Polymer Membrane Surface Research Articles

Hydrophilic modification of polypropylene ultrafiltration membrane by air‐assisted polydopamine coating

Coating by a mussel inspired polydopamine (PDA) is a simple and promising strategy to modify the hydrophilicity of polymer membrane surfaces. In this work, PDA coating was used to modify polypropylene (PP) ultrafiltration hollow fiber membrane. PDA coating parameters, ie, solution concentration and coating time were varied, and the effect of those parameters on membrane morphology, porosity, water contact angle, and pure water flux was investigated. In addition, air‐assisted PDA coating process was also conducted by channelling the air through PP membrane to avoid pore blocking and prevent water flux decline. The results showed that PDA coating successfully improved the hydrophilicity of PP membrane indicated by the decrease of water contact angle from 110° to 67° after coated by 3 g/L of PDA solution for 3 hours. The addition of air permeation on membrane lumen also increased pure water flux up to 511.2 L/m2.h, a 270% increase from unmodified PP membrane. It might be associated to the pore blocking prevention that has been proven by SEM image and the membrane porosity that was increased about 4%.

Polymer Membranes Dispersed Liquid Crystal (PMDLC): a new electro-optical device

ABSTRACTPolymer Dispersed Liquid Crystals (PDLCs) are liquid crystal dispersions in a polymer matrix, which look like opaque in their OFF state, when no electric field is applied, and transparent in their ON state. They are generally obtained by a phase separation process, such as Thermal, Solvent- and Polymerization-Induced Phase Separation (TIPS, SIPS and PIPS, respectively), between two transparent conductive glass substrates. In this paper, a new electro-optical device, formed by a porous polymer membrane imbibed with liquid crystal by capillary suction, is presented (Polymer Membranes Dispersed Liquid Crystals, PMDLC). Polymer membrane surfaces were made conductive before liquid crystal loading by magnetron sputtering of a thin layer of conductive indium tin oxide. The morphology and the electro-optical response of these devices were investigated and the observed transmittances and relaxation times were found to be similar to those of conventional PDLCs. In addition, PMDLCs showed interesting flexibility as no solid conductive substrate is required and economic convenience as there is no loss of liquid crystal in the polymer matrix.

Лазерная фотолюминесцентная спектроскопия приповерхностной микроструктуры полимерной мембраны "Нафион" в дейтерированной воде

The paper describes experiments in exposing the surface of a water-swollen Nafion polymer membrane to near ultraviolet radiation at grazing incidence. Ultraviolet radiation caused the surface of the Nafion polymer membrane to photoluminesce in a specific spectral range. This luminescence appears due to the presence of sulphonic acid groups at the ends of perfluorovinyl ether groups that form the polytetrafluoroethylen base of the Nafion membrane. We show that the photoluminescence signal is an important parameter for describing the process of polymer swelling in water

【Original Contribution】Molecular Simulation of Adsorption Behavior of a Silica Nanoparticle onto a Polymeric Membrane Surface in Water

【Original Contribution】Molecular Simulation of Adsorption Behavior of a Silica Nanoparticle onto a Polymeric Membrane Surface in Water

Surface modification of polymeric flat sheet membranes by adding oligomeric fluoroalcohol

Abstract The present study attempted to modify the surface of polymeric membranes by mixing 2-(perfluoroalkyl)ethanol with polyethersulfone to improve the hydrophobicity of the membrane. The characteristics of the surface-modified membrane were examined by using the contact angle, liquid entry pressure (LEPw), X-ray photoelectron spectroscopy spectra, and scanning electron microscopy measurements. The modified membrane was tested for SO2 absorption. The surface contact angle and LEPw values increased by the addition of fluoroalcohol. The fluorine/carbon atomic ratio decreased with increasing evaporation period. The modified membrane was utilized for the absorption of SO2 from the simulated flue gas in alkaline medium (0.5 m NaOH solution). The SO2 removal efficiency slightly decreased probably due to the transformation of the finger-like structure into a sponge-like structure, and the increase in the membrane resistance. The SO2 absorption rate also increased as the gas flow rate increased.

Surface modification of polyvinylidene fluoride membrane by atom-transfer radical-polymerization of quaternary ammonium compound for mitigating biofouling

Fabrication of antibiofouling membrane is a vital but challenging task for the treatment of water and wastewater using membrane-based processes. In this work, quaternary ammonium compounds (QACs) were grafted onto polyvinylidene fluoride (PVDF) membrane via surface-initiated activators regenerated by electron transfer atom-transfer radical-polymerization (ARGET ATRP) method. Membrane surface characterization demonstrated that QAC was successfully grafted onto the PVDF membrane surface. The QAC-modified membrane (MQ) demonstrated prominent antimicrobial capability by destruction of cell integrity, with an inhibition rate ~98.3% of E. coli and ~98.5% of S. aureus, respectively. Batch filtration tests showed that MQ membrane had lower flux decline rate compared to control membrane (M0) under constant-pressure filtration. Confocal laser scanning microscopy analysis revealed that less total cells and more dead cells were present on MQ membrane compared to M0. The quantity of polysaccharides and proteins on MQ membrane was reduced as well. The grafted QAC on PVDF membrane also showed favorable stability during repeated fouling-cleaning tests. These results highlight that the ARGET ATRP method for grafting QAC onto polymeric membrane surface is a robust way to fabricate low-biofouling membrane for water and wastewater treatment.

New Image Texture Analysis, and Application to Polymer Membrane Surface Morphologies and Roughness.

A new method of image texture analysis is presented, based on the mean and standard deviation of gray levels within domains in an image. The calculations are performed recursively on domains of various sizes within the images. These gray level calculations are used as the input matrix for principal component analysis. The technique analyzes the entire image as a whole and is not for image segmentation. The analysis routine operates across all distances, frequencies and directions in the image, and is not computationally burdensome. The method was applied to scanning electron microscope images of reverse osmosis membranes on domains from 23 nm to 3 µm. The texture analysis technique performed well in identifying the surface morphology and, once calibrated, in predicting the surface roughness as measured by atomic force microscopy.

Crude-Oil-Repellent Membranes by Atomic Layer Deposition: Oxide Interface Engineering.

Crude oil fouling on membrane surfaces is a persistent, crippling challenge in oil spill remediation and oilfield wastewater treatment. In this research, we present how a nanosized oxide coating can profoundly affect the anti-crude-oil property of membrane materials. Select oxide coatings with a thickness of ∼10 nm are deposited conformally on common polymer membrane surfaces by atomic layer deposition to significantly mitigate fouling during filtration processes. TiO2- and SnO2-coated membranes exhibited far greater anti-crude-oil performance than ZnO- and Al2O3-coated ones. Tightly bound hydration layers play a crucial role in protecting the surface from crude oil adhesion, as revealed by molecular dynamics simulations. This work provides a facile strategy to fabricate crude-oil-resistant membranes with negligible impact on membrane structure, and also demonstrates that, contrary to common belief, excellent crude oil resistance can be achieved easily without implementation of sophisticated, hierarchical structures.

Relationship between Energy Characteristics of Surface of Polymeric Membranes and Their Transport Properties

Molecular theory of wetting was used to calculate the specific free surface energy of membranes based on amorphous polymers of varied chemical structure from experimental wetting angles obtained for test fluids. A relationship was found between the dispersion component of the surface energy of a membrane, its gas permeability, and free volume of the polymer. This makes it possible to employ the wetting method to prognosticate the transport properties of polymeric membranes. In wetting of membranes with aqueous solutions of alcohols, the concentration of an alcohol corresponding to the onset of its sorption into the membrane was determined. The correlation of the value obtained with the alcohol concentration that corresponds to the onset of sorption and is determined independently by the gravimetric method enables use of wetting angles for optimizing the conditions of experiments on nanofiltration and pervaporation.

Continuous purification of active pharmaceutical ingredients utilizing polymer membrane surface wettability.

Continuous processing of pharmaceuticals opens opportunities for continuous separation based on wettability of polymer membranes. Dual use of hydrophobic and hydrophilic membranes realize in-line liquid-liquid extraction in the synthesis of four essential APIs. A secondary membrane with opposite wetting characteristics proves critical to phase separation of aqueous-organic reaction streams.

Ionic liquid mediated surface micropatterning of polymer blends

ABSTRACTA polymer of intrinsic porosity (i.e., PIM‐1) has been blended with different ionic liquids (ILs) in order to evaluate the effect of the ILs on the microstructure of the polymer blend. [C8MIM][Cl], [BMIM][DCa], [BMPyr][DCa], and [BMIM][Tf2N] have been selected and were mixed with PIM‐1. Polymer blends containing up to 80 wt % of ILs were prepared by a casting method with chloroform as solvent. SEM images show that during the film formation a structuring of the surface appears depending on the nature and the concentration of ILs, with appearance of well‐defined microstructure in the case of [BMIM][Tf2N] and [BMIM][DCa]. In the case of [BMIM][Tf2N]/PIM‐1 film, the lower IL concentration induces the denser film with small micropatterns onto the surface. AFM analysis indicates that the ILs are well dispersed on the surface. X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and water contact angle measurements show that a gradient of IL concentration is observed across the film thickness. It is demonstrated that ILs are versatile co‐solvents for inducing controlled micropatterns in polymer membrane surfaces. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46109.

Plasma modification of microporous polymer membranes for application in biomimetic dissolution studies

Biorelevant dissolution is an indispensable tool utilized during formulation development and optimization for the prediction of in vivo bioavailability of pharmaceutical agents. Within that framework, membrane-permeation dissolution methodologies are widely used to model drug absorption. The current work evaluates polymer membrane surface modifications for production of biomimetic membranes to be employed in biorelevant dissolution studies. Biomimetic membranes exhibit hydrophilic and hydrophobic properties to simulate the intestinal membrane environment. Low temperature plasma treatment of microporous polyethersulfone (PES), nylon and polypropylene (PP) polymer membranes was applied to produce low energy surface layers with permanent hydrophobic and hydrophilic functionalities. Surface modifications on microporous polymer membranes were achieved by plasma treatments using tetrafluoromethane (CF4), perfluorohexane (C6F14), dichloromethane (DCM) and water (H2O). Surface characterization of treated membranes was evaluated using scanning electron microscopy energy dispersive x-ray spectroscopy (SEM-EDS), water contact angle (CA) and x-ray photoelectron spectroscopy (XPS) techniques. SEM-EDS analysis of polymer membranes treated with fluorinated and chlorinated solvents/gases depicts altered surface morphologies with enriched porosity. SEM-EDS and XPS analyses demonstrate the chemical modification at the surface of treated membranes is strongly influenced by the type of treatment gas or solvent. Results show fluorination as a more effective and less destructive treatment technique. XPS confirmed the presence of elemental fluorine functional groups at the surface of the PES and nylon membranes. Evaluating elemental changes (F/C ratio) from multiple techniques confirms fluorinated plasma treatments are localized to the surface of the membrane and do not significantly affect the bulk properties. In a supplemental study, a detailed comparison of the plasma treated polymer membranes and porcine intestines revealed the biomimetic nature of the modified membranes.

Integrating zwitterionic polymer and Ag nanoparticles on polymeric membrane surface to prepare antifouling and bactericidal surface via Schiff-based layer-by-layer assembly

Development of antibacterial membranes is strongly desired for biomedical applications. Herein, we integrated antifouling and bactericidal properties on polymeric membrane surface via Schiff-based layer-by-layer (LbL) assembly. Zwitterionic polymers bearing plentiful amino groups (based on polyethylenimine (PEI) and sulfobetaine methacrylate (SBMA), and termed as PEI-SBMA) were utilized to prepare an antifouling membrane surface; then robust wide-spectrum bactericidal Ag nanoparticles (Ag NPs) were in situ generated on the surface. The as-prepared zwitterionic polymer surface showed excellent resistance to protein adsorption and bacterial adhesion. The Ag NPs could be tightly and uniformly distributed on the membrane surface by the chelation of PEI-SBMA, and endowed the membrane with bactericidal activity. Meanwhile, the Ag NPs loaded membrane could effectively resist bacterial attachment for a long time, even though the bactericidal activity lost. The proposed bactericidal and antifouling membrane was flexible, versatile and could be large-scale preparation; and this strategy would have great potential to be widely used to avoid undesired bacterial contamination of biomedical implants or biological devices.

Modified membrane with antibacterial properties

Bacteria have been considered as a major foulant that initiates the formation of biofilm on the polymeric membrane surface. Some polymeric membranes are naturally antibacterial and have low fouling properties, however, numerous efforts have been devoted to improve their antibacterial performance. These modifications are mostly carried out through blending the membrane with an antibacterial agent or introducing the antibacterial agent on the membrane surface by chemical grafting. Currently, a significant number of researches have reported nanocomposite membrane as a new approach to fabricate an excellent antibacterial membrane. The antibacterial nanoparticles are dispersed homogenously in membrane structure by blending method or coating onto the membrane surface. Aim of the modifications is to prevent the initial attachment of bacteria to membrane surface and kill bacteria when attached on the membrane surface. In this paper, several studies on antibacterial modified membranes, particularly for water treatment, will be reviewed comprehensively. Special attention will be given on polymeric membrane modifications by introducing antibacterial agents through different methods, such as blending, grafting, and coating.

Mussel-Inspired Architecture of High-Flux Loose Nanofiltration Membrane Functionalized with Antibacterial Reduced Graphene Oxide-Copper Nanocomposites.

Graphene-based nanocomposites have a vast potential for wide-ranging antibacterial applications due to the inherently strong biocidal activity and versatile compatibility of such nanocomposites. Therefore, graphene-based functional nanomaterials can introduce enhanced antibiofouling and antimicrobial properties to polymeric membrane surfaces. In this study, reduced graphene oxide-copper (rGOC) nanocomposites were synthesized as newly robust biocides via in situ reduction. Inspired by the emerging method of bridging ultrafiltration membrane surface cavities, loose nanofiltration (NF) membranes were designed using a rapid (2 h) bioinspired strategy in which rGOC nanocomposites were firmly codeposited with polydopamine (PDA) onto an ultrafiltration support. A series of analyses (SEM, EDS, XRD, XPS, TEM, and AFM) confirmed the successful synthesis of the rGO-Cu nanocomposites. The secure loading of rGOC composites onto the membrane surfaces was also confirmed by SEM and AFM images. Water contact angle results display a high surface hydrophilicity of the modified membranes. The PDA-rGOC functionalization layer facilitated a high water permeability (22.8 L m-2 h-1 bar-1). The PDA-rGOC modification additionally furnished the membrane with superior separation properties advantageous for various NF applications such as dye purification or desalination, as ultrahigh (99.4% for 0.5 g L-1 reactive blue 2) dye retention and high salt permeation (7.4% for 1.0 g L-1 Na2SO4, 2.5% for 1.0 g L-1 NaCl) was achieved by the PDA-rGOC-modified membranes. Furthermore, after 3 h of contact with Escherichia coli (E. coli) bacteria, the rGOC-functionalized membranes exhibited a strong antibacterial performance with a 97.9% reduction in the number of live E. coli. This study highlights the use of rGOC composites for devising loose NF membranes with strong antibacterial and separation performance.

The effect of polymeric membrane surface on HaCaT cell properties

The control of the surface properties is an important issue for applicability of polymer membranes interacting with cells. In this work, the influence of surface roughness and stiffness of two polymer membranes on viability and mechanical properties of keratinocytes was studied. Terpolimer polyglicolide, polycaprolactone and polylactide, (PGA-PCL-PLA) and copolymer polycaprolactone, polyglicolide (PGA-PCL) substrates were used for membranes fabrication. Surface modification – the hydrolysis of the obtained membranes was carried out. The analysis of membranes’ surface properties revealed that RMS surface roughness and roughness factor of PGA-PCL-PLA membrane decreased after hydrolysis while its stiffness increased. In contrast, the PGA-PCL membrane stiffness was only slightly affected by NaOH treatment. Immortalized human keratinocytes (HaCaT) were grown under standard conditions on the surface of the studied membranes and characterized by means of atomic force microscopy and fluorescence microcopy. The results showed the substrate-dependent effect on cells’ properties.

New insights into the effects of biomaterial chemistry and topography on the morphology of kidney epithelial cells

Increasing incidence of renal pathology in the western world calls for innovative research for the development of cell-based therapies such as a bioartificial kidney (BAK) device. To fulfil the multitude of kidney functions, the core component of the BAK is a living membrane consisting of a tight kidney cell monolayer with preserved functional organic ion transporters cultured on a polymeric membrane surface. This membrane, on one side, is in contact with blood and therefore should have excellent blood compatibility, whereas the other side should facilitate functional monolayer formation. This work investigated the effect of membrane chemistry and surface topography on kidney epithelial cells to improve the formation of a functional monolayer. To achieve this, microtopographies were fabricated with high resolution and reproducibility on polystyrene films and on polyethersulfone-polyvinyl pyrrolidone (PES-PVP) porous membranes. A conditionally immortalized proximal tubule epithelial cell line (ciPTEC) was cultured on both, and subsequently, the cell morphology and monolayer formation were assessed. Our results showed that L-dopamine coating of the PES-PVP was sufficient to support ciPTEC monolayer formation. The polystyrene topographies with large features were able to align the cells in various patterns without significantly disruption of monolayer formation; however, the PES-PVP topographies with large features disrupted the monolayer. In contrast, the PES-PVP membranes with small features and with large spacing supported well the ciPTEC monolayer formation. In addition, the topographical PES-PVP membranes were compatible as a substrate membrane to measure organic cation transporter activity in Transwell® systems. Copyright © 2016 John Wiley & Sons, Ltd.

Dopamine-induced nonionic polymer coatings for significantly enhancing separation and antifouling properties of polymer membranes: Codeposition versus sequential deposition

Nonionic polymers (i.e., poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA), poly(N-vinyl pyrrolidone) (PVP), and poly(N-acryoyl morpholine) (PACMO)) have been reported as promising antifouling materials for membrane surface modification. Better understanding of similarity and difference for the nonionic polymers in terms of hydration capability and antifouling property will benefit the design and development of antifouling surfaces. Herein, two simple and scalable methods yielded composite coatings on the hydrophobic polymer membrane surfaces: (i) a codeposition of polydopamine (PDA) with PEG (or PVA) (labeled as MPDA-PEG and MPDA-PVA), and (ii) a sequential deposition featuring dopamine polymerization followed by the self-assembly of PVP (or PACMO) (labeled as MPDA-PVP and MPDA-PACMO) via hydrogen-bonded interactions. The results suggested that hydrophilicity and surface free energy of all modified membranes were significantly enhanced after introducing PDA and nonionic polymers. The order of improved initial water flux of these modified membranes was MPDA-PEG > MPDA-PVP ≈ MPDA-PVA > MPDA-PACMO. It was appeared that the codeposited membranes (MPDA-PEG and MPDA-PVA membrane) with excellent hydration capability and permeability had better antifouling property. However, antifouling property and durability were remarked for the sequentially deposited membranes (MPDA-PVP and MPDA-PACMO membrane) in comparison to the codeposited membranes as evaluated in protein filtration, oil/water emulsion filtration, and humic acid filtration. The hydration capability of hydrogen-bonded PDA-PVP (or PDA-PACMO) coating endows the sequentially deposited membranes with robust and comprehensive performance. This work systematically demonstrates that coating architecture is a vital role in the design of the nonionic polymer modified membranes.

Low Pressure DC-Plasma System for the Modification of Polymeric Membrane Surfaces

The main objectives of this work were to develop a lab-scale direct current (DC) glow discharges plasma system for modification of organic and inorganic membranes. Characteristics of plasma system were presented under the discharge of five gases (Ar, N2, air, O2, and CO2). A Langmuir double probe was used for the evaluation of the electron temperature (Te) and electron density (ne) of plasmas. The current and voltage (I-V) characteristic curves were analyzed. Relationships between breakdown voltage (VB) of gases and products of gas pressure and inter-electrode gap (pd) were studied in form of Paschen curves. The results showed that Te of plasma in various gases was in the range of 4-13 eV, while the ne varied between 108 and 109 cm-3. The plasma generated at different gas pressure and applied voltage is in the normal and abnormal modes. Finally, the constructed DC-plasma system was utilized for modification of polymeric membrane surfaces. Treatment time, discharge power and type of gas were varied. The tailoring of membrane surfaces was analyzed through the water contact angle and percent-weight loss (PWL) measurements, DMTA, AFM, XPS and FTIR spectrum. It could be shown that DC-plasma from this system can be used to modify the surface of polymeric membranes.

A effective approach for surface modification of polymer membrane via SI-eATRP in an electrochemical cell with a three electrode system

In this study, an environmentally friendly approach for surface modification of polymer membrane was reported, which named surface-initiated electrochemically mediated atom transfer radical polymerization (SI-eATRP). It was triggered after diffusion of a CuI/L activator generated at a working electrode. The introduction of electrochemically mediation can control the polymerization of monomers by a one-electron reduction of an initially added air-stable CuII salt. The reaction was carried out in an electrochemical cell with a three-electrode system at low temperature. Using this technique, hydrophilic polymer brushes of poly(N-vinylpyrrolidone) were grafted onto PES membrane surface. The effects of reaction conditions like polymerization time, monomer concentration, initiator amount, and different monomer on the polymerizations of monomer were investigated in detail. Based on these data, we concluded that the polymerization on polymer membrane surface could be controlled by mediating the reaction condition. Moreover, the precisely controlled polymerization may allow it to serve as excellent model systems for polymer membrane modification, in general, to illustrate the role of electrochemically mediating on the polymerization approach. And the water contact angle of the modified membrane decreased from 89° to 72°. The APTT of the modified membrane increased from 46s to 81s. Those results indicated that the surface modification by grafting PVP brushes provided practical application for the PES membranes with high surface properties.