Antifouling thin-film composite membranes with multi-defense properties by controllably constructing amphiphilic diblock copolymer brush layer

Photo-responsive anti-fouling polyzwitterionic brushes: a mesoscopic simulation

The antifouling effects of a toothbrush-shaped photo-responsive polyzwitterionic membrane were studied via dissipative particle dynamics simulations in this work. The results reveal that the membrane modified by spiropyran methacrylate brushes displays photo-switchable and antifouling capability due to the photo-induced ring-opening reaction. Namely, surface morphology and hydrophilicity change in response to visible or UV light irradiation, which can be observed visually by protein adsorption and desorption. Further study indicates that: (1) brush-modification density can influence the structure and properties of the membrane. With low modification density, systems cannot establish an intact selective layer, which hinders the antifouling ability; as the modification density increases, the intact selective layer can be formed, which is conducive to the expression of photo-responsiveness and antifouling capability. (2) Factors of toothbrush-hair length and grafting ratio can influence the establishment of a light-responsive surface: as the grafting ratio and toothbrush-hair length increase, the light-responsive surface is gradually formed, meanwhile, the antifouling ability can be continuously reinforced under UV light irradiation. (3) As the brushes switch into a zwitterionic merocyanine state under UV exposure, the selective layer swelling becomes stronger than that with a hydrophobic spiropyran state under visible exposure. This is owing to the enhanced interaction between zwitterionic brushes and water, which is the root of the antifouling effect. The present work is expected to provide some guidelines for the design and development of novel antifouling membrane surfaces.

Formation of Amphiphilic Zwitterionic Thin Poly(SBMA-co-TFEMA) Brushes on Solid Surfaces for Marine Antifouling Applications

Water molecules can bind to zwitterionic polymers, such as carboxybetaine and sulfobetaine, forming strong hydration layers along the polymer chains. Such hydration layers act as a barrier to impede the attachment of marine fouling organisms; therefore, zwitterionic polymer coatings have been of considerable interest as marine antifouling coatings. However, recent studies have shown that severe adsorption of marine sediments occurs on zwitterionic-polymer-coated surfaces, resulting in the degradation of their marine antifouling performance. Therefore, a novel approach for forming amphiphilic zwitterionic polymers using zwitterionic and hydrophobic monomers is being investigated to simultaneously inhibit both sediment adsorption and marine fouling. In this study, amphiphilic zwitterionic thin polymer brushes composed of sulfobetaine methacrylate (SBMA) and trifluoroethyl methacrylate (TFEMA) were synthesized on Si/SiO2 surfaces via surface-initiated atom transfer radical polymerization. For this, a facile metal-ion-mediated method was developed for immobilizing polymerization initiators on solid substrates to subsequently form poly(SBMA-co-TFEMA) brushes on the initiator-coated substrate surface. Poly(SBMA-co-TFEMA) brushes with various SBMA/TFEMA ratios were prepared to determine the composition at which both marine diatom adhesion and sediment adsorption can be prevented effectively. The results indicate that poly(SBMA-co-TFEMA) brushes prepared with an SBMA/TFEMA ratio of 3:7 effectively inhibit both sediment adsorption and marine diatom adhesion, thereby exhibiting balanced marine antifouling properties. Thus, the findings of this study provide important insights into the design of amphiphilic marine antifouling materials.

Flexible, durable, and anti-fouling maghemite copper oxide nanocomposite-based membrane with ultra-high flux and efficiency for oil-in-water emulsions separation

In this study, we developed a novel nanocomposite-based membrane using maghemite copper oxide (MC) to enhance the separation efficiency of poly(vinyl chloride) (PVC) membranes for oil-in-water emulsions. The MC nanocomposite was synthesized using a co-precipitation method and incorporated into a PVC matrix by casting. The resulting nanocomposite-based membrane demonstrated a high degree of crystallinity and well-dispersed nanostructure, as confirmed by TEM, SEM, XRD, and FT-IR analyses. The performance of the membrane was evaluated in terms of water flux, solute rejection, and anti-fouling properties. The pinnacle of performance was unequivocally reached with a solution dosage of 50 mL, a solution concentration of 100 mg L-1, and a pump pressure of 2 bar, ensuring that every facet of the membrane's potential was fully harnessed. The new fabricated membrane exhibited superior efficiency for oil-water separation, with a rejection rate of 98% and an ultra-high flux of 0.102 L/m2 h compared to pure PVC membranes with about 90% rejection rate and an ultra-high flux of 0.085 L/m2 h. Furthermore, meticulous contact angle measurements revealed that the PMC nanocomposite membrane exhibited markedly lower contact angles (65° with water, 50° with ethanol, and 25° with hexane) compared to PVC membranes. This substantial reduction, transitioning from 85 to 65° with water, 65 to 50° with ethanol, and 45 to 25° with hexane for pure PVC membranes, underscores the profound enhancement in hydrophilicity attributed to the heightened nanoparticle content. Importantly, the rejection efficiency remained stable over five cycles, indicating excellent anti-fouling and cycling stability. The results highlight the potential of the maghemite copper oxide nanocomposite-based PVC membrane as a promising material for effective oil-in-water emulsion separation. This development opens up new possibilities for more flexible, durable, and anti-fouling membranes, making them ideal candidates for potential applications in separation technology. The presented findings provide valuable information for the advancement of membrane technology and its utilization in various industries, addressing the pressing challenge of oil-induced water pollution and promoting environmental sustainability.

Measurement of the Adhesion Force of a Living Sessile Organism on Antifouling Coating Surfaces Prepared with Polysulfobetaine-Grafted Particles

An antifouling polymer brush-like structure was fabricated by a simple and versatile dip-coating method of sulfobetaine containing copolymer-grafted silica nanoparticles (SiNPs) and alkyl diiodide cross-linkers. Surface-initiated atom transfer radical copolymerization of 3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate (MAPS) and N,N-dimethylaminoethyl methacrylate (DMAEMA) was carried out from initiator-immobilized SiNPs to give poly(MAPS-co-DMAEMA)-grafted SiNPs (MAPS/DMAEMA = 9/1, mol/mol) with diameters of 150-170 nm. The SiNP-g-copolymer/2,2,2-trifluoroethanol solution was dip-coated on silicon and glass substrates. Successive treatment with 1,4-diiodobutane in methanol gave a hydrophilic cross-linked coating film for the SiNP-g-copolymer. The cross-linked particle brushes did not peel off from the substrate even after washing with water in an ultrasonic cleaner despite the simple physical absorption of the SiNP-g-copolymer on the substrate surface. The adhesion force of the tentacle of a living barnacle cyprid on a glass surface covered with the cross-linked SiNP-g-copolymer was directly measured by scanning probe microscopy in seawater. The coating film exhibited extremely low adhesion to the cypris larva in the seawater, expecting this to be an effective antifouling property.

Anchoring of Polymer Loops on Enzyme-Immobilized Mesoporous ZIF-8 Enhances the Recognition Selectivity of Angiotensin-Converting Enzyme Inhibitory Peptides

Immobilized angiotensin-converting enzyme (ACE) is a promising material for the rapid screening of antihypertensive drugs, but the nonspecific adsorption is a serious problem in separation processes involving complex biological products. In this study, triblock copolymers with dopamine (DA) block as anchors and PEG block as the main body (DA-PEGx-DA) were attached to an immobilized ACE (ACE@mZIF-8/PDA, AmZP) surface via the “grafting to” strategy which endowed them with anti-nonspecific adsorption. The influence of DA-PEGx-DA chain length on nonspecific adsorption was confirmed. The excellent specificity and reusability of the obtained ACE@mZIF-8/PDA/DA-PEG5000-DA (AmZPP5000) was validated by screening two known ACE inhibitory peptides Val-Pro-Pro (VPP, competitive inhibitory peptides of ACE) and Gly-Met-Lys-Cys-Ala-Phe (GF-6, noncompetitive inhibitory peptides of ACE) from a mixture containing active and inactive compounds. These results demonstrate that anchored polymer loops are effective for high-recognition selectivity and AmZPP5000 is a promising compound for the efficient separation of ACE inhibitors in biological samples.

Controlling self-assembling co-polymer coatings of hydrophilic polysaccharide substrates via co-polymer block length ratio

HYPOTHESIS

The degree of polymerization of amphiphilic di-block co-polymers, which can be varied with ease in computer simulations, provides a means to control self-assembling di-block co-polymer coatings on hydrophilic substrates.

SIMULATIONS

We examine self-assembly of linear amphiphilic di-block co-polymers on hydrophilic surface via dissipative particle dynamics simulations. The system models a glucose based polysaccharide surface on which random co-polymers of styrene and n-butyl acrylate, as the hydrophobic block, and starch, as the hydrophilic block, forms a film. Such setups are common in e.g. hygiene, pharmaceutical, and paper product applications.

FINDINGS

Variation of the block length ratio (35 monomers in total) reveals that all examined compositions readily coat the substrate. However, strongly asymmetric block co-polymers with short hydrophobic segments are best in wetting the surface, whereas approximately symmetric composition leads to most stable films with highest internal order and well-defined internal stratification. At intermediate asymmetries, isolated hydrophobic domains form. We map the sensitivity and stability of the assembly response for a large variety of interaction parameters. The reported response persists for a wide polymer mixing interactions range, providing general means to tune surface coating films and their internal structure, including compartmentalization.

Unveiling the impact of imidazole derivative with mechanistic insights into neutralize interfacial polymerized membranes for improved solute-solute selectivity

Domestic wastewater (DWW) contains a reservoir of nutrients, such as nitrogen, potassium, and phosphorus; however, emerging micropollutants (EMPs) hinder its applications in resource recovery. In this study, a novel class of nanofiltration (NF) membranes was developed; it enabled the efficient removal of harmful EMP constituents while preserving valuable nutrients in the permeate. Neutral (IM-N) and positively charged (IM-P) imidazole derivative compounds have been used to chemically functionalize pristine polyamide (PA) membranes to synchronously inhibit the hydrolysis of residual acyl chloride and promote their amination. Owing to their distinct properties, these IM modifiers can custom-build the membrane physicochemical properties and structures to benefit the NF process in DWW treatment. The electroneutral NF membrane exhibited ultrahigh solute-solute selectivity by minimizing the Donnan effects on ion penetration (K, N, and P ions rejection < 25%) while imposing remarkable size-sieving obstruction against EMPs (rejection ratio > 91%). Moreover, the hydrophilic IM-modifier synergistically led to enhanced water permeance of 9.2 L m^-2 h^-1 bar^-1, reaching a 2-fold higher magnitude than that of the pristine PA membrane, along with excellent antifouling/antibacterial fouling properties. This study may provide a paradigm shift in membrane technology to convert wastewater streams into valuable water and nutrient resources.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

In-situ formation of fluorophore cross-linked micellar thick films and usage as drug delivery material for Propranolol HCl

Polyethylene glycol monomethyl ether-block-poly(glycidyl methacrylate)-block-poly[2-(diethylamino)ethyl methacrylate] triblock copolymer was synthesized to prepare self-assembled micron sized films via a novel approach named as "phase separated micellar self assembly method". Liquid-air interface self assembly method via slow solvent evaporation was used to obtain micellar films. Cross-linking of polymer films was carried out by diffusion of fluorophore cross-linker into polymer solution from subphase. In-situ micellar formation was triggered via driven forces such as molecular interactions and slow evaporation of solvent. Thiazolo[5,4-d]thiazole based cross-linker fluorophores containing alkali subphases were used to prepare highly fluorescent cross-linked micellar films. Micellar morphologies of the films were characterized with SEM while the cross-sections of fluorophore cross-linked films were observed with TEM analysis to examine diffusion of the dye as nano-sized particles into the polymer film. Convenience and usability of the micellar films as drug delivery material were demonstrated with Propranolol HCl release via UV-Vis spectroscopic studies. Optical properties of the films before and after drug release were determined via photoluminescence spectroscopy to be able to sense the completion of the drug release process. Swelling and shrinkage properties of the films were also determined in different pH values. These highly fluorescent polymer films have great potential as drug delivery materials and biomedical sensing applications.

Sessile Drop Method: Critical Analysis and Optimization for Measuring the Contact Angle of an Ion-Exchange Membrane Surface

The contact angle between a membrane surface and a waterdrop lying on its surface provides important information about the hydrophilicity/hydrophobicity of the membrane. This method is well-developed for solid non-swelling materials. However, ion-exchange membranes (IEMs) are gel-like solids that swell in liquids. When an IEM is exposed to air, its degree of swelling changes rapidly, making it difficult to measure the contact angle. In this paper, we examine the known experience of measuring contact angles and suggest a simple equipment that allows the membrane to remain swollen during measurements. An optimized protocol makes it possible to obtain reliable and reproducible results. Measuring parameters such as drop size, water dosing speed and others are optimized. Contact angle measurements are shown for a large number of commercial membranes. These data are supplemented with values from other surface characteristics from optical and profilometric measurements.

In Situ Chemical Modification with Zwitterionic Copolymers of Nanofiltration Membranes: Cure for the Trade-Off between Filtration and Antifouling Performance

Breaking the trade-off between filtration performance and antifouling property is critical to enabling a thin-film nanocomposite (TFC) nanofiltration (NF) membrane for a wide range of feed streams. We proposed a novel design route for TFC NF membranes by grafting well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and 2-aminoethyl methacrylate hydrochloride (AEMA) on the polyamide surfaces via an in situ surface chemical modification process. The successful grafting of a zwitterionic copolymer imparted the modified NF membranes with better surface hydrophilicity, a larger actual surface area (i.e., nodular structures), and a thinner polyamide layer. As a result, the water permeability of the modified membrane (i.e., TFC-10) was triple that of the pristine TFC membrane while maintaining high Na₂SO₄ rejection. We further demonstrated that the TFC-10 membrane possessed exceptional antifouling properties in both static adsorption tests and three cycles of dynamic protein and humic acid fouling tests. To recap, this work provides valuable insights and strategies for the fabrication of TFC NF membranes with simultaneously enhanced filtration performance and antifouling property.

Conformation-dominated surface antifouling and aqueous lubrication

Antifouling and aqueous lubrication are important properties for biomaterials, especially for those with implantation purposes. In order to better understand the polymer conformation dependence of the surface antifouling and lubrication properties, poly(ethylene glycol) (PEG) polymers with mono-functional and difunctional catechol anchors were designed and anchored on surface to adopt tail and loop conformations. Diblock and triblock copolymers with poly(dopamine methacrylamide) (PDMA) block as anchors and PEG block as the main body were synthesized and anchored on silicon surfaces by a "grafting to" strategy. The chemical composition, film thickness, and surface roughness of both coatings were controlled to be similar to give a direct comparison of looped brushes and tailed analogues. Then, the antifouling and surface friction behaviors were detected to verify the topological conformation effect of PEG polymer brushes. Results showed that PEG triblock copolymer modified surface exhibited an obviously better antifouling property and a lower friction coefficient of ∼0.011 than that of PEG diblock copolymer modified surface. Additionally, calculation and simulation results demonstrated that triblock copolymer had higher adsorption energy and anchored on surface with looped conformation. It is indicated that the strongly anchored PEG loops are effective for excellent antifouling and lubricating properties due to its strong hydration and steric hindrance. The conformation-dominated enhanced antifouling and reduced interfacial friction is an effective method for the development of excellent antifouling surfaces.

Construction of Enzyme-Responsive Micelles Based on Theranostic Zwitterionic Conjugated Bottlebrush Copolymers with Brush-on-Brush Architecture for Cell Imaging and Anticancer Drug Delivery

Bottlebrush copolymers with different chemical structures and compositions as well as diverse architectures represent an important kind of material for various applications, such as biomedical devices. To our knowledge, zwitterionic conjugated bottlebrush copolymers integrating fluorescence imaging and tumor microenvironment-specific responsiveness for efficient intracellular drug release have been rarely reported, likely because of the lack of an efficient synthetic approach. For this purpose, in this study, we reported the successful preparation of well-defined theranostic zwitterionic bottlebrush copolymers with unique brush-on-brush architecture. Specifically, the bottlebrush copolymers were composed of a fluorescent backbone of polyfluorene derivate (PFONPN) possessing the fluorescence resonance energy transfer with doxorubicin (DOX), primary brushes of poly(2-hydroxyethyl methacrylate) (PHEMA), and secondary graft brushes of an enzyme-degradable polytyrosine (PTyr) block as well as a zwitterionic poly(oligo (ethylene glycol) monomethyl ether methacrylate-co-sulfobetaine methacrylate) (P(OEGMA-co-SBMA)) chain with super hydrophilicity and highly antifouling ability via elegant integration of Suzuki coupling, NCA ROP and ATRP techniques. Notably, the resulting bottlebrush copolymer, PFONPN9-g-(PHEMA15-g-(PTyr16-b-P(OEGMA6-co-SBMA6)2)) (P2) with a lower MW ratio of the hydrophobic side chains of PTyr and hydrophilic side chains of P(OEGMA-co-SBMA) could self-assemble into stabilized unimolecular micelles in an aqueous phase. The resulting unimolecular micelles showed a fluorescence quantum yield of 3.9% that is mainly affected by the pendant phenol groups of PTyr side chains and a drug-loading content (DLC) of approximately 15.4% and entrapment efficiency (EE) of 90.6% for DOX, higher than the other micelle analogs, because of the efficient supramolecular interactions of π–π stacking between the PTyr blocks and drug molecules, as well as the moderate hydrophilic chain length. The fluorescence of the PFONPN backbone enables fluorescence resonance energy transfer (FRET) with DOX and visualization of intracellular trafficking of the theranostic micelles. Most importantly, the drug-loaded micelles showed accelerated drug release in the presence of proteinase K because of the enzyme-triggered degradation of PTyr blocks and subsequent deshielding of P(OEGMA-co-SBMA) corona for micelle destruction. Taken together, we developed an efficient approach for the synthesis of enzyme-responsive theranostic zwitterionic conjugated bottlebrush copolymers with a brush-on-brush architecture, and the resulting theranostic micelles with high DLC and tumor microenvironment-specific responsiveness represent a novel nanoplatform for simultaneous cell image and drug delivery.

Photo-switchable supramolecular comb-like polymer brush based on host-guest recognition for use as antimicrobial smart surface

Bacterial infections from biomedical devices pose a great threat to the health of humans and thus place a heavy burden on society. Therefore, developing efficient antibacterial surfaces has attracted much attention. However, it is a challenge to identify or develop a combination that efficiently integrates multiple functions via topological tailoring and on-demand function-switch via non-contact and noninvasive stimuli. To resolve this issue, a highly hydrophilic comb polymer brush was constructed here based on supramolecular host-guest recognition. Azobenzene (azo)-modified antifouling and antibacterial polymers were incorporated into cyclodextrin (CD)-modified antifouling polymer brushes grafted on the surface. The surface thus obtained possessed excellent antifouling performance with a low bacterial density of ∼6.25 × 10⁵ cells per cm² after 48 h and exhibited a high efficiency of ∼88.2% for killing bacteria. Besides, irradiation with UV light resulted in the desorption of the azo-polymers and a release of ∼85.1% attached bacteria. Irradiating visible light led to the re-adsorption of azo-polymers, which regenerated the fresh surface; the process could be repeated for at least three cycles, and the surface still maintained low bacterial attachments with a cell density of ∼7.10 × 10⁵ cells per cm², high sterilization efficiency of ∼93.8%, and a bacteria release rate of ∼83.1% in the 3rd cycle. The photo-switchable antibacterial surface presented in this research will provide new insights into the development of smart biomedical surfaces.

Robust In Situ Fouling Control toward Thin-Film Composite Reverse Osmosis Membrane via One-Step Deposition of a Ternary Homogeneous Metal-Organic Hybrid Layer

Membrane fouling is one of the persistent headaches for water desalination because of the significant detriment to membrane performance and operating cost control. It is a great challenge to overcome such crisis in a facile and robust manner. This work was dedicated to customizing an antifouling thin-film composite (TFC) reverse osmosis (RO) membrane with a polydopamine (PDA)/β-alanine (βAla)/Cu²⁺ ternary homogeneous metal-organic hybrid coating. The metal ions were evenly distributed in a continuous organic network via polydentate coordination. The incorporation of βAla enabled a substantial promotion of the Cu²⁺ loading capacity on the membrane surface. The involved one-step codeposition protocol made the surface engineering practically accessible. The deposition time was optimized to afford an uncompromising permselectivity of the membrane. This novel trinity was a smart blend of anti-adhesive and bactericidal factors, and each component in the all-in-one layer performed its own function. The hydrophilic PDA/βAla phase induced weak deposition propensity of organic foulant and bacteria onto the modified membrane, as elucidated by water flux variation, foulants adhesion profile, and interfacial interaction energy. Meanwhile, the Cu²⁺-loaded surface strongly inactivated the attached bacteria to further alleviate biofouling. Excellent sustainability and stability implied the reliable performance of such trinity-coated membrane in practical service. Given the simplicity and robustness, this work opened a promising avenue for in situ fouling control of TFC RO membranes during water desalination.

Surface characterization of thin-film composite membranes using contact angle technique: Review of quantification strategies and applications

Thin-film composite (TFC) membranes are the most widely used membranes for low-cost and energy-efficient water desalination processes. Proper control over the three influential surface parameters, namely wettability, roughness, and surface charge, is vital in optimizing the TFC membrane surface and permeation properties. More specifically, the surface properties of TFC membranes are often tailored by incorporating novel special wettability materials to increase hydrophilicity and tune surface physicochemical heterogeneity. These essential parameters affect the membrane permeability and antifouling properties. The membrane surface characterization protocols employed to date are rather controversial, and there is no general agreement about the metrics used to evaluate the surface hydrophilicity and physicochemical heterogeneity. In this review, we surveyed and critically evaluated the process that emerged for understanding the membrane surface properties using the simple and economical contact angle analysis technique. Contact angle analysis allows the estimation of surface wettability, surface free energy, surface charge, oleophobicity, contact angle hysteresis, and free energy of interaction; all coordinatively influence the membrane permeation and fouling properties. This review will provide insights into simplifying the evaluation of membrane properties by contact angle analysis that will ultimately expedite the membrane development process by reducing the time and expenses required for the characterization to confirm the success and the impact of any modification.

Surface Design of Liquid Separation Membrane through Graft Polymerization: A State of the Art Review

Surface modification of membranes is an effective approach for imparting unique characteristics and additional functionalities to the membranes. Chemical grafting is a commonly used membrane modification technique due to its versatility in tailoring and optimizing the membrane surface with desired functionalities. Various types of polymers can be precisely grafted onto the membrane surface and the operating conditions of grafting can be tailored to further fine-tune the membrane surface properties. This review focuses on the recent strategies in improving the surface design of liquid separation membranes through grafting-from technique, also known as graft polymerization, to improve membrane performance in wastewater treatment and desalination applications. An overview on membrane technology processes such as pressure-driven and osmotically driven membrane processes are first briefly presented. Grafting-from surface chemical modification approaches including chemical initiated, plasma initiated and UV initiated approaches are discussed in terms of their features, advantages and limitations. The innovations in membrane surface modification techniques based on grafting-from techniques are comprehensively reviewed followed by some highlights on the current challenges in this field. It is concluded that grafting-from is a versatile and effective technique to introduce various functional groups to enhance the surface properties and separation performances of liquid separation membranes.