Multilayer Membranes Research Articles

Asymmetric multilayered cellulose nanofiber composite membranes with electrical-magnetic dual-gradient architectures towards excellent electromagnetic interference shielding performance

The structural design strategies of MXene-based nanocomposites have demonstrated critical significance for electromagnetic interference (EMI) shielding applications. Herein, novel asymmetric multilayered cellulose nanofiber/multiwalled carbon nanotube@ferroferric oxide/MXene (CNF/MWCNT@Fe3O4/MXene) composite membranes with electrical-magnetic dual-gradient structures were prepared via layered-by-layered self-assembly strategy. Briefly, CNF/MWCNT@Fe3O4 layers are designed as the negative gradient absorption layers which provide dielectric/magnetic double loss. Meanwhile, MXene layers serve as the positive gradient reflection layers which generate multiple reflections and conduct loss. Thus, gradient multilayered CNF/MWCNT@Fe3O4/MXene composite membranes exhibit a total electromagnetic interference shielding effectiveness (EMI SET) of 73.20 dB at the thickness of 180 μm and R-value of 0.99934 in the X-band. Furthermore, the asymmetric gradient multilayer composite membrane reveals a superior EMI shielding performance in comparison with that of homogeneous multilayered composite membranes. When electromagnetic waves (EMWs) pass through the gradient multilayered CNF/MWCNT@Fe3O4/MXene composite membrane, the rational asymmetric gradient multilayered structures contribute to a “gradually decreasing absorption-gradually increasing reflection” shielding mechanism. Thereby, the design strategy of asymmetric electrical-magnetic dual-gradient structures is advantageous in enhancing the EMI shielding ability of polymeric composites.

Electroactive polylactic acid nanofiber multilayer membranes as “Green” flexible electrode for supercapacitor

Against the backdrop of the post-COVID-19 era, the demand for masks has become increasingly steady, discarded masks have brought about new environmental problems due to the lack of effective means of disposal as well as recycling mechanisms. To solve this problem, we make secondary use of discarded polylactic acid (PLA) masks. The nanofiber multilayer membranes PLA/PDA/GO/PPy were synthesized by layer-by-layer self-assembly for flexible supercapacitors (SCs). The multiple coating on PLA significantly increases the capacitive performance. Optimization of the PLA/PDA/GO/PPy demonstrates capacitance up to 1331 mF cm−2. Symmetric aqueous SCs using PLA/PDA/GO/PPy electrodes show higher energy density than other literature-reported SCs based on nanofiber multilayer membranes. In addition, we also explored the effects of discarded PLA/PDA/GO/PPy on the growth of ryegrass and canola in the soil. The exceptional combination of remarkable electrochemical properties and excellent environmental friendliness makes the PLA membrane promising for supercapacitors.

Bilateral Aggressive Mooren Ulcer in the Setting of Bilateral Pterygia and Pregnancy: A Unique Case.

To report an unusual case of bilateral aggressive Mooren ulcer that occurred in the setting of bilateral pterygia and showed a relentless course during pregnancy. A 39-year-old woman of Black African ethnicity, 36-week pregnant, presented to the eye casualty with bilateral nasal corneal ulcer and associated melt around preexisting pterygia. A detailed workup including microbial evaluation, culture and sensitivity, polymerase chain reaction for herpes simplex virus, varicella zoster virus, and cytomegalovirus, inflammatory blood profile, autoimmune markers, and human leucocyte antigen (HLA) screening was undertaken. Treatment was initiated in a stepwise approach. Infections and systemic autoimmune and rheumatologic conditions were ruled out. A diagnosis of bilateral Mooren ulcer was made by exclusion. The peripheral blood was positive for HLA DQ2. As the condition seemed refractory to medical management (topical steroids and intravenous pulse methylprednisolone followed by oral prednisolone and topical cyclosporine), urgent bilateral conjunctival resection with multilayered amniotic membrane transplantation was performed to reduce the inflammatory stimulus and keratolysis. Stabilization of the condition warranted the need for systemic immunosuppressive agents. Using a multidisciplinary approach, in liaison with Obstetricians and Rheumatologists, the patient was planned for an earlier elective Cesarean section and commencement of oral mycophenolate mofetil postpartum, which aided in successful control of the disease. Mooren ulcer could follow an aggressive course during pregnancy, especially in the setting of preexisting pterygium. The complex hormonal and immunological changes during pregnancy and the delivery of inflammatory mediators directly onto the cornea by pterygium could contribute to the severity. A well-planned, stepwise, and multidisciplinary management is pivotal for the treatment of this condition.

On‐Chip THz Helical Antenna Based on Metal Self‐Rolled‐up Membrane Nanotechnology

AbstractThis paper demonstrates the on‐chip terahertz (THz) helical antenna based on metal self‐rolled‐up membrane (M‐SRuM) nanotechnology, which utilizes the residual stress in multilayer metal membrane deposited by electron beam (E‐beam) evaporation to provide the rolling force and to form the radiation body of the helical antenna. Precise design method is proposed based on multi‐physics modeling for mechanical and electrical analysis, and the two operating modes of on‐chip helical antenna are modeled and analyzed. The test results show that the normal mode of self‐rolled‐up THz helical antenna is able to operate at frequency as high as 0.223 THz with the corresponding impedance bandwidth of 13 GHz.

Acidochromic Free-Standing Multilayered Chitosan-Pyranoflavylium/Alginate Membranes toward Food Smart Packaging Applications.

Food smart packaging has emerged as a promising technology to address consumer concerns regarding food conservation and food safety. In this context, we report the rational design of azide-containing pyranoflavylium-based pH-sensitive dye for subsequent click chemistry conjugation toward a chitosan-modified alkyne. The chitosan-pyranoflavylium conjugate was characterized by infrared (ATR-FTIR), ultraviolet-visible (UV-vis), nuclear magnetic resonance (NMR) spectroscopies, and dynamic light scattering (DLS), as well as its thermodynamic parameters related to their pH-dependent chromatic features. The fabrication of thin-films through electrostatic-driven layer-by-layer (LbL) assembly technology was first screened by quartz crystal microbalance with dissipation monitoring (QCM-D) onto gold substrates, and then free-standing (FS) multilayered membranes from polypropylene substrate were obtained using a homemade automatic dipping robot. The membranes' characterization included morphology analysis and thickness evaluation, assessed by scanning electron microscopy (SEM), pH-responsive color change performance tests using buffer solutions at different pH levels, and biogenic amines-enriched model solutions, demonstrating the feasibility and effectiveness of the chitosan-pyranoflavylium/alginate biomembranes for food spoilage monitoring. This work provides insights toward the development of innovative pH-responsive smart biomaterials for advanced and sustainable technological packaging solutions, which could significantly contribute to ensuring food safety and quality, while reducing food waste.

Eco-Friendly Superhydrophobic Modification of Low-Cost Multi-Layer Composite Mullite Base Tubular Ceramic Membrane for Water Desalination

This study aimed to investigate and develop a cost-effective and superhydrophobic ceramic membrane for direct contact membrane distillation (DCMD) applications. Two types of mullite-based composite membranes were prepared via extrusion and sintering techniques. To create a small and narrow pore diameter distribution on the membrane surface, the dip-coating technique with 1 µm alumina was employed. The hexadecyltrimethoxysilane eco-friendly grafting agent was adopted to modify low-cost multilayer mullite-based composite membranes, transforming them from hydrophilic to superhydrophobic. The prepared membranes were characterized via field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), liquid entire pressure (LEP), contact angle, atomic force microscopy (AFM), porosity, and membrane permeability. The results of the prepared membranes validate the appropriateness of the material for membrane distillation applications. The optimized membrane, with a contact angle of 160° and LEP = 1.5 bar, was tested under DCMD using a 3.5 wt.% sodium chloride (NaCl) synthetic solution and Persian Gulf seawater as a feed. Based on the acquired results, an average permeate flux of 3.15 kg/(m2·h) and salt rejection (R%) of 99.62% were found for the 3.5 wt.% NaCl solution. Moreover, seawater desalination showed an average permeate flux of 2.37 kg/(m2·h) and salt rejection of 99.81% for a 20-h test without any pore wetting. Membrane distillation with a hydrophobic membrane decreased the turbidity of seawater by 93.13%.

Comparative Retention Analysis of Intercalated Cations Inside the Interlayer Gallery of Lamellar and Nonlamellar Graphene Oxide Membranes in Reverse Osmosis Process: A Molecular Dynamics Study.

Over the past decade, multilayered graphene oxide (GO) membranes have emerged as promising candidates for desalination applications. Despite their potential, a comprehensive understanding of separation mechanisms remains elusive due to the intricate morphology and structural arrangement of interlayer galleries. Moreover, a critical concern of multilayered GO membranes is their susceptibility to swelling within aqueous environments, which hinders their practical implementation. Therefore, this study introduces cation intercalation within GO laminates to elucidate the underlying factors governing swelling behavior and subsequently mitigate it. Moreover, this study performed nonequilibrium molecular dynamics simulations on the cation (Mg2+ or K+)-intercalated lamellar and nonlamellar GO membranes to understand the effect of the arrangement of GO sheets on the retention time of intercalated cations within GO layers, water permeance, and salt rejection mechanism in the reverse osmosis process using cation-intercalated GO membranes. Our results highlight that lamellar GO membranes exhibit higher water permeance, attributed to their well-defined interlayer gallery structure. On the other hand, nonlamellar GO membranes display superior salt rejection due to their complex interlayer gallery structure that impedes salt permeation. Moreover, the structural complexity of nonlamellar GO membranes contributes to greater stability by retention of the more intercalated cations for a longer time within the layers. Furthermore, it is observed that a higher percentage of Mg2+ cations remained inside the GO laminates as compared to K+ cations, hence resulting in the greater stability of the Mg2+-intercalated GO membrane in the aqueous environment.

Optimal permeance ratio, flux direction and layer distribution in composite asymmetric membranes composed of sequences of layers obeying real-power flux laws

In this study, the optimal permeance ratio and layers distribution in multilayer membranes and thin films in which each layer obeys the following real-power law: Flux=πi(P1,ini−P2,ini) are determined for any positive real values of ni. Such an exponent has a physical meaning in several cases, such as: diffusion-controlled permeation of hydrogen in metal membranes i) under infinite-dilution conditions (n = 0.5), and ii) under higher-concentration ones (0.5 < n < 1.5), iii) desorption-limited permeation (n = 1) in the same type of membranes, Knudsen-type diffusional mechanism (n = 1) and viscous flow (n = 2) in microporous membranes. Furthermore, n is equal to 4 in radiation-driven thermal flux. The work considers two generic layers of different thicknesses and exponents, for which it is proven the existence of a general optimal permeance ratio π1/π2 maximising the flux ratio, which is found to be equal to the inverse of the ratio between the respective maximum theoretical driving forces that can be established in each layer. Such an optimal permeance ratio is also proven to be a global optimum. Afterwards, we provide a theoretical generalisation of this optimality to whatever types of driving forces. Then, we provide a demonstration that the highest species permeating flux is always established when feeding it from the layer side with the highest exponent independently of the permeance ratio. As an important consequence, to maximise flux, a multilayer membrane/thin film should be fabricated by depositing the layers in cascade according to the ascending or descending exponents, and should be used in a configuration in which the flux flows from the layer with the highest pressure exponent to the layer with the lowest one. It is also shown that there exists an optimal value of the lower exponent n1 that maximizes the flux ratio keeping constant the other parameters. Finally, we showed that a virial-type linear combination of polynomial driving forces can be approximated by the empirical flux law investigated. Overall, our results are valid not only for whatever type of composite membranes and thin films (metallic, ceramic, polymeric and hybrid ones), but also for any sequential system involving a flux of whatever physical entity obeying the aforementioned law, such as heat transfer in the presence of radiation, non-linear electrical resistances and possible others.

All-Printed Finger-Inspired Tactile Sensor Array for Microscale Texture Detection and 3D Reconstruction.

Electronic skins are expected to replicate a human-like tactile sense, which significantly detects surface information, including geometry, material, and temperature. Although most texture features can be sensed in the horizontal direction, the lack of effective approaches for detecting vertical properties limits the development of artificial skin based on tactile sensors. In this study, an all-printed finger-inspired tactile sensor array is developed to realize the 3D detection and reconstruction of microscale structures. A beam structure with a suspended multilayer membrane is proposed, and a tactile sensor array of 12 units arranged in a dual-column layout is developed. This architecture enables the tactile sensor array to obtain comprehensive geometric information of micro-textures, including 3D morphology and clearance characteristics, and optimizes the 3D reconstruction patterns by self-calibration. Moreover, an innovative screen-printing technology incorporating multilayer printing and sacrificial-layer techniques is adopted to print the entire device. In additon, a Braille recognition system utilizing this tactile sensor array is developed to interpret Shakespeare's quotes printed in Grade 2 Braille. The abovementioned demonstrations reveal an attractive future vision for endowing bioinspired robots with the unique capability of touching and feeling the microscale real world and reconstructing it in the cyber world.

Efficient Cr(VI) remediation by electrospun composite porous nanofibers incorporating biomass with metal oxides and metal-organic framework

To develop a highly efficient adsorbent to remediate and remove hexavalent chromium ions (Cr(VI)) from polluted water, cellulose acetate (CA) and chitosan (CS), along with metal oxides (titanium dioxide (TiO2) and ferroferric oxide (Fe3O4)), and a zirconium-based metal-organic framework (UiO-66) were used to fabricate the composite porous nanofiber membranes through electrospinning. The adsorption performance, influencing factors, adsorption kinetics and isotherms of composite nanofiber membranes were comprehensively investigated. The multi-layer membrane with interpenetrating nanofibers and surface functional groups enhanced the natural physical adsorption and provided potential chemical sites. The thermal stability was improved by introducing TiO2 and UiO-66. CA/CS/UiO-66 exhibited the highest adsorption capacity (118.81 mg g−1) and removal rate (60.76%), which were twice higher than those of the control. The correlation coefficients (R2) of all the composite nanofibers regressed by the Langmuir model were significantly higher than those by the Freundlich model. The pseudo-first-order kinetic curve of CA/CS composite nanofibers showed the highest R2 (0.973), demonstrating that the whole adsorption process involved a combination of strong physical adsorption and weak chemical adsorption by the amino groups of CS. However, the R2 values of the pseudo-second-order kinetic model increased after incorporating TiO2, Fe3O4, and UiO-66 into the CA/CS composite nanofiber membranes since an enhanced chemical reaction with Cr (VI) occured during the adsorption

Programmable photoacoustic patterning of microparticles in air.

Optical and acoustic tweezers, despite operating on different physical principles, offer non-contact manipulation of microscopic and mesoscopic objects, making them essential in fields like cell biology, medicine, and nanotechnology. The advantages and limitations of optical and acoustic manipulation complement each other, particularly in terms of trapping size, force intensity, and flexibility. We use photoacoustic effects to generate localized Lamb wave fields capable of mapping arbitrary laser pattern shapes. By using localized Lamb waves to vibrate the surface of the multilayer membrane, we can pattern tens of thousands of microscopic particles into the desired pattern simultaneously. Moreover, by quickly and successively adjusting the laser shape, microparticles flow dynamically along the corresponding elastic wave fields, creating a frame-by-frame animation. Our approach merges the programmable adaptability of optical tweezers with the potent manipulation capabilities of acoustic waves, paving the way for wave-based manipulation techniques, such as microparticle assembly, biological synthesis, and microsystems.

Structural color tunable intelligent mid-infrared thermal control emitter

This work proposes a colored intelligent thermal control emitter characterized by adjustable structural color development with a reflection spectrum in the visible light range and intelligent thermal control with temperature switching in the mid infrared wavelength band. In the beginning, we investigate an intelligent thermal control emitter based on a multilayer membrane formed by the phase change material vanadium dioxide, metal material Ag, and dielectric materials Ge and ZnS. By incorporating the thermochromic material vanadium dioxide, the structure exhibits a high emissivity of εH = 0.85 in the range of 3–13 μm wavelength when in the high temperature metallic state, enabling efficient heat radiation. In the low temperature dielectric state, the structure only has a low emission capacity of εL = 0.07, reducing energy loss. Our results demonstrate that the structure achieves excellent emission regulation ability (Δε = 0.78) through the thermal radiation modulation from high to low temperature, maintaining effective thermal control. Furthermore, the thermal control emitter exhibits selective emission of peak wavelength due to destructive interference and shows a certain independence on polarization and incidence angle. Additionally, the integration of structural color adjustment capability enhances the visual aesthetics of the human experience. The proposed colored intelligent thermal control structure has significant potential for development in aesthetic items such as colored architecture and energy-efficient materials.

The study of multilayer graphene membrane performance in O2 purification process: Molecular dynamics simulation

We use molecular dynamics (MD) method to describe the atomic behavior of Graphene nanostructure for Oxygen molecules (O2) separation from Carbon dioxide (CO2) molecules. Technically, for the simulation of graphene-based membrane and O2-CO2 gas mixture, we used Tersoff and DREIDING force fields, respectively. The result of equilibrium process of these structures indicated the good stability of them. Physically, this behavior arises from the appropriate MD simulation settings. Furthermore, to describe the purification performance of graphene-based membrane, we report some physical parameters such as purification value, impurity rate, and permeability of membrane after atomic filtering process. Numerically, by defined membranes optimization, the purification value of them reach to 97.31%. Also, by using these atomic structures the CO2 impurity which passed from graphene-based membrane reach to zero value.

Traumatic terson syndrome with a peculiar mass lesion and tractional retinal detachment: a case report

BackgroundTo report a case with bilateral Terson syndrome presented with a unique mushroom-like mass lesion on the optic disc along with proliferative vitreoretinopathy and tractional retinal detachment.Case presentationA 33-year-old man was injured during a traffic accident and had diffuse brain swelling and intraocular hemorrhage. Poor vision in both eyes was noted after the patient regained consciousness. B-scan ultrasonography showed extensive vitreous opacity with a posterior vitreous detachment and without obvious retinal detachment. Vitrectomy was performed in both eyes five months after the accident. After clearing up the vitreous opacity, a peculiar pigmented mushroom-like mass lesion was noted in the posterior pole and had severe adhesion to the underneath optic disc. Extensive multilayered peripapillary epiretinal membrane was found covering the posterior pole and led to tractional retinal detachment around the macula. The mass was presumed to be an organized vitreous hemorrhage originated from the optic disc. The extensive and adherent epiretinal membrane together with the mass lesion were removed as much as possible and silicon oil was injected for tamponade. However, in the right eye, the retina redetached under silicon oil, whereas in the left eye, his vision improved to 20/100.ConclusionsTerson syndrome usually has a favorable prognosis but may be complicated by proliferative vitreoretinopathy and tractional retinal detachment. Careful monitoring is warranted and early vitrectomy should be considered in cases suspecting additional pathologies.

Progress on 3D tubular passive electronics: Residual stress-based fabrication, application, and modeling

The platform concept and methodology to create three-dimensional (3D) tubular structures by releasing the stress of two-dimensional multilayer membranes has been demonstrated for the design and fabrication of advanced integrated passive electronics, which revolutionizes their design and fabrication, enabling extraordinarily strong electromagnetic coupling effects and high energy storage densities, for the miniaturization of a variety of systems. In this perspective, we highlight the important recent progress, which constitutes the scope of understanding of 3D tubular passive electronics, including fabrication techniques, applications, and multi-physics modeling. Basic 3D tubular inductive and capacitive components are discussed, in addition to complex and composite devices and systems such as transformers, filters, and antennas. Finally, state-of-the-art strategies to engineer reconfigurable 3D tubular structures are discussed, with the intention to inspire a more disruptive design of passive electronics.

Flexible Piezoresistive Sensors Based on PPy Granule-Anchored Multilayer Fibrous Membranes with a Wide Operating Range and High Sensitivity.

The employment of flexible piezoresistive sensors has sparked growing interest within the realm of wearable electronic devices, specifically in the fields of health detection and e-skin. Nevertheless, the advancement of piezoresistive sensors has been impeded by their limited sensitivity and restricted operating ranges. Consequently, it is imperative to fabricate sensors with heightened sensitivity and expanded operating ranges through the utilization of the appropriate methodologies. In this paper, piezoresistive sensors were fabricated utilizing electrospun polyvinylidene fluoride/polyacrylonitrile/polyethylene-polypropylene glycol multilayer fibrous membranes anchored with polypyrrole granules as the sensing layer, while electrospun thermoplastic polyurethane (TPU) fibers were employed as the flexible substrate. The sensitivity of the sensor is investigated by varying the fiber diameter of the sensing layer. The experimental findings reveal that a concentration of 14 wt % in the spinning solution exhibits high sensitivity (996.7 kPa-1) within a wide working range (0-10 kPa). This is attributed to the favorable diameter of the fibers prepared at this concentration, which facilitates the uniform in situ growth of pyrrole. The highly deformable TPU flexible fibers and multilayer sensing layer structure enable different linear responses across a broad pressure range (0-1 MPa). Furthermore, the sensor demonstrates good cyclic stability and can detect human movements under different pressures. These results suggest that the piezoresistive sensor with a wide operating range and high sensitivity has significant potential for future health monitoring and artificial intelligence applications.

Preparation of stable multilayer PDMS composite pervaporation membrane incorporated with in-situ transformed metal organic frameworks for enhanced butanol recovery

In this study, stable and non-defective multilayer polydimethylsiloxane (PDMS) composite pervaporation mixed matrix membranes incorporated with in-situ transformed metal organic frameworks was successfully synthesized via ligand vapor phase infiltration and spin-coating. Metal zinc sources were uniformly distributed in PDMS which were in-situ transformed into homogeneous zeolitic imidazolate framework-8 (ZIF-8) nanoparticles, effectively alleviating the aggregation of ZIF-8. Thermal cross-linking of PDMS and the formation of MOFs occurred simultaneously, omitting the complicated preparation and re-dispersion steps of MOF nanoparticles. MOF nanoparticles and PDMS formed a more stabilized composite structure by in-situ transformation, in which PDMS and metal of MOFs can interact with the -Si-O- of silane coupling groups on membrane surface to construct solid multilayer composite membrane, ensuring long-term stability. Moreover, with the aid of hydrophobic interlayer, polymer infiltration into channels of substrate was restricted and casting solution spread out smoothly, facilitating the formation of defect-free PDMS selective layer. Various techniques including Attenuated Total Reflection-Fourier Transform Infrared Spectrometer, Field Emission Scanning Electron Microscopy, Atomic Force Microscope and X-ray Diffraction were applied to explore the morphology, composition and structure of nanoparticles and membranes, and pervaporation tests were taken to investigate the behavior of hydrophobic polymer-based multilayer membranes. For the recovery of low concentration n-butanol, the prepared non-defective multilayer TAO/ZIF-8/K-PDMS composite membrane displayed excellently total permeate flux of 2890 g m−2 h−1 with competitive separation factor of 40.3.

Multilayer hybrid solid-state electrolyte membrane for the high rate and long-life cycle performance of lithium-metal batteries

Hybrid solid-state electrolytes (HSEs) can be used to increase the electrochemical performance of lithium-metal batteries (LMBs), while also suppressing dendrite formation and preventing flammable behavior and electrolyte leakage, which are frequently present in conventional organic-liquid electrolytes. Notably, multilayer HSE membranes have received increasing emphasis since they can significantly ameliorate the interface contact toward electrodes and the mechanical strength. In this current work, we fabricated multilayer HSE membranes via a solution-casting technique that incorporated poly(vinylidene fluoride–co–hexafluoropropylene) (PVDF-HFP), polydopamine-modified Li6.28La3Zr2Al0.24O12 (PDA@LLZAO) filler, succinonitrile (SN) and lithium bis(trifluoromethane sulfonyl)imide (LiTFSI). The resulting HSE membrane exhibited a high ionic conductivity (2.49 ×10−4 S cm−1 at 30 ℃), transference number of 0.65, and excellent electrochemical window (4.80 V). The symmetrical cell featuring Li/HSE/Li was stable and cycled without short circuiting for 1000 h during the Li plating/stripping cycles. Furthermore, the coin-type cell assembled with LiFePO4/HSE/Li showed an initial discharge capacity of 134.7 mAh g1 and exhibited superior retained capacity and average coulombic efficiency of 93.45% and 99.39%, respectively, after 687 cycles at 2 C and 30 ℃. Therefore, the as-prepared multilayer HSE is a promising SSE for next-generation LMBs.

Theoretical and experimental research of polyelectrolyte multilayer membrane prepared by layer by layer self-assembly

Layer-by-layer self-assembly of polyelectrolytes is one of the most promising methods for preparing nanofiltration membranes. Here poly (sodium 4-styrenesulfonate) (PSS) and poly (diallyldim-ethylammonium chloride) (PDADMAC) were chosen to prepare polyelectrolyte multilayer (PEM) membrane. The effects of background salt concentration, PSS concentration, background salt types, the number of layers and the outermost functional groups on the separation performance of the PEM were investigated systematically. Molecular dynamic simulation was employed to simulate the influence of background salt on the diffusion of PDADMAC. The simulation results agree well with the experimental results. The optimized (PSS/PDADMAC)4.5 membrane with Na2SO4 as background salt shows permeance of 15.9 LMH/bar, Na2SO4 rejection of 98.2 %, and an excellent stability. Our study provides both theoretical and experimental supports for the preparation of PEM membranes using LBL method.

Effect of air-loading on the performance limits of graphene microphones

As a consequence of their high strength, small thickness, and high flexibility, ultrathin graphene membranes show great potential for pressure and sound sensing applications. This study investigates the performance of multi-layer graphene membranes for microphone applications in the presence of air-loading. Since microphones need a flatband response over the full audible bandwidth, they require a sufficiently high mechanical resonance frequency. Reducing membrane thickness facilitates meeting this bandwidth requirement, and therefore, also allows increasing compliance and sensitivity of the membranes. However, at atmospheric pressure, air-loading effects can increase the effective mass, and thus, reduce the bandwidth of graphene and other 2D material-based microphones. To assess the severity of this performance-limiting effect, we characterize the acoustic response of multi-layer graphene membranes with a thickness of 8 nm in the pressure range from 30 to 1000 mbar, in air and helium environments. A bandwidth reduction by a factor ∼2.8× for membranes with a diameter of 500 μm is observed. These measurements show that air-loading effects, which are usually negligible in conventional microphones, can lead to a substantial bandwidth reduction in ultrathin graphene microphones. With analytical and finite element models, we further analyze the performance limits of graphene microphones in the presence of air-loading effects.