Polymer Membrane Surface Research Articles

Influences of marine biofouling on the potential responses of polymeric membrane ion-selective electrodes

Using polymeric membrane ion-selective electrodes (ISEs) for reliable long-term marine environmental observations is still a challenge due to the formation of biofilms on electrode surfaces. Unfortunately, the contributions of the specific biofilm components to sensor failure have not been studied. Herein, the influences of the specific biofilm components on the performance of the neutral carrier-based polymeric membrane ISEs are systematically investigated in terms of sensitivity, selectivity, and stability. More importantly, the spatial distributions of these foulants in the fouled sensing membrane phase are studied by confocal laser scanning microscopy for the first time to give insight into the fouling mechanisms. Three typical biochemicals (i.e., proteins, polysaccharides, microbial lipids) in biofilms are selected as the representative foulants. The poly (vinyl chloride)-based CO32--ISEs and K+-ISEs/Ca2+-ISEs have been selected as the model sensors for detection of anions and cations, respectively. Experiments show that depending on the type of the biofoulants, the adsorption of the foulants on the polymeric membrane surface and/or their extraction into the organic membrane phase could occur and induce a change in the potential responses. This study provides a deep insight into the influences of the specific biofilm components on the polymeric membrane ISEs, which is of importance for development of the polymeric membrane marine sensors with high antifouling capabilities for long-term marine monitoring.

High-throughput BCRP inhibitors screening system based on styrene maleic acid polymer membrane protein stabilization strategy and surface plasmon resonance biosensor

Multidrug resistance (MDR) is a dominant challenge in cancer chemotherapy failure. The over-expression of breast cancer resistance protein (BCRP) in tumorous cells, along with its extensive substrate profile, is a leading cause of tumor MDR. Herein, on the basis of styrene maleic acid (SMA) polymer membrane protein stabilization strategy and surface plasmon resonance (SPR) biosensor, a novel high-throughput screening (HTS) system for BCRP inhibitors has been established. Firstly, LLC-PK1 and LLC-PK1/BCRP cell membranes were co-incubated with SMA polymers to construct SMA lipid particles (SMALPs). PK1-SMALPs were thus immobilized in channel 1 of the L1 chip as the reference channel, and BCRP-SMALPs were immobilized in channel 2 as the detection channel to establish the BCRP-SMALPs-SPR screening system. The methodological investigation demonstrated that the screening system was highly specific and stable. Three active compounds were screened out from 26 natural products and their affinity constants with BCRP were determined. The KD of xanthotoxin, bergapten, and naringenin were 5.14 μM, 4.57 μM, and 3.72 μM, respectively. The in vitro cell verification experiments demonstrated that xanthotoxin, bergapten, and naringenin all significantly increased the sensitivity of LLC-PK1/BCRP cells to mitoxantrone with possessing reversal BCRP-mediated MDR activity. Collectively, the developed BCRP-SMALPs-SPR screening system in this study has the advantages of rapidity, efficiency, and specificity, providing a novel strategy for the in-depth screening of BCRP inhibitors with less side effects and higher efficacy.

Bi2WO6 nanoparticles anchored on membrane by grafting via in-situ polymerization for the treatment of antibiotic and pesticides wastewater

Antibiotics, natural organic matter, and pesticides are detected in the ecosystem's domestic water, surface water, and groundwater and are largely applied in pharmaceuticals and agriculture. Polymeric membranes are effectively remove the various pollutants in the water bodies, but fouling is one of the major limitations of commercial membranes. Herein, we modified the polymeric membrane surface with inorganic photocatalytic nanoparticles. In this work, the hydrothermal method is used for the synthesis of Bi2WO6 nanoparticles and as-synthesized nanoparticles grafted onto the various polymeric membranes, including polyetherimide (PEI), cellulose acetate (CA), polyvinylidene fluoride (PVDF), and polysulfone (PSF). The functional group studies confirmed the existence of nanoparticles and hydroxyl groups on the hybrid membrane. Further, finger-like voids, top-surface morphology, and roughness on the membrane surface were validated via Field Emission Scanning Electron Microscopy (FESEM) and Atomic force microscopy (AFM), respectively. The significant rejection of tetracycline, humic acid, and fulvic acid + atrazine was noted with the synthesized membranes in the following order: PVDF (81.1%, 78.8%, 80.6%) > CA (70.1%, 69.3%, 71.7%) > PSF (72.5%, 73.6%, 67.1%) > PEI (75.9%, 65.5%, 63.7%). The photodegradation efficiency of hybrid membranes against tetracycline, humic acid, and fulvic acid + atrazine was observed in the order: PEI (28.5%, 25.8%, 30.2%) < CA (46.5%, 42.4%, 40.5%) < PSF (46.9%, 37.7%, 44.7%) < PVDF (67.7%, 62.1%, 64.3%). These membranes exhibit an outstanding permeate flux recovery ratio to the neat membrane. Therefore, the grafting of Bi2WO6 nanoparticles creates a potential bonding with PVDF membranes than other polymeric membranes, thus exhibiting an outstanding rejection than hybrid and neat membranes.

Protein-activated atomic layer deposition for robust crude-oil-repellent hierarchical nano-armored membranes

Atomic layer deposition (ALD) offers unique capabilities to fabricate atomically engineered porous materials with precise pore tuning and multi-functionalization for diverse applications like advanced membrane separations towards sustainable energy-water systems. However, current ALD technique is inhibited on most non-polar polymeric membranes due to lack of accessible nucleation sites. Here, we report a facile method to efficiently promote ALD coating on hydrophobic surface of polymeric membranes via novel protein activation/sensitization. As a proof of concept, TiO2 ALD-coated membranes activated by bovine serum albumin exhibit remarkable superhydrophilicity, ultralow underwater crude oil adhesion, and robust tolerance to rigorous environments including acid, alkali, saline, and ethanol. Most importantly, excellent cyclable crude oil-in-water emulsion separation performance can be achieved. The mechanism for activation/sensitization is rooted in reactivity for a particular set of amino acids. Furthermore, the universality of protein-sensitized ALD is demonstrated using common egg white, promising numerous potential usages in biomedical engineering, environmental remediation, low-carbon manufacturing, catalysis, and beyond.

Effect of Radio Frequency Irradiation on Dynamics of Luminescence from Surface of Polymer Membrane under UV Excitation in Aqueous Suspensions of Metal Submicron Particles

Effect of Radio Frequency Irradiation on Dynamics of Luminescence from Surface of Polymer Membrane under UV Excitation in Aqueous Suspensions of Metal Submicron Particles

Flexible metal membrane integrated electrified and catalytic attributes for multifunctional water purification with enhanced scaling resistance

Electrified and ceramic membranes assembled with rigid materials have been greatly appreciated for unique electrical responsiveness and catalytic properties for efficient water purification. However, the intensive van der Waals forces of traditional rigid materials have historically resulted in poor rejection, scaling resistance and mechanical properties to those of standard filters. In response, an innovative fabrication approach has been formulated, entailing induced fit theory inspired activation of inert polyamide (PA) substrates, concomitantly coupled with the in-situ growth of CoOx nanoflowers on the polymer membrane surfaces. This method yielded activated terminal amide groups that enable specific coordination in a manner akin to that of a zymogen activation. The ensuing development of CoOx nanoflowers engendered a notably rugged interface, prompting the emergence of grass-like membrane structures reminiscent of the lotus effect. The integration of CoOx nanoflowers endowed the resultant membrane augmented surface hydrophilicity, elevated rejection efficiency, exceptional conductivity, and degradation potential. These effects synergistically yielded an exceptional water permeability for the fabricated membrane (1.90×103 L·m−2·h−1), surpassing that of the CoOx-free control membrane by over twofold, coupled with a separation rate exceeding 99.8 %. Furthermore, interface engineering contributed to an exceptionally high reaction rate constant of the resultant membrane (2.93), surpassing that of the inherent membrane by over 167-fold. Importantly, the self-cleaning prowess, facilitated by CoOx, was evidenced by the recoverability of severely fouled membranes through PMS rinsing and electrical interaction. The mechanisms underlying the membrane's multifaceted antifouling performance were systematically unveiled through the extended Derjaguin-Landau-Verwey-Overbeek theory. By employing the facile and ingenious induced fit theory, this approach ushers forth an extraordinary avenue for water purification and scaling resistance applications, distinctly accentuating the innovative essence of this study.

Surface Treatment of Polymer Membranes for Effective Biofouling Control.

Membrane biofouling is the consequence of the deposition of microorganisms on polymer membrane surfaces. Polymeric membranes have garnered more attention for filtering and purifying water because of their ease of handling, low cost, effortless surface modification, and mechanical, chemical, and thermal properties. The sizes of the pores in the membranes enable micro- and nanofiltration, ultrafiltration, and reverse osmosis. Commonly used polymers for water filter membranes are polyvinyl chloride (PVA), polyvinylidene fluoride (PVDF), polyamide (PA), polyethylene glycol (PEG), polyethersulfone (PES), polyimide (PI), polyacrylonitrile (PAN), polyvinyl alcohol (PA), poly (methacrylic acid) (PMAA), polyaniline nanoparticles (PANI), poly (arylene ether ketone) (PAEK), polyvinylidene fluoride polysulfone (PSF), poly (ether imide) (PEI), etc. However, these polymer membranes are often susceptible to biofouling because of inorganic, organic, and microbial fouling, which deteriorates the membranes and minimizes their lives, and increases operating costs. Biofouling infection on polymer membranes is responsible for many chronic diseases in humans. This contamination cannot be eliminated by periodic pre- or post-treatment processes using biocides and other chemicals. For this reason, it is imperative to modify polymer membranes by surface treatments to enhance their efficiency and longevity. The main objective of this manuscript is to discuss application-oriented approaches to control biofouling on polymer membranes using various surface treatment methods, including nanomaterials and fouling characterizations utilizing advanced microscopy and spectroscopy techniques.

Effects of Low-Frequency Randomly Polarized Electromagnetic Radiation, as Revealed upon Swelling of Polymer Membrane in Water with Different Isotopic Compositions.

Photoluminescence from the surface of Nafion polymer membrane upon swelling in water under irradiation by electromagnetic waves at a frequency of 100 MHz was studied. In these experiments, natural deionized (DI) water with a deuterium content of 157 ppm and deuterium-depleted water (DDW, deuterium content is 1 ppm) were explored. We have studied for the first time the effect of linearly and randomly polarized low-frequency electromagnetic radiation on the luminescence excitation. To obtain low-frequency electromagnetic radiation with random polarizations, anisotropic solid submicron-sized particles, which result in depolarization effects upon scattering of the initially linearly polarized radiation, were used. We compared two types of colloidal particles: spherically symmetric (isotropic) and elongated (anisotropic). If the radiation is linearly polarized, the intensity of luminescence from the Nafion surface decreases exponentially as the polymer is soaked, and such a behavior is observed both in natural DI water and DDW. When spherically symmetric submicron-sized particles are added to a liquid sample, the luminescence intensity also decreases exponentially upon swelling in both natural DI water and DDW. At the same time, when anisotropic submicron-sized particles are added to DI water, random jumps in the luminescence intensity appear during swelling. At the same time, the exponential decrease in the luminescence intensity is retained upon swelling in DDW. A qualitative theoretical model for the occurrence of random jumps in the luminescence intensity is presented.

Ультранизкочастотные осцилляции интенсивности люминесценции полимерной мембраны в водных растворах солей

The paper studies luminescence from the Nafion polymer membrane surface at its swelling in the isotonic aqueous solutions and bi-distilled water using the experimental photo luminescent spectroscopy. Liquid samples were preliminarily treated with the electric pulses with duration of 1 µs and amplitude of 0.1 V using antenna in the form of a flat capacitor. Experiments in photo luminescent spectroscopy were carried out 20 min after the electric pulse treatment. Typical luminescence intensity dependence on the membrane swelling time could be represented as the exponentially decreasing function. Characteristic decay time of the corresponding functions and stationary level of the membrane luminescence intensity depend on the electrical pulses repetition rate. The obtained dependencies could well be reproduced. However, dependence of the luminescence intensity at certain pulse repetition rates appears to be a random function, and the reproducibility is missing. It could be assumed that these stochastic effects are associated with exposure to random external force of the electromagnetic nature acting on the polymer membrane during swelling. Low-frequency pulsations of neutron stars or white dwarfs are the source of this random force according to the authors of the work. This effect is associated with depolarization during the low-frequency electromagnetic field scattering caused by the neutron stars pulsation. Depolarization effect arises due to scattering on long-living anisotropic clusters of nano-bubbles, which, in turn, are becoming anisotropic in the external field of a flat capacitor. Depolarized scattered radiation causes stochastic oscillations of the polymer fibers unwound into the bulk liquid. In this case, luminescence should also acquire the stochastic character taking into account the effect of resonant luminescence energy transfer from a donor to the luminescence acceptor

Self-healing Fuel Cells by Biological Actuators

A completely novel approach aims to extend the lifetime of polymer electrolyte membrane fuel cells (PEM-FCs) many times over through a self-healing mechanism, thus contributing to the transition to a sustainable economy and mobility. Many start-up cycles in truck or car applications lead to pinholes in the proton-conducting polymer membranes (Nafion™). Since there is no way to repair this type of defect when the fuel cell is already assembled, the performance of the fuel cell stack is continuously reduced towards the end of its lifetime. The BioHealing project, an interdisciplinary consortium at the Karlsruhe Institute of Technology, investigates an innovative biohybrid technology that can repair occurring pinholes selectively in fuel cell membranes by a self-healing mechanism without disassembling the fuel cell stack. This is enabled by a biohybrid system, i.e., integrating biological and technical components. The filler-forming enzymes are functionally immobilised on the polymer membrane surface via a special peptide linker to enable site-directed filler production during membrane electrode assembly. For self-healing, a substrate is injected into the gas inlet of the fuel cell stack, the enzymatic reaction is catalysed, and the substrate is converted into the filler, a biological polymerised product that seals the existing pinholes. In this publication, the concept is presented with initial research results. The concept includes characterisation of surface properties and functional groups of the Nafion™ membrane, immobilisation of the specially designed fluorophilic peptide linker, selection of suitable enzymes to be screened for activity and stability, and investigation of the filler to be successfully esterified with the membrane.

Facile self-assembly-based fabrication of a polyvinylidene fluoride nanofiber membrane with immobilized titanium dioxide nanoparticles for dye wastewater treatment

Photocatalytic membrane technology has received significant research attention because this system can continuously and safely purify wastewater without the post-process of separating and recovering the nanoscale photocatalysts. However, conventional membrane technology cannot wholly derive the photocatalytic performance due to the limitation in the loading contents of nanoscale photocatalyst and the reduced reactive sites. In this study, in order to overcome these issues and the limitations of current fabrication methods for photocatalytic membranes, a versatile and facile self-assembly approach for a polyvinylidene fluoride (PVDF) fiber-based reusable photocatalytic membrane with immobilized titanium dioxide (TiO2) nanoparticles is demonstrated to maximize the loading contents and photocatalytic reaction sites of nanoparticles on the surface of polymeric membrane. The TiO2 nanoparticles were successfully immobilized in high loading content on the surface of electrospun PVDF fibers using a poly(styrene-alt-maleic anhydride) as a self-assembly reaction agent at room temperature. Then, the physicochemical properties of the fabricated photocatalytic membrane and the manufacturing mechanism are systematically characterized. The photocatalytic properties of the membrane according to the loading of immobilized TiO2 nanoparticles are evaluated based on the degradation of various dye solutions under the illumination of a Xenon lamp (incident light intensity = 100 mW/cm2). The photocatalytic performance of the membrane is considerably enhanced when the loading of immobilized TiO2 nanoparticles on the PVDF fibers is higher as a result of a more vigorous self-assembly reaction. Furthermore, the reusability of the membrane is evaluated by repeating the dye removal process via adsorption and light irradiation; after the 20th cycle, it is demonstrated that the dye removal efficiency remains high without any leakage of TiO2 nanoparticles. The proposed facile fabrication method for a photocatalytic membrane with excellent reusability thus offers a new approach for the design of industrially applicable high-efficiency photocatalytic membranes.

Adsorption of Methylene Blue on the Surface of Polymer Membrane; Dependence on the Isotopic Composition of Liquid Matrix.

As was found in our previous works, when Nafion swells in water, polymer fibers unwind into the bulk of the surrounding liquid. This effect is controlled by the content of deuterium in water. Here, we present the results of studying the dynamics of methylene blue (MB) adsorption on the Nafion surface for MB solutions based on natural water (deuterium content is 157 ppm, the unwinding effect occurs) and based on deuterium-depleted water (DDW; deuterium content is 3 ppm, there is no unwinding). In addition, we studied the dynamics of water desorption during drying of the Nafion polymer membrane after soaking in MB solution based on natural water and DDW. It turned out that in the case of natural water, the rate of MB adsorption and water desorption is higher than in the case of DDW. It also turned out that the amount of MB adsorbed on the membrane in the case of natural water is greater than in the case of DDW. Finally, it was found that the desorption of water during drying is accompanied by a rearrangement of the absorption spectrum of Nafion. This rearrangement occurs earlier in the case of DDW. Thus, by infinitesimal changes in the deuterium content (from 3 to 157 ppm) in an aqueous solution, in which a polymer membrane swells, we can control the dynamics of adsorption and desorption processes. A qualitative model, which connects the observed effects with the slowing down of diffusion processes inside the layer of unwound fibers, is proposed.

Fabrication of Polymer Membrane Enzyme Reactors with a Dual-Responsive Feature for Cascade Enzyme Reaction Regulation.

Enzymes are known to drive biological processes efficiently and uniquely. However, the integration of multienzymes and immobilization technology to improve the stability of enzymes and boost the catalytic efficiency in cascade reactions by controlling the biocatalysis process in complex conditions via an external stimulus is still facing a significant challenge. Herein, we demonstrate a concept for cascade enzyme reaction regulation by controlling the catalytic efficiency step by step based on a dual-stimuli-responsive porous polymer membrane enzyme reactor (DPMER). Poly(styrene-maleicanhydride-acrylic acid-4-[(4-methacryloyloxy)phenylazo] benzoic acid) was designed for the fabrication of the DPMER with glutaminase and alanine aminotransferase as the model modified enzymes. Under UV light irradiation and by regulating the solution pH, the cascade enzyme reaction was carried out step by step. The polymer membrane surface demonstrated a configuration change while improving the enzymolysis efficiency of the DPMER. The enzymatic kinetics of the DPMER was investigated by a chiral capillary electrophoresis technique, and the cascade enzyme reaction regulation capability was evaluated. Under pH of 4.9 and 365 nm UV irradiation, the poly(4-[(4-methacryloyloxy)phenylazo] benzoic acid) and poly(acrylic acid) moieties changed from a "stretched state" to a "curled state" to form surface nanopores, which embedded the enzymes into the surface nanopores while causing the spatial confinement effect and enhancing the enzymolysis efficiency of the DPMER by 9.9-fold in comparison with the free enzymes. This concept provided a potential platform for cascade enzyme reaction regulation and highlighted the perspective of stimuli-responsive polymers.

Possibility to Alter Dynamics of Luminescence from Surface of Polymer Membrane with Ultrasonic Waves.

The temporal dynamics of luminescence from the surface of Nafion polymer membranes have been studied. In fact, the polymer membrane was soaked in liquids with different contents of deuterium. The test liquids were ordinary (natural) water (deuterium content equal to 157 ppm) and deuterium-depleted water (deuterium content is equal to 3 ppm). Simultaneously with the excitation of luminescence, the Nafion plate was irradiated with ultrasonic pulses, having a duration of 1 μs. The ultrasonic waves were generated with different repetition rates and amplitudes, and irradiated the surface of Nafion in the geometry of grazing or normal incidence. Luminescence regimes were studied when the membrane was irradiated with one ultrasonic wave (one piezoelectric transducer) or two counter-propagating waves (two piezoelectric transducers). It turned out that ultrasonic waves, which fall normal to the membrane interface, do not affect the dynamics of luminescence. At the same time, in the case of ultrasonic irradiation in the grazing incidence geometry, sharp jumps in the luminescence intensity occur, and the behavior of these jumps substantially depends on the mode of irradiation: one or two piezoelectric transducers. This allows for control of the dynamics of luminescence from the polymer surface. In accordance with this model, the possibility of altering the luminescence dynamics is due to the effect of unwinding the polymer fibers from the surface toward the liquid bulk upon soaking. It is important that such unwinding does not occur in deuterium-depleted water, which was confirmed in a direct experiment with dynamic light scattering from polydisperse aqueous suspensions of Nafion nanometer-sized particles; these suspensions were prepared in ordinary water and deuterium-depleted water. Thus, ultrasonic irradiation affects the dynamics of luminescence only when Nafion is swollen in ordinary water; in the case of deuterium-depleted water this effect is missed.

Ion-exchange membrane impact on preferential water transfer in all-vanadium redox flow battery

Preferential water transfer (PWT) is an important issue in vanadium flow batteries, which affects the cycling time. In this work, we propose a new way to control PWT by membrane modification. To assess PWT quantitatively, we developed an accurate method of water volume determination by optical monitoring of an anolyte. As result, we show that PWT for cation-, anion-exchange, and amphoteric benchmark membranes have opposite directions. Thus, we propose control of PWT by balancing concentrations of cation and anion groups on the polymer membrane surface. We modify Nafion 115 membrane by layer-by-layer modification. We use ATR-FTIR spectroscopy, AFM, and Kelvin probe, to track charged layer formation on the polymer membrane surface. The results of the observation show vanadium permeability drop seven times and proton conductivity decreased to 30 mS cm-1 with three times PWT suppression. We demonstrate a low capacity fade (70% vs 46% after 100 cycles for modified and non-modified membranes), and high energy efficiency (91%) for the two bilayer modified membranes. Thus, surface functionalization of ion-exchange membranes is one of the new ways of PWT control.

Surface and Interface Engineering of Polymer Membranes: Where We Are and Where to Go

Surface and interface engineering provides a powerful tool to tailor the structures and properties of polymer membranes, sharpening their applications in sustainable development. Tremendous progress has been achieved in this field over the past 20 years. In this Perspective, we overview the conventional and emerging strategies for membrane surface engineering and present the current trends in surface and interface engineering for both porous and thin-film composite membranes. For porous membranes, the rise of Janus membranes motivates the evolution from uniform functionalization to asymmetric performance construction. For thin-film composite membranes, the research foci are moving to the surface modification of substrates, the fabrication of nanostructured interlayers, and especially the regulation of interfacial polymerization.

Increasing the efficiency of reduced graphene oxide obtained via high temperature electrospun calcination process for the electrochemical detection of dopamine

• XRD confirms the crystalline nature of reduced graphene oxide by using thermal annealing at 500 °C and 600 °C. • XPS analysis confirmed the successful removal of oxygenated groups from the surface of polymeric membrane at higher temperature. • The removal of excess oxygenated groups such as epoxy, carboxyl and hydroxyl resulted in the improved conduction of graphite structure in rGO. • Application of the developed material for the electrochemical detection of dopamine after modification of screen printed carbon electrode. Reduced graphene oxide (rGO) has attracted significant attention for electrochemical sensing applications. In this work, rGO was obtained by thermal annealing of electrospun polymeric nanofiber membrane at 500 and 600 °C. The XRD patterns reveals the phase and crystalline formation of rGO. The interlayer spacing decreases at higher temperature that indicates the removal of oxygen containing moieties. FTIR spectrum shows the absence of epoxy, carboxyland hydroxylgroups for rGO-600 that resembles the surface feature of rGO. XPS further corroborates the XRD and FTIR results and quantifies the predominant functional groups in rGO-500 and rGO-600 °C. The synthesized materials were applied for the electrochemical sensing of dopamine (DA) by cyclic voltammetry. In the case of rGO-500/SPCE, a linear relationship for the DA concentration wasobserved in the range of 0.5 µM to 20 µM with a detection limit of 1.11 µM. Whereas, rGO-600/SPCEalso gave a linear relationship for the DA concentration in the range of 0.5 µM to 20 µM with 1.23 µM detection limit. These electrodes showed good electrocatalytic activity for the oxidation of DA with a minute variation in their detection limit. Therefore, the annealed material rGO can be efficiently used for the quantitative analysis of dopamine after carefully controlling the surface functional groups.

The Role of Cation Hydrophobicity on Ion Transport Selectivity in Nanopore Membranes

Quaternary ammonium salts (QAS) are cationic surfactants widely used in domestic and industrial products like detergents, disinfectants, personal care products, and more. Due to their substantial use, QAS are accidentally or intentionally released into the environment and have been detected in surface waters, wastewaters, and soil sediments. The concentration of QAS in groundwaters has greatly increased, and this poses serious health threats. Therefore, various methods to purify wastewaters and remove the containment QAS have been proposed. Membrane-based technologies have been used extensively, and wastewater treatment facilities often use polymeric membrane-based systems for purification. Quaternary ammonium salts are known to accumulate on the polymeric membrane surfaces and within the membrane pores. This leads to membrane fouling, which is a major obstacle for efficient operation of these membrane systems. Direct evidence is presented here for the adsorption of aqueous QAS adsorbed on a polycarbonate membrane studied. Potentiometric experiments, in accordance with surface contact angle and infrared spectroscopy measurements, illustrate the extent of adsorption on the membrane surface and within the membrane nanopores. Using a homologous quaternary ammonium series, we focus on how the hydrophobicity of the adsorbing cationic surfactant directly affects membrane separation performance, specifically cation transport and membrane permselectivity. It was found that the strength of the interaction between the QAS and the polycarbonate membrane was directly proportional to QAS hydrophobicity (i.e. carbon number). Excessive adsorption to the membrane surface and pore walls deteriorated membrane separation performance and required extra rinsing using an aqueous KCl solution to remove the QAS foulant.

Dynamics of Polymer Membrane Swelling in Aqueous Suspension of Amino-Acids with Different Isotopic Composition; Photoluminescence Spectroscopy Experiments.

In photoluminescence spectroscopy experiments, the interaction mode of the polymer membrane Nafion with various amino-acids was studied. The experiments were performed with physiological NaCl solutions prepared in an ordinary water (the deuterium content is 157 ± 1 ppm) and also in deuterium-depleted water (the deuterium content is ≤1 ppm). These studies were motivated by the fact that when Nafion swells in ordinary water, the polymer fibers are effectively “unwound” into the liquid bulk, while in the case of deuterium-depleted water, the unwinding effect is missing. In addition, polymer fibers, unwound into the liquid bulk, are similar to the extracellular matrix (glycocalyx) on the cell membrane surface. It is of interest to clarify the role of unwound fibers in the interaction of amino-acids with the polymer membrane surface. It turned out that the interaction of amino-acids with the membrane surface gives rise to the effects of quenching luminescence from the luminescence centers. We first observed various dynamic regimes arising upon swelling the Nafion membrane in amino-acid suspension with various isotopic content, including triggering effects, which is similar to the processes in the logical gates of computers.

Coupled Monte Carlo and Molecular Dynamics Simulations on Interfacial Properties of Antifouling Polymer Membranes.

We use molecular simulation to study the wetting behavior of antifouling polymer-tethered membranes. We obtain the interfacial properties (e.g., contact angle) of water at various temperatures for five polymer membranes, including a base polysulfone (PSF) membrane and four other PSF membranes grafted with antifouling polymers (two poly(ethylene glycol) (PEG) tethers and two zwitterionic tethers). We implement a coupled Monte Carlo (MC)/molecular dynamics (MD) approach to determine the interface potentials of water on the membrane surfaces in an efficient manner. Within this method, short MC and MD simulations are performed in cycles to collect the surface excess free energy of a thin water film on polymer membrane surfaces. Simulation results show that the grafting of zwitterionic tethers provides a more significant enhancement in the hydrophilicity of the PSF membrane than that of the PEG tethers. Water completely wets the surface of zwitterionic polymer membranes.