Membrane Structural Properties Research Articles

Effect of coagulation bath and amphiphobic modification on the structure and membrane distillation properties of polyvinylidene fluoride membrane

Effect of coagulation bath and amphiphobic modification on the structure and membrane distillation properties of polyvinylidene fluoride membrane

Dopamine hydrochloride and L-arginine Co-functionalized halloysite nanotubes for modification of polyethersulfone ultrafiltration membrane with improved separation performance

In recent years, a range of high-performance ultrafiltration membranes have been developed, but maintaining high retention without sacrificing high throughput remains a serious challenge. In this paper, functionalized halloysite nanotubes is constructed by copolymerization and by a one-step reaction of L-arginine and dopamine hydrochloride using halloysite nanotubes as carriers. Subsequently, modified polyethersulfone membranes are prepared by blending them as additives through non-solvent-induced phase transition separation. As the synthesized nanofillers is rich in functional groups, negative electronegativity, and unique structures, the study focuses on adding nanofillers’ effect on the membrane structure and physicochemical properties. The addition of appropriate nanofillers enhances the membrane surface wettability and negative electronegativity, and the enlarged internal pores and the dense layer that remains flat and homogeneous effectively promote the flux of small molecules, the retention of large molecules, and the cyclic stability of the membrane. The prepared polyethersulfone membranes demonstrate exceptional cycle stability, high separation efficiency (almost 100 % for Congo red), and significantly improved permeation performance (initial permeate flux up to 316.5 L m-2h−1). The results demonstrate the high potential of the modified prepared polyethersulfone membranes for pertinent environmental separation processes.

Biomimetic interlayer brought unexpected enhancement in permeability and rejection of polyamide nanofiltration membrane

Construction of interlayer between porous substrate and polyamide (PA) layer has been proved to be an effective way in improving membrane separation performance by the regulation of membrane structure and chemical properties. In present study, biomimetic material—1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) lipid bilayer was selected to serve as the interlayer prepared by suction filtration due to its unique advantages such as smooth, continuous, uniform and hydrophilic surface. The results showed that DOPE interlayer effectively lowered the diffusion rate of piperazine (PIP) from membrane surface to organic phase and thus contributing to the thinner and smoother PA layer. The permeability of the interlayer-based PA membrane reached 35.9 L/m2·h·bar, which was 190 % higher than pure PA NF membranes. More important, the interlayer-based PA membrane exhibited excellent Na2SO4 rejection about 99.8 % accompanied by a good separation selectivity between univalent and bivalent ions. Besides, the interlayer-based PA membrane possessed good stability to the changes of operating pressure, concentration and pH of feed solution, and the long-term NF test. Meanwhile, it performed well in removing NTU, TOC, Mg2+ and SO42− in the treatment of surface water and showed its potential in the practical application. In all, the present work brought new interlayer material in fabricating high-performance NF membrane.

Residual Membrane Fluidity in Mycobacterial Cell Envelope Layers under Extreme Conditions Underlines Membrane-Centric Adaptation.

One of the routes for adaptation to extreme environments is via remodeling of cell membrane structure, composition, and biophysical properties rendering a functional membrane. Collective studies suggest some form of membrane feedback in mycobacterial species that harbor complex lipids within the outer and inner cell wall layers. Here, we study the homeostatic membrane landscape of mycobacteria in response to high hydrostatic pressure and temperature triggers using high pressure fluorescence, mass and infrared spectroscopies, NMR, SAXS, and molecular dynamics simulations. Our findings reveal that mycobacterial membrane possesses unique and lipid-specific pressure-induced signatures that attenuate progression to highly ordered phases. Both inner and outer membrane layers exhibit phase coexistence of nearly identical lipid phases keeping residual fluidity over a wide range of temperature and pressure, but with different sensitivities. Lipidomic analysis of bacteria grown under pressure revealed lipidome remodeling in terms of chain length, unsaturation, and specific long-chained characteristic mycobacterial lipids, rendering a fluid bacterial membrane. These findings could help understand how bacteria may adapt to a broad spectrum of harsh environments by modulating their lipidome to select lipids that enable the maintenance of a fluid functional cell envelope.

Forward osmosis membrane process: A review of temperature effects on system performance and membrane parameters from experimental studies

Forward osmosis (FO) offers a promising solution for concentration and material recovery, characterized by its low energy consumption and high separation efficiency. Temperature exerts a significant influence on FO, affecting permeation performance, membrane characteristics, and solution chemistry. The review article shows that increasing temperatures enhance forward permeate flux and solvent recovery by modifying mass transfer coefficients, membrane structure, and solution properties like osmotic pressure, diffusivity, and viscosity. This helps alleviate concentration polarization, a key challenge in FO applications. However, higher temperatures can exacerbate reverse solute flux, diminish solute rejection, and amplify membrane fouling, impacting operational efficiency and effluent quality. Studies involving thermoresponsive compounds or high-solute-content solutions yield conflicting results, further complicated by thermo-osmosis in scenarios with temperature gradients between solutions. In water and wastewater treatment, a huge quantity of solutions is treated, and temperature control is difficult. Managing solution temperatures through the utilization of waste hot streams or available heat sources can offer a viable strategy for enhancing system efficiency and mitigating the detrimental impacts of temperature fluctuations, while the solution volume should be effectively reduced before the treatment. A nuanced comprehension of temperature’s impacts is imperative for refining FO systems and addressing challenges across various industrial and environmental sectors.

Piperidinium-incorporated fabrication of high-performance polyamide nanofiltration membrane with high free volume for magnesium/lithium separation

Efficient magnesium-lithium separation is key to extracting lithium resources from salt lake brines. However, efficient magnesium-lithium separation is constrained by the high magnesium-to-lithium ratios on the nanofiltration separation performance due to the weakened Donnan effect and inherent permeability-selectivity trade-off behaviour. To address this challenge, a dual methylpiperidinium ionic liquid was designed in this work and incorporated into polyamide networks to manipulate the structural properties of polyamide membrane for improved magnesium/lithium separation. We demonstrate that the piperidinium modification of polyamide networks not only modulated and enhanced the morphology, hydrophilicity, free volume and electropositivity, but also synergized the steric hindrance differentiation inside the membrane nanochannels. These structural advantages enabled the modified membrane to achieve high-separation performance with enhanced water permeance of 37.3 L m−2 h−1 bar−1 and Mg2+/Li+ selectivity of 30.6 (for Mg/Li mass ratio of 31.2). Molecular dynamics simulations further confirmed that the fast water transport and the difference in the ion separation behaviour are strongly correlated to the enhanced structural properties of membranes. We expect this work to provide insightful guidance for engineering high-performance membranes and make contributions in the application of nanofiltration in lithium mining from high Mg/Li ratio brines.

Machine Learning for Polymer Design to Enhance Pervaporation-Based Organic Recovery.

Pervaporation (PV) is an effective membrane separation process for organic dehydration, recovery, and upgrading. However, it is crucial to improve membrane materials beyond the current permeability-selectivity trade-off. In this research, we introduce machine learning (ML) models to identify high-potential polymers, greatly improving the efficiency and reducing cost compared to conventional trial-and-error approach. We utilized the largest PV data set to date and incorporated polymer fingerprints and features, including membrane structure, operating conditions, and solute properties. Dimensionality reduction, missing data treatment, seed randomness, and data leakage management were employed to ensure model robustness. The optimized LightGBM models achieved RMSE of 0.447 and 0.360 for separation factor and total flux, respectively (logarithmic scale). Screening approximately 1 million hypothetical polymers with ML models resulted in identifying polymers with a predicted permeation separation index >30 and synthetic accessibility score <3.7 for acetic acid extraction. This study demonstrates the promise of ML to accelerate tailored membrane designs.

Long-Chain Lipids Facilitate Insertion of Large Nanoparticles into Membranes of Small Unilamellar Vesicles.

Insertion of hydrophobic nanoparticles into phospholipid bilayers is limited to small particles that can incorporate into a hydrophobic membrane core between two lipid leaflets. Incorporation of nanoparticles above this size limit requires the development of challenging surface engineering methodologies. In principle, increasing the long-chain lipid component in the lipid mixture should facilitate incorporation of larger nanoparticles. Here, we explore the effect of incorporating very long phospholipids (C24:1) into small unilamellar vesicles on the membrane insertion efficiency of hydrophobic nanoparticles that are 5-11 nm in diameter. To this end, we improve an existing vesicle preparation protocol and utilized cryogenic electron microscopy imaging to examine the mode of interaction and evaluate the insertion efficiency of membrane-inserted nanoparticles. We also perform classical coarse-grained molecular dynamics simulations to identify changes in lipid membrane structural properties that may increase insertion efficiency. Our results indicate that long-chain lipids increase the insertion efficiency by preferentially accumulating near membrane-inserted nanoparticles to reduce the thermodynamically unfavorable disruption of the membrane.

Preparation of N-MG-modified PVDF-CTFE substrate composite nanofiltration membrane and its selective separation of salt and dye.

Poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) is considered an ideal membrane material for the treatment of complex environmental water due to its exceptional thermal stability and chemical resistance. Thus, to expand its application in the field of nanofiltration (NF) membranes, in this study, N-methylglucamine (N-MG) was used to hydrophilically modify PVDF-CTFE, overcoming the inherent hydrophobicity of PVDF-CTFE as a porous substrate membrane, which leads to difficulties in controlling the interfacial polymerization (IP) reaction and instability of the separation layer structure. The -OH present in N-MG could replace the C-Cl bond in the CTFE chain segment, thus enabling the hydrophilic graft modification of PVDF-CTFE. The influence of the addition of N-MG on the surface and pore structure, wettability, permeability, ultrafiltration separation, and mechanical properties of the PVDF-CTFE substrate membrane was studied. According to the comparison of the comprehensive capabilities of the prepared porous membranes, the M4 membrane with the addition of 1.5 wt% N-MG exhibited the best hydrophilicity and permeability, indicating that it is a desirable modified membrane for use as an NF substrate membrane. The experiments showed that the rejection of Na2SO4 by the NF membrane was 96.5% and greater than 94.0% for various dyes. In the test using dye/salt mixed solution, this membrane exhibited a good separation selectivity (CR/NaCl = 177.8) and long-term operational stability.

Phospholipid Membranes as Chemically and Functionally Tunable Materials.

The sheet-like lipid bilayer is the fundamental structural component of all cell membranes. Its building blocks are phospholipids and cholesterol. Their amphiphilic structure spontaneously leads to the formation of a bilayer in aqueous environment. Lipids are not just structural elements. Individual lipid species, the lipid membrane structure, and lipid dynamics influence and regulate membrane protein function. An exciting field is emerging where the membrane-associated material properties of different bilayer systems are used in designing innovative solutions for widespread applications across various fields, such as the food industry, cosmetics, nano- and biomedicine, drug storage and delivery, biotechnology, nano- and biosensors, and computing. Here, the authors summarize what is known about how lipids determine the properties and functions of biological membranes and how this has been or can be translated into innovative applications. Based on recent progress in the understanding of membrane structure, dynamics, and physical properties, a perspective is provided on how membrane-controlled regulation of protein functions can extend current applications and even offer new applications.

The intricate link between membrane lipid structure and composition and membrane structural properties in bacterial membranes.

It is now evident that the cell manipulates lipid composition to regulate different processes such as membrane protein insertion, assembly and function. Moreover, changes in membrane structure and properties, lipid homeostasis during growth and differentiation with associated changes in cell size and shape, and responses to external stress have been related to drug resistance across mammalian species and a range of microorganisms. While it is well known that the biomembrane is a fluid self-assembled nanostructure, the link between the lipid components and the structural properties of the lipid bilayer are not well understood. This perspective aims to address this topic with a view to a more detailed understanding of the factors that regulate bilayer structure and flexibility. We describe a selection of recent studies that address the dynamic nature of bacterial lipid diversity and membrane properties in response to stress conditions. This emerging area has important implications for a broad range of cellular processes and may open new avenues of drug design for selective cell targeting.

Impact of SiO2 doping on the structure and oil-water separation properties of a PVDF membrane: insights from molecular dynamics simulation.

Hybrid inorganic particles combined with polymers are widely used to modify the properties of polymer membranes. However, the mechanism by which particles affect membranes remains unclear. This study investigates SiO2-hybridized PVDF membranes through molecular dynamic simulation, focusing on the interaction between SiO2 clusters and PVDF chains. It examines the impact of varying SiO2 concentrations (3.5 wt%, 6.8 wt%, 9.9 wt%, 12.8 wt%, and 15.5 wt%) on membrane stability and structure. The results indicate that adding SiO2 can inhibit PVDF chain mobility in the membrane with minimal effect on fractional free volume (FFV), except for altering interactions between PVDF-PVDF, PVDF-SiO2, and SiO2-SiO2, thereby affecting the structure of hybrid membranes. The adsorption and diffusion behavior of water and oil molecules on these membranes were also studied. It was observed that the adsorption energy and diffusion coefficient initially increase and then decrease with increasing SiO2 concentration, reaching an optimum between 6.8 wt% and 12.8 wt%. This phenomenon is attributed to the ability of optimal SiO2 concentrations to create hydrophilic channels in PVDF membranes, enhancing water affinity and reducing oil affinity. Consequently, water permeation through the hybrid membrane is promoted, improving the efficiency of oil/water separation compared to pure PVDF membranes. This research contributes to understanding the function of adding inorganic particles to polymer membranes and provides insights for designing advanced functional hybrid membranes.

Facile Preparation of PVDF/CoFe2O4-ZnO Hybrid Membranes for Water Depollution.

In this investigation, CoFe2O4-PVDF and CoFe2O4-ZnO-PVDF hybrid membranes were prepared using a modified phase inversion method in which a magnetic field was applied during the casting process to ensure a uniform distribution of nanomaterials on the membrane surface. Thus, better absorption of light and increased participation of nanoparticles in the photodegradation process is ensured. The influence of nanomaterials on the crystalline structure, surface morphology, and hydrophilicity properties of the PVDF membrane was investigated. The obtained results indicated that the hybrid membrane exhibited significant differences in its intrinsic properties due to the nanomaterials addition. The hydrophilicity properties of the PVDF membrane were improved by the presence of nanoparticles. The photocatalytic decomposition of aqueous Rhodamine B solution in the presence of the prepared membrane and under visible light irradiation was tested. The hybrid membrane containing CoFe2O4-ZnO on its surface exhibited a high removal rate.

Fast and sensitive detection of highly toxic thiophenol using β-CD modified nanofibers membrane with promoted fluorescence response

Thiophenols are widely used in chemical and pharmaceutical industries, but the acute toxicity and irritating effects of these chemicals pose a threat to public health. A nanofibrous membrane-based fluorescent and colorimetric sensor was synthesized for the convenient and portable detection of thiophenols relying on the nucleophilic substitution reaction of chlorinated dipyrrole fluoride (BODIPY). To improve the sensing efficiency, β-CD was introduced as an addictive to regulate the molecular structure and physicochemical properties of the substrate membrane. The result showed that β-CD with appropriate cavity had good capability for complexing with the probe BODIPY, which successfully reduced the leakage of BODIPY during used. Also, thiophenol could be enriched by β-CD, and enhanced ratiometric fluorescence responses were achieved. The improved hydrophilicity facilitated the full contact of the NFM with thiophenol, contributing to a fast and efficient sensing process.The sensor system achieves a much shorter response time (180 s) and an extremely lower detection limit (0.11 nM). Furthermore, the sensor's fluorescent color changes can be identified by naked eye, showing great promise for the real-time on-site monitoring of thiophenols in both water and gas phases. Possible sensing mechanisms were investigated through theoretical calculation. Practical feasibility was validated through the actual sample analysis.

Viscosity-Sensitive Membrane Dyes as Tools To Estimate the Crystalline Structure of Lipid Bilayers.

Lipid membranes are crucial for cellular integrity and regulation, and tight control of their structural and mechanical properties is vital to ensure that they function properly. Fluorescent probes sensitive to the membrane's microenvironment are useful for investigating lipid membrane properties; however, there is currently a lack of quantitative correlation between the exact parameters of lipid organization and a readout from these dyes. Here, we investigate this relationship for "molecular rotors", or microviscosity sensors, by simultaneously measuring their fluorescence lifetime to determine the membrane viscosity, while using X-ray diffraction to determine the membrane's structural properties. Our results reveal a phase-dependent correlation between the membrane's structural parameters and mechanical properties measured by a BODIPY-based molecular rotor, giving excellent predictive power for the structural descriptors of the lipid bilayer. We also demonstrate that differences in membrane thickness between different lipid phases are not a prerequisite for the formation of lipid microdomains and that this requirement can be disrupted by the presence of line-active molecules. Our results underpin the use of membrane-sensitive dyes as reporters of the structure of lipid membranes.

Successful preparation of polyaniline‐modified polystyrene novel composite membrane

AbstractThis work describes the polyaniline (PANI) nanoparticles' impregnation into the polystyrene (PS) membrane and its impact on the different membrane properties for the first time. PANI nanoparticles were synthesized separately using the oxidative polymerization technique and then impregnated into the polystyrene‐DMF matrix solution. Membranes were cast via the Non‐Solvent Induced Phase Separation (NIPS) process. The surface and structural properties of the fabricated membranes were thoroughly characterized using contact angle measurement (CA), x‐ray diffraction (XRD), Fourier‐transform infrared spectrometer (FTIR), and scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) and the mechanical characteristics of the membrane were also investigated. According to the CA results, the addition of PANI in the matrix improved the polystyrene membrane's hydrophilicity from 65° to 54.5°. The FTIR spectra revealed that the PANI nanoparticles were successfully impregnated into the PS matrix. SEM images illustrated that the porosity of the PANI‐modified membrane was enhanced by 50% compared to the pristine PS membrane. Furthermore, adding PANI to the PS membrane significantly reduced the average pore size. The filtration experiment showed that PANI modified membrane had 81% rejection of MO dye as compared to the pristine PS membrane which had 60%. Therefore, The PANI added to the PS membrane greatly enhanced the PS membrane's structural properties.

In-situ rapid construction of aliphatic amine combined polyamide seawater reverse osmosis membrane for efficient boron removal

Polyamide (PA) reverse osmosis membranes are commonly employed in seawater desalination owing to their effective salt rejection and water permeability; however, the elimination of small and neutral boron molecules from seawater remains a significant hurdle in energy-efficient and cost-effective desalination processes. In this work, a seawater reverse osmosis (SWRO) membrane with powerful boron removal competence was designed by adopting an in-situ rapid integration protocol, which utilized aliphatic amines as hydrophobic barriers by bonding the residual chloride groups upon the membrane surface and as molecular plugs by embedding in the PA networks. Consequently, it resulted in a notable improvement in the rejection of neutral boron molecules due to enhanced steric hindrance caused by immobilized amine plugs and synergistically tunned hydrophobic interactions. The permeability coefficient of boron decreased from 4.8 to 0.9 L m−2 h−1, and the boron rejection increased from 80.7 to 90.5% under the modification conditions with the optimal type and concentration of amines, while displaying a NaCl rejection of 99.8% and an acceptable water permeability of 0.55 L m−2 h−1 bar−1. Meanwhile, the alteration of membrane chemical compositions and structure properties was kept to a minimum. This study offers intuitive insights into the critical roles played by the aliphatic amines in the selective layer of the membrane for the removal of neutral boron molecules and salts, thereby enabling the fabrication of highly selective SWRO membranes, which may have significant implications for more efficient membrane-based seawater desalination and boron removal.

Effects of pulse repetition rate in static electrochemotherapy models

Electroporation alters cell membrane structure and tissue electrical properties by short and intense pulsed electric fields (PEF). Static mathematical models are often used to explain the change in electrical properties of tissues caused by electroporation. Electric pulse repetition rate may play an important role, as tissue dielectric dispersion, electroporation dynamics, and Joule heating may affect the electrical properties. In this work, we investigate the effects on the magnitude of the electric current when the repetition rate of the standard electrochemotherapy protocol is increased. Liver, oral mucosa, and muscle tissues were studied. Ex vivo animal experiments show that the magnitude of the electric current increases when the repetition rate is changed from 1 Hz to 5 kHz (10.8% for liver, 5.8% for oral mucosa, and 4.7% for muscle). Although a correction factor could reduce the error to less than 1%, dynamic models seem to be necessary to analyze different protocol signatures. Authors should be aware that static models and experimental results can only be compared if they use exactly the same PEF signature. The repetition rate is a key information to consider in the pretreatment computer study because the current at 1 Hz PEF differs from a 5 kHz PEF.

A serendipity of nanofiltration membrane modification using a simple approach: Limited sulfonamidation, remarkable improvements

Surface modification via secondary interfacial polymerization (IP) is a promising technology for the enhancement of nanofiltration (NF) membrane performance such as rejection selectivity. In this study, sulfuryl chloride (SC), containing sulfur element, was employed to introduce sulfonic groups into the active layer of membranes, with a main purpose of investigating the secondary IP mechanisms as well as the variation of membrane structural and physicochemical properties. Moreover, the SC-modified membranes would be endowed with favorable performance. Results showed that SC in a hexane environment behaved similarly with small and reactive diacyl dichloride in enhancing membrane surface negative charge density and contracting membrane pores. Membrane surface characterization showed that the sulfur element had a low concentration with an S/N ratio less than 0.04. This indicated that, on the one hand, the residual amine groups in the nascent active layer for secondary IP were quite limited, and on the other hand, the improvement of membrane performance was remarkably affected by the introduced sulfonyl groups. Consequently, SC in the hexane environment could further enhance the crosslinking degree of the active layer. In addition, SC modification could increase the membrane surface hydrophilicity and narrow the pore size distribution. The SC-modified membranes would be suitable for advanced treatment of drinking water. An optimized membrane with SC modification had a molecular weight cutoff of ∼350 Da and a surface zeta potential of ∼−55.8 mV, and could effectively reject five negatively charged per- and polyfluoroalkyl substances (with molecular weight ranging from 214 to 414 Da) by over 80% while with a low rejection of MgCl2 below 30%..

Preparation and properties of PVA nanofibers with spiral ordered internal structure

The spinning solution of PVA(polyvinyl alcohol) was chosen as the spiral spinning research object. With enough needle length, the macromolecules were straightened and aligned under laminar flow theory. The spiral spinning needle controlled the spiral twisting of the straightened macromolecules. The motion trajectory of titanium dioxide(nanoparticles) in nanofibers was photographed by TEM(transmission electron microscope) under the action of spiral centripetal force, which directly verified the feasibility of the spiral spinning principle. The greater the number of spiral spinning needles, the tighter the spiral arrangement inside the nanofibers and the greater the crystallinity of the nanofibers. The SEM(scanning electron microscope) observation revealed that the diameter of nanofibers had a relationship with the number of spiral spinning needles. When the spiral number of spinning needle was 13, the tensile and bursting properties of the nanofiber membrane were optimal, but when the spiral number of spinning needle was 19, the pore structure, electrical resistance, and antibacterial properties of the nanofiber membrane were optimal.