Biomimetic asymmetric structural polyamide OSN membranes fabricated via fluorinated polymeric networks regulated interfacial polymerization

Theoretical investigation on the conformation of polymer brushes in mixtures of binary solvents

Polymer brushes are extensively used in various applications, such as antifouling coatings and biomedical sensors. Mixed solvents entail versatile regulations on the conformation of polymer brushes. The understanding of the conformation of polymer brushes in mixtures of two solvents, however, is far from mature. In this work, we develop a self-consistent field (SCF) theory and an Alexander-de Gennes (A-dG) theory to examine the chain conformation of polymer brushes in mixtures of two miscible solvents. We systematically investigate how the Flory-Huggins interaction parameters among the three components, the composition of the mixed solvent, the grafting density, and the chain length, influence the brush height and the density profiles of various species. Our calculations exhibit many non-trivial phenomena, such as the collapse of brushes in mixtures of two good solvents and the worsening of solvent quality when adding a good solvent to a poor solvent. The physical mechanisms of these intriguing phenomena are rationalized via the interplay among the chain conformation entropy, the mixing entropy of the two solvents, and the competition in the interactions among the three species. Quantitative comparison between the SCF and the A-dG theories demonstrates that the latter theory can qualitatively capture the variation trends of the brush height and the average concentrations of different species, while the former theory can provide more detailed descriptions on the density profiles of various species in the brush. Our results here not only exhibit the richness and complexity of polymer brushes in mixed solvents but also provide valuable principles for the rational design of stimuli-responsive brushes.

Fabrication and Functional Regulation of Biomimetic Interfaces and Their Antifouling and Antibacterial Applications: A Review

Biomimetic synthesis provides potential guidance for the synthesis of bio-nanomaterials by mimicking the structure, properties and functions of natural materials. Behavioral studies of biological surfaces with specific micro/nano structures are performed to explore the interactions of various molecules or organisms with biological surfaces. These explorations provide valuable inspiration for the development of biomimetic surfaces with similar effects. This work reviews some conventional preparation methods and functional modulation strategies for biomimetic interfaces. It aims to elucidate the important role of biomimetic interfaces with antifouling and low-pollution properties that can replace non-environmentally friendly coatings. Thus, biomimetic antifouling interfaces can be better applied in the field of marine antifouling and antimicrobial. In this review, the commonly used fabrication methods for biomimetic interfaces as well as some practical strategies for functional modulation is present in detail. These methods and strategies modify the physical structure and chemical properties of the biomimetic interfaces, thus improving the wettability, adsorption, drag reduction, etc. that they exhibit. In addition, practical applications are presented of various biomimetic interfaces for antifouling and look ahead to potential biomedical applications. By continuously discovering functional surfaces with biomimetic properties and studying their microstructure and macroscopic properties, more biomimetic interfaces will be developed.

Whether membranes developed for organic solvent nanofiltration (OSN) tend to be hydrophilic or hydrophobic? ── a review

In the past few decades, organic solvent nanofiltration (OSN) has attracted numerous researchers and broadly applied in various fields. Unlike conventional nanofiltration, OSN always faced a broad spectrum of solvents including polar solvents and non-polar solvents. Among those recently developed OSN membranes in lab-scale or widely used commercial membranes, researchers preferred to explore intrinsic materials or introduce nanomaterials into membranes to fabricate OSN membranes. However, the hydrophilicity of the membrane surface towards filtration performance was often ignored, which was the key factor in conventional aqueous nanofiltration. The influence of surface hydrophilicity on OSN performance was not studied systematically and thoroughly. Generally speaking, the hydrophilic OSN membranes performed well in the polar solvents while the hydrophobic OSN membranes work well in the non-polar solvent. Many review papers reviewed the basics, problems of the membranes, up-to-date studies, and applications at various levels. In this review, we have focused on the relationship between the surface hydrophilicity of OSN membranes and OSN performances. The history, theory, and mechanism of the OSN process were first recapped, followed by summarizing representative OSN research classified by surface hydrophilicity and types of membrane, which recent OSN research with its contact angles and filtration performance were listed. Finally, from the industrialization perspective, the application progress of hydrophilic and hydrophobic OSN membranes was introduced. We started with history and theory, presented many research and application cases of hydrophilic and hydrophobic OSN membranes, and discussed anticipated progress in the OSN field. Also, we pointed out some future research directions on the hydrophilicity of OSN membranes to deeply develop the effect made by membrane hydrophilicity on OSN performance for future considerations and stepping forward of the OSN industry.

Recent Advances in the Support Layer, Interlayer and Active Layer of TFC and TFN Organic Solvent Nanofiltration (OSN) Membranes: A Review

Although separation of solutes from organic solutions is considered a challenging process, it is inevitable in various chemical, petrochemical and pharmaceutical industries. OSN membranes are the heart of OSN technology that are widely utilized to separate various solutes and contaminants from organic solvents, which is now considered an emerging field. Hence, numerous studies have been attracted to this field to manufacture novel membranes with outstanding properties. Thin-film composite (TFC) and nanocomposite (TFN) membranes are two different classes of membranes that have been recently utilized for this purpose. TFC and TFN membranes are made up of similar layers, and the difference is the use of various nanoparticles in TFN membranes, which are classified into two types of porous and nonporous ones, for enhancing the permeate flux. This study aims to review recent advances in TFC and TFN membranes fabricated for organic solvent nanofiltration (OSN) applications. Here, we will first study the materials used to fabricate the support layer, not only the membranes which are not stable in organic solvents and require to be cross-linked, but also those which are inherently stable in harsh media and do not need any cross-linking step, and all of their advantages and disadvantages. Then, we will study the effects of fabricating different interlayers on the performance of the membranes, and the mechanisms of introducing an interlayer in the regulation of the PA structure. At the final step, we will study the type of monomers utilized for the fabrication of the active layer, the effect of surfactants in reducing the tension between the monomers and the membrane surface, and the type of nanoparticles used in the active layer of TFN membranes and their effects in enhancing the membrane separation performance.

Ultrathin Polyamide Nanofilms with Controlled Microporosity for Enhanced Solvent Permeation

Organic solvent nanofiltration (OSN) technology shows reduced energy consumption by almost 90% with great potential in achieving low-carbon separation applications. Polyamide nanofilms with controlled intrinsic and extrinsic structures (e.g., thickness and porosity) are important for achieving such a goal but are technically challenging. Herein, ultrathin polyamide nanofilms with controlled microporosity and morphology were synthesized via a molecular layer deposition method for OSN. The key is that the polyamide synthesis is controlled in a homogenous organic phase, rather than an interface, not only involving no monomer kinetic diffusion but also broadening the applicability of amine monomers. The particular nonplanar and rigid amine monomers were superbly used to increase microporosity and the nanofilm was linearly controlled at the nanometer scale to decrease thickness. The composite membrane with the polyamide nanofilms as separation layers displayed highly superior performance to current counterparts. The ethanol and methanol permeances were up to 5.5 and 14.6 L m^-2 h^-1 bar^-1, respectively, but the molecular weight cutoff was tailored as low as 300 Da. Such separation performance remained almost unchanged during a long-term operation. This work demonstrates a promising alternative that could synergistically control the physicochemical structures of ultrathin selective layers to fabricate high-performance OSN membranes for efficient separations.

Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration

In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries.

Recent developments in polymeric nano-based separation membranes

Polymeric nanomaterials, which have tuneable chemical structures, versatile functionalities, and good compatibility with polymeric matrices, have attracted increasing interest from researchers for the construction of polymeric nano-based separation membranes. With their distinctive nanofeatures, polymeric nano-based membranes show great promise in overcoming bottlenecks in polymer membranes, namely, the trade-off between permeability and selectivity, low stability, and fouling issues. Accordingly, recent studies have focused on tuning the structures and tailoring the surface properties of polymeric nano-based membranes via exploitation of membrane fabrication techniques and surface modification strategies, with the objective of pushing the performance of polymeric nano-based membranes to a new level. In this review, first, the approaches for fabricating polymeric nano-based mixed matrix membranes and homogeneous membranes are summarized, such as surface coating, phase inversion, interfacial polymerization, and self-assembly methods. Next, the manipulation strategies of membrane surface properties, namely, the hydrophilicity/hydrophobicity, charge characteristics, and surface roughness, and interior microstructural properties, namely, the pore size and content, channel construction and regulation, are comprehensively discussed. Subsequently, the separation performances of liquid ions/molecules and gas molecules through polymeric nano-based membranes are systematically reported. Finally, we conclude this review with an overview of various unsolved scientific and technical challenges that are associated with new opportunities in the development of advanced polymeric nano-based membranes.

A bioinspired Janus polyurethane membrane for potential periodontal tissue regeneration

Guided tissue regeneration (GTR) is the main therapeutic method for periodontal tissue regeneration. The key to the GTR strategy is the membrane which can assist the reconstruction of bone tissue in the periodontal defect and prevent the migration of epithelium and fibroblasts to the defect. However, the existing periodontal membrane cannot effectively promote periodontal tissue regeneration due to the limited bioactivity and physicochemical function. Here, we developed a bioinspired degradable polyurethane membrane with Janus surface morphology by integrating bioactive dopamine (DA) and an antibacterial Gemini quaternary ammonium salt (QAS). The Janus surface of the membrane is fabricated through spontaneous microphase separation, resulting from the different migration of functional segments between the air-contact upper surface with enriched antibacterial QAS and the substrate-contact bottom with enriched bioactive DA. The smooth surface of the upper membrane used to face the soft tissues can reduce cell adhesion to suppress the migration of fibroblasts, while the rough surface with a topological micro-pit structure of the bottom side facing the bone has excellent function of autonomic mineralization and cell adhesion to promote bone tissue reconstruction. In addition, the membrane containing the antibacterial QAS shows excellent antibacterial effect on common oral pathogens, such as S. aureus and S. mutans. Moreover, the specific dopamine group also endows the membrane with excellent antioxidant efficiency. In vivo research shows that this Janus polyurethane membrane can effectively promote periodontal tissue regeneration in a rat periodontal defect model. Combined with its excellent mechanical properties and biocompatibility, the polyurethane membrane is a promising material for potential periodontal tissue regeneration.

Nanofiltration Membranes with Octopus Arm-Sucker Surface Morphology: Filtration Performance and Mechanism Investigation

Precisely tailoring the surface morphology characteristics of the active layers based on bionic inspirations can improve the performance of thin-film composite (TFC) membranes. The remarkable water adsorption and capture abilities of octopus tentacles inspired the construction of a novel TFC nanofiltration (NF) membrane with octopus arm-sucker morphology using carbon nanotubes (CNTs) and beta-cyclodextrin (β-CD) during interfacial polymerization (IP). The surface morphology, chemical elements, water contact angle (WCA), interfacial free energy (ΔG), electronegativity, and pore size of the membranes were systematically investigated. The optimal membrane exhibited an enhanced water permeance of 22.6 L·m^-2·h^-1·bar^-1, 180% better than that of the TFC-control membrane. In addition, the optimal membrane showed improved single salt rejections and monovalent/divalent ion selectivity and can break the trade-off effect. The antiscaling performance and stability of the membranes were further explored. The construction mechanism of the octopus arm-sucker structure was excavated, in which CNTs and β-CD acted as arm skeletons and suckers, respectively. Furthermore, the customization of the membrane surface and performance was achieved through tuning the individual effects of the arm skeletons and suckers. This study highlights the noteworthy potential of the design and construction of the surface morphology of high-performance NF membranes for environmental application.