Multilayer Membranes Research Articles

Multifunctional electromagnetic interference shielding films comprised of multilayered thermoplastic polyurethane membrane and silver nanowire

A well-designed multilayered composite film with alternating thermoplastic polyurethane (TPU) nanofiber membranes and silver nanowire (AgNW) layers was fabricated by vacuum-assisted filtration. The continuous AgNW conductive layer and the sandwich structure facilitated electron transmission efficiency and electromagnetic (EM) wave dissipation through multiple reflections and resonance effect, which resulted in a high electromagnetic interference (EMI) shielding effectiveness (SE) of 97.3 dB mainly attributed to the improvement of SEA. In addition, the surface plasmon resonance of AgNWs endowed the multilayered film excellent photo-thermal property that allowed the rapid increase of surface temperature to 78.0 °C within 100 s under 300 mW/cm2 sun irradiation. The multilayered film displayed excellent triboelectric energy generation ability when pressed using structured polydimethylsiloxane (PDMS) film, which generated high output voltage and current of 225 V and 21.3 μA, respectively. This work provides a promising solution for designing multifunctional films for efficient EMI shielding of wearable electronics.

Discerning perturbed assembly of lipids in a model membrane in presence of violacein

Violacein is a naturally found pigment that is used by some gram negative bacteria to defend themselves from various gram positive bacteria. As a result, this molecule has caught attention for its potential biomedical applications and has already shown promising outcomes as an antiviral, an antibacterial, and an anti-tumor agent. Understanding the interaction of this molecule with a cellular membrane is an essential step to extend its use in the pharmaceutical paradigm. Here, the interaction of violacein with a lipid monolayer formed at the air–water interface is found to depend on electrostatic nature of lipids. In presence of violacein, the two dimensional (2D) pressure–area isotherms of lipids have exhibited changes in their phase transition pressure and in-plane elasticity. To gain insights into the out-of-plane structural organization of lipids in a membrane, X-ray reflectivity (XRR) study on a solid supported lipid monolayer on a hydrophilic substrate has been performed. It has revealed that the increase in membrane thickness is more pronounced in the zwitterionic and positively charged lipids compared to the negatively charged one. Further, the lipid molecules are observed to decrease their tilt angle made with the normal of lipid membrane along with an alteration in their in-plane ordering. This has been quantified by grazing incidence X-ray diffraction (GIXD) experiments on the multilayer membrane formed in an environment with controlled humidity. The structural reorganization of lipid molecules in presence of violacein can be utilized to provide a detailed mechanism of the interaction of this molecule with cellular membrane.

Engineering multilayered MXene/electrospun poly(lactic acid) membrane with increscent electromagnetic interference (EMI) shielding for integrated Joule heating and energy generating

Proliferous bloom of wearable electronics arouses higher demands on electromagnetic pollution defense and multifunctional trait. Yet the EMI shielding materials capable of versatility still remains a challenge. Herein, the multilayered MXene/PLA composite membrane was designed with increscent EMI shielding by alternately assembling MXene onto electrospun poly(lactic acid) (PLA) nanofiber mats. Attributing to the intact conduction of MXene layer and the multiple-reflection-absorption effect, the multilayered membrane achieved an optimum shielding efficiency (SE) of 55.4 dB. The predominant conductivity of MXene rendered the multilayered membrane remarkable Joule heating performance with a rapid temperature response from 31 °C to 52.8 °C within 25s at a low trigger voltage of 1.5 V. The triboelectric nanogenerator (TENG) based on the multilayered membrane exhibited outstanding energy generation with a peak power density of 457.1 mW/m2. This work provides a feasible pathway to prepare high-performance bio-based EMI shielding membranes and gives insights into the design of highly integrated multifunctional devices.

Novel fibrin functionalized multilayered electrospun nanofiber membrane for burn wound treatment

In this study, a novel hybrid multilayered electrospun nanocomposite membrane (MENM) was developed for activated wound dressing applications. An established electrospinning process was employed to fabricate a tri-layer nanocomposite membrane where the lower layer was composed of chitosan (CS)/polyvinyl alcohol (PVA) and fibrin (having regeneration of tissues and bleeding resistance properties), both of which are directly in contact with the burn wound (BW) skin, and a middle layer of PVA/sodium alginate (SA) (having antibacterial properties). The top layer consisted of gelatin (super hydrophilic properties). The MENM morphology was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) which confirmed the presence of the elemental and chemical structures of MENM. The MENM was identified by Fourier transform infrared spectroscopy (FTIR) with a maximum drug release which was ascended within 10-h duration. X-ray diffraction (XRD) showed long-term absorbency due to the presence of more amorphous and less crystallinity percentages in the MENM. The nanocomposites' thermal stability was also observed via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The developed MENM has shown excellent antibacterial activity with a zone of inhibition of 18.7 ± 0.9 mm, 18.9 ± 0.9 mm, 20.0 ± 1 mm and 19.3 ± 0.9 mm, respectively, against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria. The high water absorbant properties of MENM indicate that the produced membranes could absorb the maximum exudate from wounded skin within the shortest time and assist in healing the wound quickly. The produced MENMs could be potential wound dressing materials in the future.

Effect of Asymmetric Membrane Structure on Hydrogen Transport Resistance and Performance of a Catalytic Membrane Reactor for Ethanol Steam Reforming.

The performance of catalytic membrane reactors (CMRs) depends on the specific details of interactions at different levels between catalytic and separation parts. A clear understanding of decisive factors affecting their operational parameters can be provided via mathematical simulations. In the present paper, main results of numerical studies of ethanol steam reforming, followed by downstream hydrogen permeation through an asymmetric supported membrane, are reported. The membrane module consists of a thin selective layer supported on a substrate with graded porous structure. One-dimensional isothermal reaction–transport model for the CMR has been developed, and its validation has been carried out by using performance data from a lab-scale reactor with a disk-shaped membrane. Simulations demonstrate the model’s capabilities to analyze local concentrations gradients, as required to provide accurate estimates of the relationship between structure–property–performance. It was shown that transport properties of multilayer asymmetric membranes are highly related to the structural properties of each single layer.

Nanocomposite Membrane Scaffolds for Cell Function Maintaining for Biomedical Purposes.

Nanocomposite multilayered membrane coatings have been widely used experimentally to enhance biomedical materials surfaces. By the selection of reliable components, such systems are functionalized to be adjusted to specific purposes. As metal nanoparticles can reduce bacterial cell adhesion, the idea of using gold and silver nanoparticles of unique antimicrobial properties within membrane structure is outstandingly interesting considering dressings facilitating wound healing. The study was aimed to explore the interface between eukaryotic cells and wound dressing materials containing various nanoelements. The proposed systems are based on polyethyleneimine and hydroxyapatite thin layers incorporating metallic nanoparticles (silver or gold). To examine the structure of designed materials scanning electron and transmission electron microscopies were applied. Moreover, Fourier-transform infrared and energy-dispersive X-ray spectroscopies were used. Additionally, water contact angles of the designed membranes and their transport properties were estimated. The functioning of human fibroblasts was examined via flow cytometry to assess the biocompatibility of developed shells in the aspect of their cytotoxicity. The results indicated that designed nanocomposite membrane scaffolds support eukaryotic cells’ functioning, confirming that the elaborated systems might be recommended as wound healing materials.

Detection of bromate in packaged drinking water and its removal using polyelectrolyte multilayer membranes

AbstractThe use of bottled water is increasing every day even after the reported presence of microbial and other contaminants. The present study analyzed bromate in bottled water samples collected from four major cities in Kerala, India. It was found that about 40% of the samples contain bromate with a maximum concentration of 9.68 μg/L with an average of 1.56 μg/L. The study also includes the development of a multilayer membrane for the removal of bromate from water. Bilayers of quaternary chitosan salt (QCS)/sodium polystyrene sulfonate (PSS) were deposited on polyethersulfone (PES) microfiltration membrane and which are employed for bromate removal studies. Deposition of six bilayers of QCS/PSS increased the rejection efficiency from ∼4% to ∼84%. The influence of different fabrication and feed parameters on bromate removal efficiency was also studied. Six bilayers of QCS/PSS deposited at pH 2 with 0.5 M NaCl were found to be effective in removing > 90% of bromate from marketed bottled water samples with low energy expense. This study is recommended to implement such a multilayer system as a polishing step in the final stage of water purification in bottling plants to avoid possible contamination and toxicity of bromate in bottled water users.

Optical modeling of cellulose nanofibril self-assembled thin film with iridescence

Nanostructure-induced structural coloration and bio-invisibility are important for camouflaging as it displays color and can be tuned and imparted in a more environmentally friendly manner. However, even though many new camouflage fabrics and technologies are invented, there is a lack of numerical electromagnetic and optical approaches to analyze the phenomenon of light scattering of camouflaging materials from nanostructures. In this study, we built and presented a successful simulation of physical coloration caused by multilayer membrane interference. We created this model based on surfactant-like cellulose nanofibrils (CNFs) that tightly stacked into photon-active microstructure and surface topology for light reflection, thus affecting the film gloss. Incident light coming at a defined wavelength or angle was studied. The effects of film height, high microstructure, and curvature on the optical properties of ITO/PET substrates were investigated. These showed the coloration is highly dependent on the nanostructure’s characteristics. This study provides a general prediction model to deal with optical multilayer systems where interference plays a vital role in optical camouflaging, etc.

Molecular insights into desalination performance of lamellar graphene membranes: Significant of hydrophobicity and interlayer spacing

The multilayer graphene-based membranes have shown well prospect in seawater desalination application owing to their well-defined 2D for rapid water penetration and excellent ion rejection. In this work, the lamellar GRA-X membranes with different hydrophilicity were constructed by stacking functional graphene sheets layer-by-layer. The effect of interlayer spacing and the hydrophilicity of membranes on desalination performance was discussed. The relationship between the hydrophilicity of GRA-X membranes and water flux was also explored by non-equilibrium molecular dynamics simulations (NEMD). It was found that the water flux in GRA-X membranes increased with the decrease hydrophilicity of graphene membrane, and it could be regulated by adjusting the interaction between water molecules and functional groups or controlling the order of water molecules in the pore channels. The rejection rate was mainly determined by the effective distance of interlayer spacing in GRA-X membranes.

Thermal and Vibration Mechanical Reliability of Multicoat Compound Thin-Film Thermocouple

For the thin-film thermocouple with ITO/In2O3 as the functional layer, the mechanical reliability of their composite multilayer membrane structures under high temperature and random vibration conditions are discussed. Using the elastic plasticity model based on the finite element simulation method, the stress and strain distribution patterns caused by the thermal mismatch and vibration of multilayer film materials are systematically analyzed, and the distribution of the stress concentration and strain accumulation regions that may lead to fatal reliability problems are characterized. When a thermal load of 1000 °C is applied, the protective layer of the structure is vulnerable to severe stress environment. In addition, plastic deformation occurs in the adjacent layers of the functional layer, making it a weak reliability area. The stress generated by the vibration load is much smaller than the thermal stress, which mainly occurs at the roots of the structure, where prolonged loading may lead to fatigue failure.

Manufacture of Multilayered Artificial Cell Membranes through Sequential Bilayer Deposition on Emulsion Templates.

Efforts to manufacture artificial cells that replicate the architectures, processes and behaviours of biological cells are rapidly increasing. Perhaps the most commonly reconstructed cellular structure is the membrane, through the use of unilamellar vesicles as models. However, many cellular membranes, including bacterial double membranes, nuclear envelopes, and organelle membranes, are multilamellar. Due to a lack of technologies available for their controlled construction, multilayered membranes are not part of the repertoire of cell‐mimetic motifs used in bottom‐up synthetic biology. To address this, we developed emulsion‐based technologies that allow cell‐sized multilayered vesicles to be produced layer‐by‐layer, with compositional control over each layer, thus enabling studies that would otherwise remain inaccessible. We discovered that bending rigidities scale with the number of layers and demonstrate inter‐bilayer registration between coexisting liquid–liquid domains. These technologies will contribute to the exploitation of multilayered membrane structures, paving the way for incorporating protein complexes that span multiple bilayers.

Release behaviors and kinetics of coated bead‐on‐string nanofibrous multilayer membranes loaded with drug particles

AbstractA bead‐on‐string structure with special beads at the microscale level could act as an effective carrier for solid drug particles as well as giving a continuous and sustained release profile. Tetracycline hydrochloride (TCH), used as solid model drug particles, was ground to obtain nanoscale and well‐distributed size. Electrospun poly[lactic‐co‐(glycolic acid)] (PLGA) bead‐on‐string nanofibers loaded with TCH of different particle sizes were fabricated for controlled drug delivery. The morphology of TCH particles and bead‐on‐string nanofibers were observed using a particle sizer and scanning electron microscopy. The effects of drug particle size on the release behaviors of nanofibers were further investigated and analyzed using UV–visible spectrophotometry. In vitro release results suggested that bead‐on‐string nanofibers encapsulating ground TCH particles had higher total drug release quantity compared with unground particle‐loaded nanofibers. Coating of the surface of PLGA/TCH nanofibers was investigated for controlled‐release effects and the release mechanism to understand the drug–polymer carrier interaction. The results indicated that coating on both sides of nanofibrous membranes could effectively decrease the initial burst release. Bead‐on‐string nanofibers proved to be promising mats for drug delivery applications. © 2021 Society of Industrial Chemistry.

On the performance of multilayered membrane filters

Multilayered membrane filters, which consist of a stack of thin porous membranes with different properties (such as pore size and void fraction), are widely used in industrial applications to remove contaminants and undesired impurities (particles) from a solvent. It has been experimentally observed that the performance of well-designed multilayer structured membranes is markedly better than that of equivalent homogeneous membranes. Mathematical characterization and modeling of multilayered membranes can help our understanding of how the properties of each layer affect the performance of the overall membrane stack. In this paper, we present a simplified mathematical model to describe how the pore-scale properties of a multilayered membrane affect the overall filter performance. Our results show that, for membrane stacks where the initial layer porosity decreases with depth, larger (negative) porosity gradients within a filter membrane are favorable for increasing throughput and filter lifetime, but at the expense of moderately poorer initial particle retention. We also found that the optimal layer thickness distribution that maximizes total throughput corresponds to a membrane stack with larger (negative) porosity gradients in which layer thickness increases slightly between successive layers in the depth of the membrane.

A robust dually charged membrane prepared via catechol-amine chemistry for highly efficient dye/salt separation

Novel nanoporous membranes with superior permeability and exceptional molecular selectivity are highly desirable for wastewater treatment and reclamation. Herein, a 3D dual-charged multilayer membrane for efficient separation of dyes/salts is fabricated via catechol-amine chemistry surface engineering. Polyethyleneimine (PEI) is firstly coated on the hydrolyzed polyacrylonitrile substrate to construct a positively charged intermediate layer, followed by codeposition of tannic acid (TA) and poly-γ-glutamic acid (γ-PGA) to engineer a negatively charged top layer. During the polyphenol-induced competitive reaction processes, covalent interactions, hydrogen bonding and electrostatic adsorption among TA, γ-PGA and PEI hinder the rapid and uneven self-polymerization of TA, thus loosening the separation layer structure. In addition, the pre-reaction between TA and γ-PGA can weaken those competitive reactions, further tuning the pore size and dual charge layer thus improving the separation performance. Benefited from the novel loose dual-charged structure, the resultant membrane exhibits outstanding water permeability (36.9 Lm−2h−1bar−1) with low salt rejections (11.1% for Na2SO4 and 14.6% for NaCl) and high rejection to both positively and negatively charged dyes. It works well even for rejecting small-molecule dyes (100% congo red, 98% methyl green, 96% methyl orange and 86% methylene blue), far superior to the state-of-the-art membranes. Despite the loose structure, the membrane still possesses excellent acid resistance, and its hydrophilic surface contributes to excellent anti-fouling performance. Such thin-film composite membranes with tunable dual-charged multilayer prepared via this new strategy provides a promising candidate for separation of small charged molecules and inorganic salts, especially in textile industry.

Unidirectional Water-Transport Antibacterial Trilayered Nanofiber-Based Wound Dressings Induced by Hydrophilic-Hydrophobic Gradient and Self-Pumping Effects

Excessive wound exudates often cause infection and hinder wound repair and regeneration. It is therefore urgently needed to develop an ideal wound dressing for pumping the excessive biofluids and inhibiting bacterial infection in the wound healing process. Herein, we demonstrate a facile and efficient strategy to fabricate the unidirectional water-transport antibacterial wound dressings by embedding macromolecular antimicrobials into a multilayer nanofibrous membrane featured with hydrophobic-to-hydrophilic gradient structure and self-pumping effect using an electrospinning technique. Thanks to these features, the obtained nanofibrous dressings achieved excellent unidirectional water-transport performance, which could drive wound exudates to flow spontaneously from inside to outside and prevent pumped biofluids rewetting the wounds. In addition, the designed trilayered dressing exhibited approximately 100% antibacterial ability against Staphylococcus aureus and Escherichia coli when the concentration of antibacterial agents polyhexamethylene guanidine hydrochloride (PHGC) was 0.06 wt%. Moreover, the trilayered dressings revealed excellent water absorption performance, air and moisture permeability, mechanical strength, biocompatibility, and low cell adhesion behavior, indicating the potential applications for the trilayered nanofibrous wound dressings in wound care.

Fractionation of Tilapia By-Product Protein Hydrolysate Using Multilayer Configuration of Ultrafiltration Membrane

Production of small-sized peptides is significant because of their health benefits. Ultrafiltration (UF) membrane provides an effective fractionation of small-sized peptides on a large scale. Thus, the present study was aimed to evaluate the performance of multilayer UF membrane in fractionating tilapia fish by-product (TB) protein hydrolysate by observing the permeate flux, peptide transmission, and peptide distribution under different stirring speed, pH of feed solution, and salt concentration (NaCl). The fractionation process was carried out using a dead-end UF membrane system that consists of a stack of two membrane sheets with different (10/5 kDa) and similar (5/5 kDa) pore sizes in one device. The highest permeate flux (10/5 kDa–39.5 to 47.3 L/m2.h; 5/5 kDa– 15.8 to 20.3 L/m2.h) and peptide transmission (10/5 kDa–51.8 to 61.0%; 5/5 kDa–18.3 to 23.3%) for both multilayer membrane configurations were obtained at 3.0 bar, 600 rpm, pH 8, and without the addition of salt. It was also found that the permeates were enriched with small-size peptides (<500 Da) with a concentration of 0.58 g/L (10/5 kDa) and 0.65 g/L (5/5 kDa) as compared to large-sized peptides (500–1500 Da) with concentration of 0.56 g/L (10/5 kDa) and 0.36 g/L (5/5 kDa). This might indicate the enrichment of small-size peptides through the multilayer membrane which could potentially enhance the biological activity of the protein hydrolysate fraction.

Effect of the orientation of sulfonated graphene oxide (SG) on the gas-barrier properties and proton conductivity of a SG/Nafion composite membrane

In a proton-exchange membrane fuel cell, the proton-exchange membrane is located between the oxidant and the fuel, which facilitates proton conduction and prevents the penetration of gas molecules. In this study, sulfonated graphene oxides (SG) were synthesized, and a series of SG/Nafion composite multilayer membranes were prepared using layer-by-layer assembling. This multilayer membrane-structure has an efficient orientation effect on the SG sheets. The thinner the layer is, the more significant is the orientation effect. A statistical angle between the SG sheets and the membrane surface (Θ) is used to represent the orientation of SG sheets, and a correlation between the thickness of the layers and Θ is found. Under various conditions, these multilayer composite membranes improve the gas-barrier properties (H2, O2, and water vapor) and proton conductivity. The effect of Θ on the gas-barrier properties and proton conductivity of the membranes is discussed. Our results reveal that the SG sheets have excellent gas-barrier properties in the longitudinal direction and good proton conductivity in the lateral direction. Furthermore, based on positron-annihilation lifetime spectroscopy, it is found that the diffusion coefficients of gas molecules in all the SG/Nafion composite membranes are almost identical. In other words, the orientation of the SG sheets changes the gas-barrier properties of the membranes by altering the morphology of the diffusion paths for the gas molecules during the permeation.

Enhancing the Ultraviolet Photocurrent and Response Speed of Zinc Oxide Nanoflowers using Surface Plasmons of Gold Nanoparticles and a Graphene Membrane

The enhancement effect of the plasmonic resonance of AuNPs and a graphene membrane on the optoelectronic properties of ZnO nanoflowers is investigated. A layered structure is fabricated, consisting of ZnO nanoflowers grown on a conductive fluorine‐doped tin oxide (FTO) glass substrate, decorated with gold nanoparticles, and covered by a multilayer graphene membrane. An excellent photocurrent response as high as 1650 A W−1 and a millisecond level response time are achieved. Compared with the pristine ZnO device, which has a responsivity of 2.98 A W−1 and a response time of tens of seconds, the photocurrent response is dramatically increased by 500‐fold and the response time is decreased by over 1000‐fold. The significant enhancement of the photocurrent can be attributed to the coupling of plasmonic resonance modes of AuNPs and the graphene membrane, according to finite‐difference time‐domain simulation results; whereas the tremendous improvement on response time can be attributed to the high electron mobility of graphene. The work is essential for further study of the plasmonic enhancement of ZnO optoelectronic performance and provides a new path for the fabrication of ZnO‐based high‐responsivity, high‐speed, and low‐cost ultraviolet emission and detection devices.

On the desalination performance of multi-layer graphene membranes; A molecular dynamics study

In this study, the efficiency of a multi-layer graphene membrane with fully aligned pores was discussed in the desalination process. By changing the configurations and parameters such as pore size, pressure, thickness, ion concentration, and pore geometry, the water transfer rate has been observed from the scale 100 to 1000 L/m2 h bar, which is very close to the transfer rate of water through single-layer graphene sheet and three times larger than conventional reverse osmosis membranes. Small pores (with 0.6 nm in diameter) in the multi-layered graphene membrane pass a small water flow rate even when the high pressures. More water flow rate could be achieved in larger pores, but in the pores with diameters larger than 1.2 nm, the salt rejection is weakened. Increasing the number of layers from five to ten can completely cease the water flow in the same pore diameter. With a 40% reduction in the concentration of ions in the feed area, the water transfer rate is increased by about half. The results of this study can be useful for making a superior membrane for future water crises.

Efficient Facilitated Transport Polymer Membrane for CO2/CH4 Separation from Oilfield Associated Gas.

CO2 enhanced oil recovery (CO2-EOR) technology is a competitive strategy to improve oil field economic returns and reduce greenhouse gas emissions. However, the arbitrary emissions or combustion of the associated gas, which mainly consists of CO2 and CH4, will cause the aggravation of the greenhouse effect and a huge waste of resources. In this paper, the high-performance facilitated transport multilayer composite membrane for CO2/CH4 separation was prepared by individually adjusting the membrane structure of each layer. The effect of test conditions on the CO2/CH4 separation performance was systematically investigated. The membrane exhibits high CO2 permeance of 3.451 × 10−7 mol·m−2·s−1·Pa−1 and CO2/CH4 selectivity of 62 at 298 K and 0.15 MPa feed gas pressure. The cost analysis was investigated by simulating the two-stage system. When the recovery rate and purity of CH4 are 98%, the minimum specific cost of separating CO2/CH4 (45/55 vol%) can be reduced to 0.046 $·Nm−3 CH4. The excellent short-to-mid-term stability indicates the great potential of large industrial application in the CH4 recovery and CO2 reinjection from oilfield associated gas.