different inorganic/organic surfaces. The inherent hydrophilicity and salt affinity of the zwitterionic polymers endow the modified surfaces with antifouling, antibacterial and lubricating properties, thus the obtained zwitterionic surfaces show potential applications in biosystems. The zwitterionic polymer grafted membranes or stationary phases can effectively separate plasma, water/oil, ions, biomolecules and polar substrates. The nanomedicines with zwitterionic polymer shells have "stealth" effect in the delivery of encapsulated drugs, siRNA or therapeutic proteins. Moreover, the zwitterionic surfaces can be utilized as wound dressing, self-healing or oil extraction materials. The zwitterionic surfaces are expected as excellent support materials for biosensors, they are facing the severe challenges in the surface protection of marine facilities, and the dense ion pair layers may take unexpected role in shielding the grafted surfaces from strong electromagnetic field.

Zwitterion Co-Polymer PEI-SBMA Nanofiltration Membrane Modified by Fast Second Interfacial Polymerization

Nanofiltration membranes have evolved as a promising solution to tackle the clean water scarcity and wastewater treatment processes with their low energy requirement and environment friendly operating conditions. Thin film composite nanofiltration membranes with high permeability, and excellent antifouling and antibacterial properties are important component for wastewater treatment and clean drinking water production units. In the scope of this study, thin film composite nanofiltration membranes were fabricated using polyacrylonitrile (PAN) support and fast second interfacial polymerization modification methods by grafting polyethylene amine and zwitterionic sulfobutane methacrylate moieties. Chemical and physical alteration in structure of the membranes were characterized using methods like ATR-FTIR spectroscopy, XPS analysis, FESEM and AFM imaging. The effects of second interfacial polymerization to incorporate polyamide layer and ‘ion pair’ characteristics, in terms of water contact angle and surface charge analysis was investigated in correlation with nanofiltration performance. Furthermore, the membrane characteristics in terms of antifouling properties were evaluated using model protein foulants like bovine serum albumin and lysozyme. Antibacterial properties of the modified membranes were investigated using E. coli as model biofoulant. Overall, the effect of second interfacial polymerization without affecting the selectivity layer of nanofiltration membrane for their potential large-scale application was investigated in detail.

Surface-fragmenting hyperbranched copolymers with hydrolysis-generating zwitterions for antifouling coatings

Surface-fragmenting hyperbranched copolymers with hydrolysis-generating zwitterions have been developed, which exhibit excellent antifouling ability.

Mussel-Inspired Surface Functionalization of PET with Zwitterions and Silver Nanoparticles for the Dual-Enhanced Antifouling and Antibacterial Properties

Herein, we designed and constructed a dual functional surface with antimicrobial and antifouling abilities to prevent protein and bacterial attachment that are significant challenges in biomedical devices. Primary amino-group-capped sulfobetaine of DMMSA was synthesized and then grafted onto polydopamine pretreated PET sheets via click chemistry. The sheets were subsequently immersed into silver ion solution, in which the absorbed silver ions were reduced to silver nanoparticles (AgNPs) in situ by a polydopamine layer. The antifouling assays demonstrated that the resultant PET/DMMSA/AgNPs sheets exhibited great antifouling performances against bovine serum albumin (BSA), bovine fibrinogen (BFG), platelets, and bacteria, the critical proteins/microorganisms leading to implant failure. The antibacterial data suggested that the sheets had dual functions as inhibitors of bacterial growth and bactericide and could efficiently delay the biofilm formation. This repelling and killing approach is green and simple, with potential biomedical applications.

A Facile Way to Prepare Hydrophilic Homogeneous PES Hollow Fiber Membrane via Non-Solvent Assisted Reverse Thermally Induced Phase Separation (RTIPS) Method

Sulfonated polyethersulfone (SPES) was used as an additive to prepare hydrophilic poly(ethersulfone) (PES) hollow fiber membranes via non-solvent assisted reverse thermally induced phase separation (RTIPS) process. The PES/SPES/N,N-dimethylacetamide (DMAc)/ polyethylene glycol 200 (PEG200) casting solutions are lower critical solution temperature (LCST) membrane forming systems. The LCST and phase separation rate increased with the increase of SPES concentrations, while the casting solutions showed shear thinning. When the membrane forming temperature was higher than the LCST, membrane formation mechanism was controlled by non-solvent assisted RTIPS process and the also membranes presented a more porous structure on the surface and a bi-continuous structure on the cross section. The membranes prepared by applying SPES present higher pure water flux than that of the pure PES membrane. The advantages of the SPES additive are reflected by the relatively high flux, good hydrophilicity and excellent mechanical properties at 0.5 wt.% SPES content.

Surface and anti-fouling properties of a polyampholyte hydrogel grafted onto a polyethersulfone membrane

Zwitterion polymers have anti-fouling properties; therefore, grafting new zwitterions to surfaces, particularly as hydrogels, is one of the leading research directions for preventing fouling. Specifically, polyampholytes, polymers of random mixed charged subunits with a net-electric charge, offer a synthetically easy alternative for studying new zwitterions with a broad spectrum of charged moieties. Here, a novel polyampholyte hydrogel was grafted onto the surface of polyethersulfone membrane by copolymerizing a mixture of vinylsulfonic acid (VSA) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METMAC) as the negatively and positively charged monomers, respectively, using various monomer ratios in the polymerization solution, and with N,N'-methylenebisacrylamide as the crosslinker. The physicochemical, morphological and anti-fouling properties of the modified membranes were systematically investigated. Hydrophilic hydrogels were successfully grafted using monomers at different molar ratios. A thin-film zwitterion hydrogel (∼90 nm) was achieved at a 3:1 [VSA:METMAC] molar ratio in the polymerization solution. Among all examined membranes, the zwitterion polyampholyte-modified membrane demonstrated the lowest adsorption of proteins, humic acid, and sodium alginate. It also had low fouling and high flux recovery following filtration with a protein or with an extracellular polymeric substance solution. These findings suggest that this polyampholyte hydrogel is applicable as a low fouling surface coating.