Membrane Mechanical Stability Research Articles

The underlying mechanical properties of membranes tune their ability to fuse

Membrane fusion is a ubiquitous process associated with a multitude of biological events. Although it has long been appreciated that membrane mechanics plays an important role in membrane fusion, the molecular interplay between mechanics and fusion has remained elusive. For example, although different lipids modulate membrane mechanics differently, depending on their composition, molar ratio, and complex interactions, differing lipid compositions may lead to similar mechanical properties. This raises the question of whether (i) the specific lipid composition or (ii) the average mesoscale mechanics of membranes acts as the determining factor for cellular function. Furthermore, little is known about the potential consequences of fusion on membrane disruption. Here, we use a combination of confocal microscopy, time-resolved imaging, and electroporation to shed light onto the underlying mechanical properties of membranes that regulate membrane fusion. Fusion efficiency follows a nearly universal behavior that depends on membrane fluidity parameters, such as membrane viscosity and bending rigidity, rather than on specific lipid composition. This helps explaining why the charged and fluid membranes of the inner leaflet of the plasma membrane are more fusogenic than their outer counterparts. Importantly, we show that physiological levels of cholesterol, a key component of biological membranes, has a mild effect on fusion but significantly enhances membrane mechanical stability against pore formation, suggesting that its high cellular levels buffer the membrane against disruption. The ability of membranes to efficiently fuse while preserving their integrity may have given evolutionary advantages to cells by enabling their function while preserving membrane stability.

Solution-processable poly(ether-ether-ketone) membranes for organic solvent nanofiltration: from dye separation to pharmaceutical purification

Through polymer engineering, the membrane properties can be considerably changed and its performance can be improved. Organic solvent nanofiltration (OSN) membranes require polymers with good solution processability to facilitate membrane preparation. However, the resultant membranes should have excellent solvent resistance. Poly(ether-ether-ketone) (PEEK) is a potential polymer for OSN applications because of its high thermal stability and excellent solvent resistance. However, commercial PEEK has limited solution processability, and its fabrication requires a harsh acidic environment. Herein, two customized PEEKs were synthesized by incorporating methyl (–CH3) and sulfonyl (SO2) groups into the polymer backbone. The membranes were prepared by phase inversion using N-methyl-2-pyrrolidone (NMP) and TamiSolve as a green alternative. The effects of the polymer structure, green solvent, and crosslinking on the membrane morphology, chemical and mechanical stability, as well as separation performance have been examined. The molecular interaction between organic solvents and PEEKs were investigated through molecular dynamic simulations and density functional theory. The molecular weight cutoff (MWCO) values of the membranes were 540–768 g mol−1, with a high corresponding permeance of 8.2–20 L m−2 h−1 bar−1 in acetone. The long-term stability of membranes was successfully demonstrated over two weeks through a continuous crossflow filtration using acetone under a pressure of 30 bar. The membranes demonstrated excellent active pharmaceutical ingredient purification through the removal a 2-methoxyethoxymethyl chloride (125 g mol−1) carcinogenic impurity from roxithromycin (837 g mol−1).

Performance evaluation of polyethersulfone membranes modified with poly (acrylic acid‐co‐N‐vinyl pyrrolidone) grafted mesoporous carbon nitride for effective removal of cadmium(II) from wastewater

AbstractIndustrial pollutants in water streams, such as heavy metals, are among the most important issues for ecosystem and human health. Membrane filtration is an appealing technique for the removal of these contaminants from wastewater. In this study, composite ultrafiltration polyethersulfone (PES) membranes were fabricated by implementing poly (acrylic acid‐co‐N‐vinyl pyrrolidone) grafted mesoporous carbon nitride (MCN) nanoparticles to improve the performance of membranes. Polymer grafted MCN was synthesized through (3‐methacryloxypropyl)trimethoxysilane and (3‐Aminopropyl)triethoxysilane treatment and subsequent in situ radical polymerization on MCN. Modified membranes exhibited significantly improved hydrophilicity; the contact angle decreased from 66° for the PES membrane to 36° for the modified membranes. In addition, the morphology, surface roughness, thermal stability, and mechanical stability of membranes were studied. The results revealed that the pure water flux of membranes was improved from 82.6 to 329. 8 L/m2 h by increasing the nano‐additive content. Moreover, the membranes showed a maximum rejection of 92.3% for Cd2+ metal ions. Studying the fouling resistance of membranes showed a significant increase in fouling ratio recovery from 42.77% to 87.64%. It was also found that the irreversible fouling values were remarkably reduced because of the higher hydrophilicity of fabricated composite membranes.

A Comparison of Unmodified and Sawdust Derived-Cellulose Nanocrystals (CNC)-Modified Polyamide Membrane Using X-ray Photoelectron Spectroscopy and Zeta Potential Analysis

Cellulose nanocrystals (CNC) obtained from waste sawdust were used to modify the polyamide membrane fabricated by interfacial polymerization of m-phenylene-diamine (MPDA) and trimesoyl chloride (TMC). The efficiency of the modification with sawdust-derived CNC was investigated using zeta potential and X-ray photoelectron spectroscopy (XPS). The effect of the modification on membrane mechanical strength and stability in acidic and alkaline solutions was also investigated. Results revealed that the negative zeta potential decreased at a high pH and the isoelectric point shifted into the acidic range for both modified and unmodified membranes. However, the negative charges obtained on the surface of the modified membrane at a pH lower than 8 were higher than the pristine membrane, which is an indication of the successful membrane modification. The XPS result shows that the degree of crosslinking was lowered due to the presence of CNC. Enhanced stability in solution in all pH ranges and the increase in mechanical strength, as indicated by higher Young's modulus, maximum load, and tensile strength, confirmed the robustness of the modified membrane.

Engineering a superwetting membrane with spider-web structured carboxymethyl cellulose gel layer for efficient oil-water separation based on biomimetic concept

Superhydrophilic and underwater superoleophobic membranes have recently attracted significant interest as materials for effective oil-water emulsion separation.In this work, a superwetting membrane with a spider web structured gel layer was designed for efficient oil-water separation. Biomaterial, carboxymethyl cellulose (CMC), was used as the raw material, a spider web structured gel layer was constructed on the PVDF membrane surface by heat-treatment and chemical cross-linking. The hydrophilic gel layer imparted excellent superhydrophilic and underwater superoleophobic properties to the membrane, while the special spider web structure improved the membrane mechanical stability. The fabricated membrane exhibited superhydrophilicity and underwater superoleophobicity. Among different CMC concentration-modified membranes, the M-0.5 membrane containing 0.5 wt% CMC exhibited a flux of 612 L·m−2 h−1 during dichloromethane oil-water emulsion separation, which was 4.2-fold higher than that of the pristine PVDF membrane, while the membrane showed efficient oil-water separation capacity. Additionally, the water flux recovery reached as high as 93.3 %, and oil rejection attained 99.1 %. Meanwhile, the spiderweb-structured gel layer on the membrane surface displayed good mechanical stability. In summary, this novel membrane-modification method, inspired by the spider web structure, was simple, cost effective and environmentally friendly, thereby making it promising for future preparation of highly efficient oil-water emulsion separation membranes.

Beaded electrospun polyvinylidene fluoride (PVDF) membranes for membrane distillation (MD)

A new class of PVDF-based membranes suitable for membrane distillation were prepared via electrospinning. The classical fiber morphology of PVDF electrospun membranes was changed to generate a beaded structure by tuning the solvent ratio and operating parameters during membrane fabrication. Results showed that by increasing the N, N-Dimethylacetamide (DMAC) to acetone ratio used to prepare the PVDF solution, PVDF micron-sized beads can be created within the fiber structure of the electrospun membrane. This is mainly ascribed to the lower saturated vapor pressure of the DMAC, which is slowing the polymer solidification rate, resulting in a fiber-to-bead morphology. An increase in the bead density induces an increase of the WCA of the resulting membrane (from 134° to 148°), with a concomitant reduction of the membrane thickness. Large bead-to-fiber ratios may be obtained by working with low PVDF concentration (17 wt%) but at the expense of membrane mechanical stability. The latter can be enhanced by increasing the PVDF solution concentration. The results show that simultaneous deployment of 17 and 25 wt% of PVDF solutions in a double-needle electrospinning device enables the fabrication of electrospun PVDF-beaded membranes with high hydrophobicity, low thickness and good mechanical stability for membrane distillation. The best membrane showed a 34% increase in membrane permeability and maintained a more stable water flux compared to a commercial PVDF membrane when filtering hypersaline solution in high-recovery direct contact membrane distillation. Thus beaded PVDF structured electrospun structures may represent a facile method to improve PVDF membrane performance in MD applications.

3D-printed bi-layered polymer/hydrogel construct for interfacial tissue regeneration in a canine model

ObjectivesThere are complications in applying regenerative strategies at the interface of hard and soft tissues due to the limited designs of constructs that can accommodate different cell types in different sites. The problem originates from the challenges in the adhesion of dissimilar materials, such as polymers and hydrogels, that can be suitable for regenerating different tissues such as bone and soft tissues. This paper presents a design of a new hybrid construct in which a polymer (polycaprolactone (PCL)) membrane firmly adheres to a layer of hydrogen (gelatin). MethodsPCL membranes with defined size and porosity were fabricated using 3D printing. The gelatin layer was attached to the PCL membranes using the aminolysis procedure. We have examined this construct for the application of Guided Bone Regeneration (GBR) as a typical surgical regenerative procedure of the oral cavity at the interface of bone and soft tissue. Complete in vitro and in vivo investigations on canine tibia bone defects have been performed. Histological analyses for fibrosis morphometric and bone morphometric evaluation, as well as bone-fibrosis histological grading and CBCT imaging, were conducted. ResultsChemical and morphological studies of the membrane proved that gelatin was uniformly attached to the aminolyzed PCL membranes. The in vitro and in vivo studies indicated the membrane's biocompatibility, mechanical stability, and barrier function for the GBR application. Furthermore, in vitro study showed that the membranes could improve osteogenesis and the regeneration of bone defects. The results illustrated that the mean bone density in the membrane groups was about three times more than that of the control group. SignificanceThe fabricated 3D-printed hybrid Gelatin/PCL bi-layered membrane can be a good candidate for interfacial tissue engineering and a promising membrane for GBR procedure.

Development of Mechanical Stability in Late-Stage Embryonic Erythroid Cells: Insights From Fluorescence Imaged Micro-Deformation Studies.

The combined use of fluorescence labeling and micro-manipulation of red blood cells has proven to be a powerful tool for understanding and characterizing fundamental mechanisms underlying the mechanical behavior of cells. Here we used this approach to study the development of the membrane-associated cytoskeleton (MAS) in primary embryonic erythroid cells. Erythropoiesis comes in two forms in the mammalian embryo, primitive and definitive, characterized by intra- and extra-vascular maturation, respectively. Primitive erythroid precursors in the murine embryo first begin to circulate at embryonic day (E) 8.25 and mature as a semi-synchronous cohort before enucleating between E12.5 and E16.5. Previously, we determined that the major components of the MAS become localized to the membrane between E10.5 and E12.5, and that this localization is associated with an increase in membrane mechanical stability over this same period. The change in mechanical stability was reflected in the creation of MAS-free regions of the membrane at the tips of the projections formed when cells were aspirated into micropipettes. The tendency to form MAS-free regions decreases as primitive erythroid cells continue to mature through E14.5, at least 2 days after all detectable cytoskeletal components are localized to the membrane, indicating continued strengthening of membrane cohesion after membrane localization of cytoskeletal components. Here we demonstrate that the formation of MAS-free regions is the result of a mechanical failure within the MAS, and not the detachment of membrane bilayer from the MAS. Once a “hole” is formed in the MAS, the skeletal network contracts laterally along the aspirated projection to form the MAS-free region. In protein 4.1-null primitive erythroid cells, the tendency to form MAS-free regions is markedly enhanced. Of note, similar MAS-free regions were observed in maturing erythroid cells from human marrow, indicating that similar processes occur in definitive erythroid cells. We conclude that localization of cytoskeletal components to the cell membrane of mammalian erythroid cells during maturation is insufficient by itself to produce a mature MAS, but that subsequent processes are additionally required to strengthen intraskeletal interactions.

Overview of Recent Progress in Studies on Archaeal–Type Artificial Lipid Membranes and Their Applications

Archaeal lipids are attracting the attentions of biologists, biochemists, materials scientists, and bioengineering researchers for many years, due to their unique membrane properties, e.g., low membrane permeability and mechanical stability. In this review, an overview of the recent progress in studies on their membrane properties, clarified with real measurements as well as molecular dynamics simulation techniques, and the applications of archaeal and/or archaeal–type artificial lipids to the biotechnology field, is presented.

Surface Properties of Synaptosomes in the Presence of L-Glutamic and Kainic Acids: In Vitro Alteration of the ATPase and Acetylcholinesterase Activities.

Morphologically and functionally identical to brain synapses, the nerve ending particles synaptosomes are biochemically derived membrane structures responsible for the transmission of neural information. Their surface and mechanical properties, measured in vitro, provide useful information about the functional activity of synapses in the brain in vivo. Glutamate and kainic acid are of particular interest because of their role in brain pathology (including causing seizure, migraine, ischemic stroke, aneurysmal subarachnoid hemorrhage, intracerebral hematoma, traumatic brain injury and stroke). The effects of the excitatory neurotransmitter L-glutamic acid and its agonist kainic acid are tested on Na+, K+-ATPase and Mg2+-ATPase activities in synaptic membranes prepared from the cerebral cortex of rat brain tissue. The surface parameters of synaptosome preparations from the cerebral cortex in the presence of L-glutamic and kainic acids are studied by microelectrophoresis for the first time. The studied neurotransmitters promote a significant increase in the electrophoretic mobility and surface electrical charge of synaptosomes at 1–4 h after isolation. The measured decrease in the bending modulus of model bimolecular membranes composed of monounsaturated lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine provides evidence for softer membranes in the presence of L-glutamate. Kainic acid does not affect membrane mechanical stability even at ten-fold higher concentrations. Both the L-glutamic and kainic acids reduce acetylcholinesterase activity and deviation from the normal functions of neurotransmission in synapses is presumed. The presented results regarding the modulation of the enzyme activity of synaptic membranes and surface properties of synaptosomes are expected by biochemical and biophysical studies to contribute to the elucidation of the molecular mechanisms of neurotransmitters/agonists’ action on membranes.

Investigating the Antibacterial Activity of Polymeric Membranes Fabricated with Aminated Graphene Oxide.

A novel, functionalized graphene oxide–based cellulose acetate membrane was fabricated using the phase inversion method to improve the membrane characteristics and performance. We studied the effect of aminated graphene oxide (NH2–GO) composite on the CA membrane characteristics and performance in terms of membrane chemistry, hydrophilicity, thermal and mechanical stability, permeation flux, and antibacterial activity. The results of contact angle and water flux indicate the improved hydrophilic behavior of composite membranes in comparison to that of the pure CA membrane. The AGO-3 membrane showed the highest water flux of about 153 Lm−2h−1. The addition of hydrophilic AGO additive in CA membranes enhanced the antibacterial activity of AGO–CA membranes, and the thermal stability of the resulting membrane also improved since it increases the Tg value in comparison to that of a pristine CA membrane. The aminated graphene oxide (NH2–GO) was, therefore, found to be a promising additive for the fabrication of composite membranes with potent applications in wastewater treatment.

Intercalation of soft PPy polymeric nanoparticles in graphene oxide membrane for enhancing nanofiltration performances

• PPy particles make GOM with dye adsorption function for sub-nano dyes removement. • Intercalation of PPy improves the GOM’s stability extremely. • PPy nanoparticles modified GOM resulting in 14 times faster water flux. • PPy inhibits the swelling feature of GOM and exhibits improved separation ability. Graphene oxide-based membrane (GOM) has been massively studied in the dye/water separation field, predominately relying on their 1 nm-sized interlayer distance spacing (D-spacing). However, the inefficient removal of sub-nanosized dye molecules and swelling-induced weak long-term stability are currently two key challenges faced by GOM. In this work, we intercalate the soft polymeric polypyrrole (PPy) nanoparticles into GOM to address such gaps. The strong dye adsorption ability of PPy results in the increase of the sub-nanosized MB molecule rejection rate from 60% for GOM to 97% for GO-PPy membrane (GPM) after the initial filtration treatment. Simultaneously, the nanochannels of GPM are partially expanded, leading to an approximately a ~14 times water permeability (21.14 L m -2 h −1 bar −1 ) improvement over GOM (1.56 L m -2 h −1 bar −1 ). More importantly, the strong hydrogen-bond, electrostatic, and π-π interactions between GO and PPy improve the membrane mechanical stability and further reduce the D-spacing, while the enhanced separation ability of nano-sized dye molecules is also exhibited evidenced by the > 99% rejection rates of CV, EBT, CR, and TB. We consider that our strategy could promote the design and development of the high-performance GOM for nanofiltration applications.

Polyether Sulfone-Graphene Oxide- Polyvinyl Pyrrolidone Nanocomposite Adsorptive Membrane for Arsenic Removal from Wastewater

Arsenic contamination poses a major public health concern and harms the environment with its toxicity. Long term exposure to a high concentration of arsenic is harmful to human health as well as the environmental biodiversity. This study is aimed to fabricate and investigate the possibility of polyethersulfone-graphene oxide-polyvinyl pyrrolidone (PES-GO-PVP) nanocomposite adsorptive membrane and use it to enhance the removal of arsenic from wastewater. The nanocomposite membrane in this study was fabricated via the non-solvent induced phase separation (NIPS) method with the addition of polyvinylpyrrolidone (PVP) as a pore-forming agent. Based on the characterization results of GO through Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy, the existence of high quantity of oxygen based functional groups with high degree of oxidation was observed, which indicated that the GO were well-synthesized. The characterization of the membrane indicated that the addition of GO and PVP could impact the membrane hydrophilicity and mechanical stability. Three adsorption parameters (initial concentration of arsenic, pH and contact time) were then optimized using a face-centred central composite design (FCCCD). The arsenic removal efficiency of 88.6 % was obtained with 55 mg/L of initial arsenic concentration, at pH 8 and 75 minutes of contact time between PES-GO-PVP membrane and the arsenic ion. The Langmuir isotherm model fitted the equilibrium data, describing the monolayer adsorption mechanism occurred on the surface of the membrane. Therefore, the results obtained in this study prove the suitability and promising potential of the nanocomposite membrane for effective removal of arsenic through adsorption.

In vitro effects of temperature on red blood cell deformability and membrane stability in human and various vertebrate species.

The effects of temperature on micro-rheological variables have not been completely revealed yet. To investigate micro-rheological effects of heat treatment in human, rat, dog, and porcine blood samples. Red blood cell (RBC) - buffer suspensions were prepared and immersed in a 37, 40, and 43°C heat-controlled water bath for 10 minutes. Deformability, as well as mechanical stability of RBCs were measured in ektacytometer. These tests were also examined in whole blood samples at various temperatures, gradually between 37 and 45°C in the ektacytometer. RBC deformability significantly worsened in the samples treated at 40 and 43°C, more expressed in human, porcine, rat, and in smaller degree in canine samples. The way of heating (incubation vs. ektacytometer temperation) and the composition of the sample (RBC-PBS suspension or whole blood) resulted in the different magnitude of RBC deformability deterioration. Heating affected RBC membrane (mechanical) stability, showing controversial alterations. Significant changes occur in RBC deformability by increasing temperature, showing inter-species differences. The magnitude of alterations is depending on the way of heating and the composition of the sample. The results may contribute to better understanding the micro-rheological deterioration in hyperthermia or fever.

An investigation into the critical tension of electroporation in anionic lipid vesicles.

Irreversible electroporation (IRE) is a technique for the disruption of localized cells or vesicles by a series of short and high-frequency electric pulses which has been used for tissue ablation and treatment in certain diseases. It is well reported that IRE induces lateral tension in the membranes of giant unilamellar vesicles (GUVs). The GUVs are prepared by a mixture of anionic lipid dioleoylphosphatidylglycerol (DOPG) and neutral lipid dioleoylphosphatidylcholine (DOPC) using the natural swelling method. Here the influence of DOPG mole fraction, XDOPG, on the critical tension of electroporation in GUVs has been investigated in sodium chloride-containing PIPES buffer. The critical tension decreases from 9.0 ± 0.3 to 6.0 ± 0.2 mN/m with the increase of XDOPG from 0.0 to 0.60 in the membranes of GUVs. Hence an increase in XDOPG greatly decreases the mechanical stability of membranes. We develop a theoretical equation that fits the XDOPG dependent normalized critical tension, and obtain a binding constant for the lipid-ion interaction of 0.75M-1. The decrease in the energy barrier for formation of the nano-size nascent or prepore state, due to the increase in XDOPG, is the main factor explaining the decrease in critical tension of electroporation in vesicles.

The analysis of dissolved inorganic carbon in liquid using a microfluidic conductivity sensor with membrane separation of CO2

Autonomous continuous analysis of oceanic dissolved inorganic carbon (DIC) concentration with depth is of great significance with regard to ocean acidification and climate change. However, miniaturisation of in situ analysis systems is hampered by the size, cost and power requirements of traditional optical instrumentation. Here, we report a low-cost microfluidic alternative based on CO2 separation and conductance measurements that could lead to integrated lab-on-chip systems for ocean float deployment, or for moored or autonomous surface vehicle applications. Conductimetric determination of concentration, in the seawater range of 1000–3000 µmol kg−1, has been achieved using a microfluidic thin-film electrode conductivity cell and a membrane-based gas exchange cell. Sample acidification released CO2 through the membrane, reacting in a NaOH carrier, later drawn through a sub-µL conductivity cell, for impedance versus time measurements. Precision values (relative standard deviations) were ~ 0.2% for peak height measurements at 2000 µmol kg−1. Comparable precision values of ~ 0.25% were obtained using a C4D electrophoresis headstage with similar measurement volume. The required total sample and reagent volumes were ~ 500 µL for the low volume planar membrane gas exchange cell. In contrast, previous conductivity-based DIC analysis systems required total volumes between 5000 and 10,000 µL. Long membrane tubes and macroscopic wire electrodes were avoided by incorporating a planar membrane (PDMS) in the gas exchange cell, and by sputter deposition of Ti/Au electrodes directly onto a thermoplastic (PMMA) manifold. Future performance improvements will address membrane chemical and mechanical stability, further volume reduction, and component integration into a single manifold.

Влияние ионного состава криопротекторной среды и криоконсервирования на чувствительность эритроцитов человека к механическому стрессу

In this research, we have studied the impact of electrolytes and Ca2+ ions on the development of hemolytic damages in human erythrocytes in cryoprotectant solutions under mechanical stress, as well as the ei¬€ect of freeze-thawing of cells in the presence of glycerol and polyethylene glycol (PEG) on their mechanical stability. The decrease in mechanical stability of cells was found when the salt concentration in extracellular medium increased. At the same time, the absence of electrolytes in cryoprotectant solutions reduced their stability under mechanical stress as well. The Ca2+ introduction into the media increased the cell hemolysis only in the presence of PEG, but not glycerol, apparently due to dii¬€ erent ei¬€ects of these substances on the activity of Ca2+-regulating systems. The introduction of salt of ethylenediaminetetraacetic acid (EDTA) into the media composition reduced the erythrocyte membrane mechanical stability in the presence of the both cryoprotectants, which might be due to the chelator ei¬€ect on membrane-bound Ca2+. Cryopreservation of erythrocytes increased their sensitivity to mechanical stress, and even the cryoprotectant removal could not restore the cell properties up to the control parameters. Probl Cryobiol Cryomed 2019; 29(4): 317-331

Grafting high content of imidazolium polymer brushes on graphene oxide for nanocomposite membranes with enhanced anion transport

Polymer functionalized nanoparticles have attracted burgeoning interests in designing and fabricating novel nanocomposite membranes for fast transport of ions or small molecules. Herein, imidazolium polymer coated graphene oxides (AImGOs), bearing different length of polymer brushes, are synthesized via ATRP technique, and thus a very high weight percentage of imidazolium polymer brushes on GO (up to 89.5%) is acquired, corresponding to a high IEC value up to 65.5 mmol g−1. The as-synthesized AImGOs are then dispersed into poly(vinyl alcohol) (PVA) to prepare nanocomposite membranes. The polymer brushes coated on AImGOs render better interfacial compatibility and filler dispersity. The large specific surface area and high aspect ratio of GO contributes to the enhancement of swelling resistance and mechanical stability of membranes. More importantly, the imidazolium polymer brushes on AImGOs endow the membrane with efficient OH– conduction ability due to the high loading of OH– hopping sites, the flexible chain, and the intrinsic large surface area of GO, demonstrating that efficient OH−-hopping pathways are constructed along the interface between PVA matrix and AImGO. By lengthening the polymer brushes, increasing AImGO content, and adopting appropriate types of imidazolium cations, a remarkable increment of OH– conductivity are observed. To be noted, long polymer brushes quaternized with ethyl chloroformate yield zwitterion type functionality, entitling the highest OH– conductivity of 31.6 mS cm−1 at 30 °C (100% RH).

Gradient crystallinity and its influence on the poly(vinylidene fluoride)/poly(methyl methacrylate) membrane‐derived by immersion precipitation method

ABSTRACTHerein, phase inversion poly(vinylidene fluoride)/poly(methyl methacrylate) (PVDF/PMMA) microporous membranes were prepared at various PMMA concentration by immersion precipitation method. Increment in the PMMA concentration has a significant influence in the PVDF membrane crystallinity, which is studied by differential scanning calorimeter, X‐ray diffractometer, and small‐angle X‐ray scattering analyses. Properties such as membrane bulk structure, porosity, hydrophilicity, mechanical stability, and water flux vary in terms of PMMA concentration. Porosity is increased, and tensile strength decreased when PMMA concentration is beyond 30 wt %. Thermodynamic instability during the liquid to solid phase separation and variation in the crystallinity has an intense effect on these membrane properties. Then, 70/30 blend membrane selected as optimum composition owing to the high porosity and pure water flux compared to other compositions. This membrane is modified with a composite filler derived from the graphene oxide and titanate crosslinked by chitosan. The antibacterial, antifouling, and bovine serum albumin separation studies reveal that the developed nanocomposite membrane is a potential candidate for the separation application. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48677.

Biocompatible Fe3O4@SiO2-NH2 nanocomposite as a green nanofiller embedded in PES-nanofiltration membrane matrix for salts, heavy metal ion and dye removal: Long-term operation and reusability tests.

High purity amorphous silica (95.55%) was simply extracted from rice husk and used as a shell for Fe3O4 magnetic nanoparticles. The obtained eco-friendly nanomaterial was functionalized by (3-Aminopropyl)trimethoxysilane and characterized by SEM, FT-IR, XRD, VSM, TEM and zeta potential analyses. The synthesized Fe3O4@SiO2-NH2 nanocomposite was embedded into the polyethersulfone membranes with different concentrations via phase inversion method. The effects of Fe3O4@SiO2-NH2 on various properties of the prepared nanofiltration membranes including membrane morphology, hydrophilicity, porosity, and mechanical stability were investigated using SEM image, water contact angle test, porosity measurement and mechanical property analysis, respectively. The performance of Fe3O4@SiO2-NH2 nanocomposite modified membranes was evaluated by measuring the pure water flux, salts rejection, Cd(II) ions removal, MR dye retention, and antifouling property. The results showed that the pure water flux was significantly increased in Fe3O4@SiO2-NH2 modified membranes due to the presence of hydrophilic functional groups on the Fe3O4@SiO2-NH2 surface. In addition, the significant enhancement in efficiency of modified membranes for removal of Cd(II) ions and MR dye was observed due to the adsorption properties of Fe3O4@SiO2-NH2 nanocomposite. Among the modified membranes with different concentrations of Fe3O4@SiO2-NH2, the 0.5 wt% concentration of nanocomposite showed the highest efficiency for the removal of Cd(II) ions (93%) and MR dye (97%). Membrane reusability study indicated a slightly decrease (≈7%) in Cd(II) ions removal after five continuous cycles. Membrane long-term filtration study showed a little reduction in permeate flux with unchanged MR dye retention during long-term filtration, which confirmed the stability of modified membrane.