Engineering amphiphilic membrane surfaces based on PEO and PDMS segments for improved antifouling performances

Surface Segregation Methods toward Molecular Separation Membranes

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

Dual functionalized brush copolymers as versatile antifouling coatings

Polymer coatings containing both fouling-resistant and fouling-release components have been reported to show synergistic antifouling properties. However, it remains unclear how the polymer composition influences the antifouling performance, particularly regarding foulants of different sizes and biological natures. Herein, we prepare dual functionalized brush copolymers containing fouling-resistant poly(ethylene glycol) (PEG) and fouling-release polydimethylsiloxane (PDMS) and examine their antifouling performances against different biofoulants. We utilize poly(pentafluorophenyl acrylate) (PPFPA) as a reactive precursor polymer and graft amine-functionalized PEG and PDMS side chains to create PPFPA-g-PEG-g-PDMS brush copolymers of systematically varying compositions. The copolymer films spin-coated on silicon wafers exhibit surface heterogeneity that can be correlated well with the bulk composition of the copolymer. When the copolymer-coated surfaces are examined against protein (human serum albumin and bovine serum albumin) adsorption and cell (lung cancer cells and microalgae) adhesion, they are found to perform better than the homopolymers. The enhanced antifouling properties are attributed to the copolymers having a PEG-rich top layer and a PEG/PDMS mixed bottom layer that work synergistically to resist biofoulant attachment. Furthermore, the composition of the best-performing copolymer is different for different foulants, with PPFPA-g-PEG₃₉-g-PDMS₄₆ exhibiting the best antifouling properties against proteins and PPFPA-g-PEG₅₄-g-PDMS₃₀ exhibiting the best antifouling properties against cells. We explain this difference by considering the changes in the length scale of the surface heterogeneity in relation to the foulant sizes.

Special Issue: Advances in Engineered Nanostructured Antibacterial Surfaces and Coatings

Pathogenic biofilm formation is a major issue of concern in various sectors such as healthcare and medicine, food safety and the food industry, wastewater treatment and drinking water distribution systems, and marine biofouling [...]

Fabrication of a Modified Polyethersulfone Membrane with Anti-Fouling and Self-Cleaning Properties from SiO2-g-PHEMA NPs for Application in Oil/Water Separation

To prepare anti-fouling and self-cleaning membrane material, a physical blending modification combined with surface grafting modification has been carried out; first, poly (2-hydroxyethyl methacrylate) grafted silica nanoparticles (SiO₂-g-PHEMA NPs) were synthesized using surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and used as a blending modifier to fabricate a polyethersulfone (PES)/SiO₂-g-PHEMA organic-inorganic membrane by the phase-inversion method. During the membrane formation process, hydrophobic PES segments coagulated immediately to form a membrane matrix, and the hydrophilic SiO₂-g-PHEMA NPs migrated spontaneously to the membrane surface in order to reduce interfacial energy, which enhanced the hydrophilicity and anti-fouling properties of the PES/SiO₂-g-PHEMA membrane. Importantly, the membrane surface contained abundant PHEMA segments, which provided active sites for further surface functionalization. Subsequently, the carboxyl-terminated fluorocarbon surfactant (fPEG-COOH) composed of hydrophilic polyethyleneglycol segments and low-surface-energy perfluorinated alkyl segments was synthesized via the esterification of fPEG with succinic anhydride. Lastly, the PES/SiO₂-g-PHEMA/fPEG membrane was prepared by grafting fPEG-COOH onto surface of the PES/SiO₂-g-PHEMA. Thus, a versatile membrane surface with both fouling-resistant and fouling-release properties was acquired. The PES/SiO₂-g-PHEMA/fPEG membrane has a large oil-water flux (239.93 L·m^-2·h^-1), almost 21 times that of PES blank membrane and 2.8 times of the PES/SiO₂-g-PHEMA membrane. Compared with the unmodified PES membrane, the flux recovery ratio increased from 45.75% to 90.52%, while the total flux decline ratio decreased drastically from 82.70% to 13.79%, exhibiting outstanding anti-fouling and self-cleaning properties. Moreover, the grafted fPEG segments on the membrane surface show excellent stability due to the presence of stable chemical bonds. The grafted segments remain at the surface of the membrane even after a long shaking treatment. This suggests that this PES/SiO₂-g-PHEMA/fPEG membrane material has potential for application in oil/water separation.

Strong Surface Hydration and Salt Resistant Mechanism of a New Nonfouling Zwitterionic Polymer Based on Protein Stabilizer TMAO

Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O^- in pTMAO and water, and weaker interaction between O^- and metal cations due to the strong repulsion from the N⁺ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.

Mixed-charge pseudo-zwitterionic copolymer brush as broad spectrum antibiofilm coating

Zwitterionic polymers are classical antifouling polymers but they require specialized monomers that have cationic and anionic charges integrated into a single monomer. Herein, we show that pseudo-zwitterionic copolymers synthesized from a mixture of 2 monomers each having a single opposite polarity has excellent antibiofilm efficacy. We have discovered a new mixed-charge copolymer brush (#1-A) synthesized from 2 oppositely charged monomers, the anionic SPM (3-Sulfopropyl methacrylate) and the cationic AMPTMA ((3-Acrylamidopropyl) trimethylammonium chloride), that achieves broad spectrum in vitro antibiofilm effect of greater than 99% reductions against all six Gram-positive and Gram-negative bacteria tested. In the murine subcutaneous wound catheter infection models, the #1-A has good long-term anti-biofilm efficacy against MRSA and Pseudomonas aeruginosa of 3.41 and 3.19 orders respectively, outperforming previous mixed-charge copolymer coatings. We discovered a new method to choose the cationic/anionic pair combination to form the best antibiofilm copolymer brush coating by exploiting the solution polymerization kinetics disparity between the cationic and anionic monomers. We also showed that #1-A is softer and has higher hydration than the classical zwitterionic polymer. This study shows the possibility of achieving potent antibiofilm efficacy by combining readily available opposite singly charged monomers.

Synthesis and Characterization of Dendritic and Linear Glycol Methacrylates and Their Performance as Marine Antifouling Coatings

Dendritic polyglycerol (PG) was covalently coupled to 2-hydroxyethyl methacrylate (HEMA) by an anionically catalyzed ring-opening polymerization generating a dendritic PG-HEMA with four PG repetition units (PG₄MA). Coatings of the methacrylate monomer were prepared by grafting-through and compared against commercially available hydrophilic monomers of HEMA, poly(ethylene) glycol methacrylate (PEGMA), and poly(propylene) glycol methacrylate (PPGMA). The obtained coatings were characterized by modern surface analytical techniques, including water contact angle goniometry (sessile and captive bubble), attenuated total internal reflection Fourier transform infrared spectroscopy, and atomic force microscopy. The antifouling (AF) and fouling-release (FR) properties of the coatings were tested against the model organisms Cobetia marina and Navicula perminuta in laboratory-scale dynamic accumulation assays as well as in a dynamic short-term field exposure (DSFE) in the marine environment. In addition, the hydration of the coatings and their susceptibility toward silt uptake were evaluated, revealing a strong correlation between water uptake, silt incorporation, and field assay performance. While all glycol derivatives showed good resistance in laboratory settlement experiments, PPGMA turned out to be less susceptible to silt incorporation and outperformed PEGMA and PG₄MA in the DSFE assay.

Next-Generation Ultrafiltration Membranes Enabled by Block Polymers

Reliable and equitable access to safe drinking water is a major and growing challenge worldwide. Membrane separations represent one of the most promising strategies for the energy-efficient purification of potential water sources. In particular, porous membranes are used for the ultrafiltration (UF) of water to remove contaminants with nanometric sizes. However, despite exhibiting excellent water permeability and solution processability, existing UF membranes contain a broad distribution of pore sizes that limit their size selectivity. To maximize the potential utility of UF membranes and allow for precise separations, improvements in the size selectivity of these systems must be achieved. Block polymers represent a potentially transformative solution, as these materials self-assemble into well-defined domains of uniform size. Several different strategies have been reported for integrating block polymers into UF membranes, and each strategy has its own set of materials and processing considerations to ensure that uniform and continuous pores are generated. This Review aims to summarize and critically analyze the chemistries, processing techniques, and properties required for the most common methods for producing porous membranes from block polymers, with a particular focus on the fundamental mechanisms underlying block polymer self-assembly and pore formation. Critical structure-property-performance metrics will be analyzed for block polymer UF membranes to understand how these membranes compare to commercial UF membranes and to identify key research areas for continued improvements. This Review is intended to inform readers of the capabilities and current challenges of block polymer UF membranes, while stimulating critical thought on strategies to advance these technologies.

Grafting Activated Graphene Oxide Nanosheets onto Ultrafiltration Membranes Using Polydopamine to Enhance Antifouling Properties

Graphene oxide (GO) nanosheets are negatively charged and exhibit excellent antifouling properties. However, their hydrophilicity makes it challenging for their grafting onto membrane surfaces to improve antifouling properties for long-term underwater operation. Herein, we demonstrate a versatile approach to covalently graft GO onto ultrafiltration membrane surfaces in aqueous solutions at ≈22 °C. The membrane surface is first primed using dopamine and then reacted with activated GO (aGO) containing amine-reactive esters. The aGO grafting improves the membrane surface hydrophilicity without decreasing water permeance. When the membranes are challenged with 1.0 g/L sodium alginate in a constant-flux crossflow system, the aGO grafting increases the critical flux by 20% and reduces the fouling rate by 63% compared with the pristine membrane. The modified membranes demonstrate stability for 48 h operation and interval cleanings using NaOH solutions.

Sharpening Nanofiltration: Strategies for Enhanced Membrane Selectivity

Nanofiltration plays an increasingly large role in many industrial applications, such as water treatment (e.g., desalination, water softening, and fluoride removal) and resource recovery (e.g., alkaline earth metals). Energy consumption and benefits of nanofiltration processes are directly determined by the selectivity of the nanofiltration membranes, which is largely governed by pore-size distribution and Donnan effects. During operation, the separation performance of unmodified nanofiltration membranes will also be impacted (deleteriously) upon unavoidable membrane fouling. Many efforts, therefore, have been directed toward enhancing the selectivity of nanofiltration membranes, which can be classified into membrane fabrication method improvement and process intensification. This review summarizes recent developments in the field and provides guidance for potential future approaches to improve the selectivity of nanofiltration membranes.

Recent Advances in Surface Nanoengineering for Biofilm Prevention and Control. Part I: Molecular Basis of Biofilm Recalcitrance. Passive Anti-Biofouling Nanocoatings

Medical device-associated infections are becoming a leading cause of morbidity and mortality worldwide, prompting researchers to find new, more effective ways to control the bacterial colonisation of surfaces and biofilm development. Bacteria in biofilms exhibit a set of "emergent properties", meaning those properties that are not predictable from the study of free-living bacterial cells. The social coordinated behaviour in the biofilm lifestyle involves intricate signaling pathways and molecular mechanisms underlying the gain in resistance and tolerance (recalcitrance) towards antimicrobial agents as compared to free-floating bacteria. Nanotechnology provides powerful tools to disrupt the processes responsible for recalcitrance development in all stages of the biofilm life cycle. The present paper is a state-of-the-art review of the surface nanoengineering strategies currently used to design antibiofilm coatings. The review is structurally organised in two parts according to the targeted biofilm life cycle stages and molecular mechanisms intervening in recalcitrance development. Therefore, in the present first part, we begin with a presentation of the current knowledge of the molecular mechanisms responsible for increased recalcitrance that have to be disrupted. Further, we deal with passive surface nanoengineering strategies that aim to prevent bacterial cells from settling onto a biotic or abiotic surface. Both "fouling-resistant" and "fouling release" strategies are addressed as well as their synergic combination in a single unique nanoplatform.

Grafting polysiloxane onto ultrafiltration membranes to optimize surface energy and mitigate fouling

Conventional approaches to mitigate fouling of membrane surfaces impart hydrophilicity to the membrane surface, which increases the water of hydration and fluidity near the surface. By contrast, we demonstrate here that tuning the membrane surface energy close to that of the dispersive component of water surface tension (21.8 mN m^-1) can also improve the antifouling properties of the membrane. Specifically, ultrafiltration (UF) membranes were first modified using polydopamine (PDA) followed by grafting of amine-terminated polysiloxane (PSi-NH₂). For example, with 2 g L^-1 PSi-NH₂ coating solution, the obtained coating layer contains 53% by mass fraction PSi-NH₂ and exhibits a total surface energy of 21 mN m^-1, decreasing the adsorption of bovine serum albumin by 44% compared to the unmodified membrane. When challenged with 1 g L^-1 sodium alginate in a constant-flux crossflow system, the PSi-NH₂-grafted membrane exhibits a 70% lower fouling rate than the pristine membrane at a water flux of 110 L (m² h)^-1 and good stability when cleaned with NaOH solutions.

Omni-Directional Protected Nanofiber Membranes by Surface Segregation of PDMS-Terminated Triblock Copolymer for High-Efficiency Oil/Water Emulsion Separation

An excellent antifouling membrane with high permeate flux is required for oil/water emulsion separation due to ever-increasing oily industrial wastewater. Thus, an intriguing integration of the Omni-directional protected porous membrane that combines a high porosity nanofiber membrane with a surface segregation mechanism is established for the first time. By applying polydimethylsiloxane(PDMS)-terminated triblock copolymer, the enrichment of the hydrophilic poly(ethylene oxide) (PEO) segment and the nonpolar PDMS segment on the surface of the nanofiber endowed the nanofiber membrane with underwater oleophobicity and low oil adhesion force, exhibiting oil resistance as well as oil release property. An ultrahigh permeate flux of ∼7115 L m^-2 h^-1 with a separation efficiency of ∼97.88% is achieved under the driving force of gravity (∼0.9 kPa), which is the highest permeate flux ever reported under similar conditions. Moreover, the surface segregation nanofiber membrane shows excellent reusability and ultrahigh permeate flux with the assistance of stirring in a long-term test, revealing the promising performances for the further particular application of oily wastewater.

Strong Hydration at the Poly(ethylene glycol) Brush/Albumin Solution Interface

Albumin molecules are extensively used as biocompatible coatings, and poly(ethylene glycol) (PEG) materials are widely used for antifouling. PEG materials have excellent antifouling property because of their strong surface hydration. Our previous research indicates that hydration at the PEG/bovine serum albumin solution interface is stronger than that at the PEG/water interface. This research shows that this observation is general for different types of albumin molecules. Different albumins including bovine, porcine, rat, rabbit, and sheep serum albumins were studied in this research. It was found that the hydration at the PEG methacrylate (pOEGMA)/albumin solution interface is always stronger than that at the pOEGMA/water interface. Here, we define "strong interfacial hydration" as "ordered strongly hydrogen-bonded interfacial water". We believe that such a strong hydration is because of the strong hydration on the albumin surface, leading to its biocompatible property. All of the albumin molecules demonstrated stronger hydration on the pOEGMA surface compared to other protein molecules such as lysozyme and fibrinogen. The strong hydration on albumin molecules is related to the high surface coverage of glutamic acid and lysine with similar amounts.

Solvent-driven migration of highly polar monomers into hydrophobic PDMS produces a thick graft layer via subsurface initiated ATRP for efficient antibiofouling

Organic solvents that possess affinity towards both polar monomers and hydrophobic PDMS play a “driving” role in the diffusion of polar monomers into the subsurface of the PDMS substrate.

Surface-Modifying Polymers for Blood-Contacting Polymeric Biomaterials

Bulk blending is considered as one of the most effective and straightforward ways to improve the hemo-compatibility of blood-contacting polymeric biomaterials among many surface modification methods. Zwitterionic structure-, glycocalyx-like structure-, and heparin-like structure-based oligomers have been synthesized as additives and blended with base polymers to improve the blood compatibility of base polymers. Fluorinated end- and side-functionalized oligomers could promote the migration of functionalized groups to the surface of biomedical polymers without changing their bulk properties, and it highly depends on the number and concentration of functional groups. Moreover, oligomers having both zwitterion and fluorine are receiving considerable attention due to their desirable phase separation, which can avoid undesired protein adsorption and platelet adhesion. The surface analysis of the surface-modified materials is usually investigated by analytical tools such as contact angle measurement, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Blood compatibility is mainly evaluated via platelet adhesion and protein adsorption test, and the result showed a significant decrease in the amount of undesirable adsorption. These analyses indicated that surface modification using bulk blending technique effectively improves blood compatibility of polymeric biomaterials.

Improving the Performance of PVDF/PVDF-g-PEGMA Ultrafiltration Membranes by Partial Solvent Substitution with Green Solvent Dimethyl Sulfoxide during Fabrication

Traditional organic solvents used in membrane manufacturing, such as dimethylformamide and tetrahydrofuran, are generally very hazardous and harmful to the environment and human health. Their total or partial substitution with green solvent dimethyl sulfoxide (DMSO) is proposed to fabricate membranes composed of poly(vinylidene fluoride) (PVDF) blended with PVDF-graft-poly(ethylene glycol) methyl ether methacrylate (PEGMA), with the purpose to accomplish a greener chemical process and enhance the membrane performance. Various organic solvent compositions were first investigated using the Hansen solubility theory, and the best mixture was thus applied experimentally. The membrane prepared by a ratio of N,N-dimethylacetamide/DMSO = 7:3 outperformed the membranes prepared by other solvent mixtures. This membrane showed high wetting behavior with the water contact angle declining from 71 to 7° in 18 s and a pure water flux reaching values larger than 700 L m^-2 h^-1 under 0.07 MPa applied hydraulic pressure. The membrane rejected sodium alginate at a rate of 87%, and nearly complete flux recovery was achieved following fouling and physical cleaning. The introduction of green chemistry concepts to PVDF/PVDF-g-PEGMA blended membranes is a step forward in the goal to increase the sustainability of membrane production.

Amphiphilic Block Copolymer of Poly(dimethylsiloxane) and Methoxypolyethylene Glycols for High-Permeable Polysulfone Membrane Preparation

Poly(dimethylsiloxane)-block-methoxypolyethylene glycols (PDMS-b-mPEG) were synthesized by Steglich esterification. The high-permeable membrane (PSf/PDMS-b-mPEG) was prepared by using PDMS-b-mPEG as additives. The successful synthesis of PDMS-b-mPEG was confirmed by nuclear magnetic resonance. Field emission scanning electron microscopy images show that the distribution of finger-like macroporous and sponge-like macroporous can be modulated by controlling the ratio of the hydrophilic/hydrophobic components of additives. The distribution of additives and membrane wettability are validated with X-ray photoelectron spectroscopy and water contact angle test. The permeability of the blended membrane, especially for the membrane PSf/PDMS-b-mPEG1900 (M3), was remarkably improved. The water permeability of M3 (239.4 L/m²·h·bar) was 6.6 times that of the unblended membrane M0 (42.5 L/m²·h·bar). The findings of protein BSA filtration show that the flux recovery ratio of M3 is 89.2% at a BSA retention rate of about 80%, which demonstrates that the polysulfone membranes blended with PDMS-b-mPEG have excellent antifouling performance and extraordinary permeability.

Target capturing performance of microfluidic channel surface immobilized aptamers: the effects of spacer lengths

Aptamers have been widely used to recognize and capture their targets in sensitive detection applications, such as in detections of circulating tumor cells. In this study, we investigate the effects of different lengths of oligo-T spacers on surface tethered sgc8 aptamers and their target capturing performances. To achieve this, sgc8 aptamers were immobilized onto microfluidic channel surfaces via oligo-T spacers of different lengths, and the target capturing performances of these immobilized aptamers were studied using CCRF-CEM cells. We demonstrate that the capturing performances of the immobilized aptamers were significantly affected by steric hindrance. Our results also show that aptamers immobilized on surfaces via spacers of ten Ts demonstrated the best cell capturing performances; aptamers with either too short or too long oligo-T spacers showed reduced cell capturing performances. Therefore it can be concluded that spacer optimizations are critically important for surface tethered aptamers that are commonly used in microfluidic devices for sensitive target sensing and detections.

Enhanced permeability and fouling-resistant capacity of poly(vinylidene fluoride) ultrafiltration membrane based on the PPG-co-PEG-co-PPG copolymer with two hydrophobic terminals and one hydrophilic intermediate

A simple and efficient route was used to prepare an amphiphilic copolymer (poly(propylene glycol)-co-poly(ethylene glycol)-co-poly(propylene glycol)) (PPG-co-PEG-co-PPG) by one-pot polymerization reaction. This copolymer was used as the hydrophilic additive in preparation of poly(vinylidene fluoride) (PVDF) ultrafiltration membranes via immersion-precipitation process. Surface characteristics of the membranes were confirmed by contact angle measurements, zeta potential, attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. During filtration experiments, the modified membranes showed better permeation and antifouling performances compared to PVDF membranes with bovine serum albumin, sodium alginate and yeast. After hydraulic stirring cleaning with deionized water, water flux recovery and rejection ratio of the modified membranes were higher than those of pristine PVDF membrane, and the flux recovery ratio was maximized at 94.29%. It was suggested that PPG-co-PEG-co-PPG copolymer was anchored in the PVDF membrane through the two hydrophobic ends of PPG blocks, while the hydrophilic intermediate of the PEG block segregated onto the membrane or pore surface during the membrane preparation process. The synthesized method of amphiphilic PPG-co-PEG-co-PPG copolymer paved a novel way to solve the problems of less compatibility between the copolymer and membrane matrix and instability with water molecules in the ultrafiltration process.

Capillary effect in Janus electrospun nanofiber membrane for oil/water emulsion separation

Janus electrospun nanofiber membranes (J-ENMs) have attracted considerable interest as membranes for oil-in-water emulsion separation due to the opposite properties on each side of the membrane. Such properties can provide capillary effect and achieve water unidirectional transportation. However, the capillary effect on performances of the J-ENMs is still obscure. Therefore, it is highly important to investigate the relation of pore size, capillary pressure, and fluid flux of them. For this study, J-ENMs, which have a dual-layer structure with hydrophilic polyacrylonitrile (PAN) and hydrophobic polystyrene (PS) nanofibrous membranes simultaneously, were fabricated via the electrospinning process. Among the fabricated membranes, the large pore sizes of the PS layer of J-ENMs affected capillary pressure leading to a pure water flux increase of nine times that of the small pore size. For emulsion flux, oil droplets can pass through a large pore of the PS layer easily and can cause a decrease in emulsion flux. Nevertheless, the emulsion flux of J-ENMs was 1.7 times higher than that of single layer membrane, which showed a promising application for the oil/water separation field.

Graphitic carbon nitride (g-C3N4) nanosheets functionalized composite membrane with self-cleaning and antibacterial performance

Membrane fouling significantly impedes membrane performance and thus short lifespan of the membrane. Membranes that functionalized with photocatalytic activity are deemed as an effective and novel approach to settle membrane fouling. The membranes with self-cleaning and antibacterial performance were fabricated via facilely filtering g-C₃N₄ nanosheets onto polyacrylonitrile (PAN) porous substrates. The g-C₃N₄ nanosheets were exfoliated by acid etching and ultrasound treatment, and the exfoliated nanosheets was verified by Fourier transform infrared spectra, Atomic force microscopy and X-ray diffraction. The g-C₃N₄ nanosheets functionalized composite membranes have a water permeability of 11.70 L m^-2 h^-1 bar^-1 and a good antibacterial activity. In addition, the membranes could be restored their original permeability and their surfaces were close to initial color even after three cycles rejecting dyes and post treatment under irradiation with visible light. Besides, the degradable and antimicrobial mechanisms of the membranes were investigated respectively. These g-C3N4 nanosheets composite membranes with self-cleaning and antimicrobial properties have a potential feasibility in water treatment, and provide an alternative method for fabricating self-cleaning membranes.

Aptamer surface functionalization of microfluidic devices using dendrimers as multi-handled templates and its application in sensitive detections of foodborne pathogenic bacteria

A microfluidic system that incorporates both dendrimers and aptamers to detect E. coli O157:H7 is developed. To achieve this, generation 7-polyamidoamine dendrimers were immobilized onto the detection surfaces of PDMS microfluidic channels; subsequently aptamers against E. coli O157:H7 were conjugated onto the microchannel surfaces via the immobilized dendrimers as templates. Surface modifications were characterized by FTIR, XPS, water contact angles, fluorescence microscopy and AFM to confirm the success of each surface modification steps. The efficacy of this simple microchannel in detection was investigated using E. coli O157:H7 spiked samples. Our results showed that this interesting approach significantly increased the amount of aptamers available on the microfluidic channel surfaces to capture E. coli O157:H7 cells to allow sensitive detection, which in turn resulted in detections of E. coli O157:H7 cells at a low limit of detection of 10² cells mL^-1. The results also demonstrated that in comparison with the generation 4-polyamidoamine dendrimers (G4) modified microchannels, those modified with G7 showed enhanced detection signals, improved target capturing efficiencies, and at higher throughput. This simple whole cell detection design has not been reported in the literature and it is an interesting and effective approach to developing a sensitive and rapid detection platform for foodborne pathogenic bacteria.

Effect of volatile solvent and evaporation time on formation and performance of PVC/PVC-g-PEGMA blended membranes

The synthesis process of the PVC/PVC-g-PEGMA membranes.

A novel poly(arylene ether nitrile) ultrafiltration membrane for water purification and its antifouling property with in situ-generated SiO2 nanoparticles

In this work, poly(arylene ether nitrile) (PEN) was utilized to fabricate a separation membrane to remove dye molecules and oil/water emulsions for the very first time. Specifically, 15 wt% polyethylene glycol ([Formula: see text] = 800 Da) was added to the casting solution as a pore-forming agent to enhance the flux. In situ-generated SiO2 nanoparticles (NPs) were utilized to improve the membrane surface hydrophilicity by the hydrolyzation of tetraethyl orthosilicate under weak acid conditions. However, the surface hydrophilicity improvement was not significant. It may be because the strong mechanical strength of PEN caused most of the SiO2 NPs to be buried within the polymer matrix or SiO2 NPs were lost by dissolution in the acidic water bath. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were performed to study the membrane surface chemical features. Scanning electron microscopy images were obtained to observe the membrane cross-section morphology.

Development and Characterization of Mechanically Durable Silicone-Polythiourethane Composites Modified with Tetrapodal Shaped ZnO Particles for the Potential Application as Fouling-Release Coating in the Marine Sector

Ecological considerations strongly necessitate the development of environmentally friendly antifouling paints. A promising alternative to biocide containing antifouling paints are fouling-release coatings, which are non-toxic and designed to prevent permanent attachment of marine organisms to the surface, due to their low surface energy. However, these coatings suffer from insufficient mechanical properties, which make them unsuitable for mechanically stressed surfaces e.g., on ship hulls. To overcome those obstacles, polydimethylsiloxane (PDMS)-polythiourethane (PTU) composites modified with tetrapodal shaped micro-nano ZnO particles (t-ZnO) were produced and characterized by evaluating the surface energy, mechanical properties, and fouling-release performance. Among all variations, PTU/1 wt.% PDMS composites with 1 wt.% t-ZnO particles possess superior properties for applications as fouling-release coatings for maritime purposes.

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers

Interfacial water structure on a polymer surface in water (or surface hydration) is related to the antifouling activity of the polymer. Zwitterionic polymer materials exhibit excellent antifouling activity due to their strong surface hydration. It was proposed to replace zwitterionic polymers using mixed charged polymers because it is much easier to prepare mixed charged polymer samples with much lower costs. In this study, using sum frequency generation (SFG) vibrational spectroscopy, we investigated interfacial water structures on mixed charged polymer surfaces in water and how such structures change while being exposed to salt solutions and protein solutions. The 1:1 mixed charged polymer exhibits excellent antifouling property whereas other mixed charged polymers with different ratios of the positive/negative charges do not. It was found that on the 1:1 mixed charged polymer surface, SFG water signal is dominated by the contribution of the strongly hydrogen bonded water molecules, indicating strong hydration of the polymer surface. The responses of the 1:1 mixed charged polymer surface to salt solutions are similar to those of zwitterionic polymers. Interestingly, exposure to high concentrations of salt solutions leads to stronger hydration of the 1:1 mixed charged polymer surface after replacing the salt solution with water. Protein molecules do not substantially perturb the interfacial water structure on the 1:1 mixed charged polymer surface and do not adsorb to the surface, showing that this mixed charged polymer is an excellent antifouling material.