Ultrathin Membranes Research Articles

A computer vision approach for analyzing label free leukocyte trafficking dynamics on a microvascular mimetic.

High-content imaging techniques in conjunction with in vitro microphysiological systems (MPS) allow for novel explorations of physiological phenomena with a high degree of translational relevance due to the usage of human cell lines. MPS featuring ultrathin and nanoporous silicon nitride membranes (µSiM) have been utilized in the past to facilitate high magnification phase contrast microscopy recordings of leukocyte trafficking events in a living mimetic of the human vascular microenvironment. Notably, the imaging plane can be set directly at the endothelial interface in a µSiM device, resulting in a high-resolution capture of an endothelial cell (EC) and leukocyte coculture reacting to different stimulatory conditions. The abundance of data generated from recording observations at this interface can be used to elucidate disease mechanisms related to vascular barrier dysfunction, such as sepsis. The appearance of leukocytes in these recordings is dynamic, changing in character, location and time. Consequently, conventional image processing techniques are incapable of extracting the spatiotemporal profiles and bulk statistics of numerous leukocytes responding to a disease state, necessitating labor-intensive manual processing, a significant limitation of this approach. Here we describe a machine learning pipeline that uses a semantic segmentation algorithm and classification script that, in combination, is capable of automated and label-free leukocyte trafficking analysis in a coculture mimetic. The developed computational toolset has demonstrable parity with manually tabulated datasets when characterizing leukocyte spatiotemporal behavior, is computationally efficient and capable of managing large imaging datasets in a semi-automated manner.

Progress and Prospects of Inorganic Solid-State Electrolyte-Based All-Solid-State Pouch Cells.

All-solid-state batteries have piqued global research interest because of their unprecedented safety and high energy density. Significant advances have been made in achieving high room-temperature ionic conductivity and good air stability of solid-state electrolytes (SSEs), mitigating the challenges at the electrode-electrolyte interface, and developing feasible manufacturing processes. Along with the advances in fundamental study, all-solid-state pouch cells using inorganic SSEs have been widely demonstrated, revealing their immense potential for industrialization. This review provides an overview of inorganic all-solid-state pouch cells, focusing on ultrathin SSE membranes, sheet-type thick solid-state electrodes, and bipolar stacking. Moreover, several critical parameters directly influencing the energy density of all-solid-state Li-ion and lithium-sulfur pouch cells are outlined. Finally, perspectives on all-solid-state pouch cells are provided and specific metrics to meet certain energy density targets are specified. This review looks to facilitate the development of inorganic all-solid-state pouch cells with high energy density and excellent safety.

Large-Area Fabrication of Ultrathin Metal-Organic Framework Membranes.

Metal-organic framework (MOF)-based membranes, featuring potential molecular sieving effects and therefore capable of surmounting the ubiquitous trade-off between membrane selectivity and permeability, hold great promise for multitudinous chemical separations. Nevertheless, it remains highly challenging for the large-area fabrication of ultrathin MOF membranes with variable thickness, great homogeneity, and preferential orientation. Herein, this work reports the facile fabrication of ultrathin (down to 20nm) NUS-8 membranes in large-area (>200 cm2 ) yet with great homogeneity and texture along (00l) direction due to the superior solution processability of the as-synthesized NUS-8 nanosheets. The resultant NUS-8 membranes with good adhesion properties and certain flexibility exhibit excellent rejections (>98% for Mg2+ and Al3+ , and dyes with molecular weights larger than 585.5 g mol-1 ) toward aqueous separation of various metal ions and dyes at modest permeance (1-3.2 L m-2 h-1 bar-1 ) due to the well-aligned structures. Such separation performance outstands among polymetric membranes, thin-film composite membranes, mixed matrix membranes, and other MOF membranes reported in the literature. The separation mechanism is reasonably discussed based on the experimental and theoretical results. This study opens up novel perspectives for preparing ultrathin and large-area MOF membranes using the solution processability of MOFs.

Prominent Size Effects without a Depolarization Field Observed in Ultrathin Ferroelectric Oxide Membranes.

The increasing miniaturization of electronics requires a better understanding of material properties at the nanoscale. Many studies have shown that there is a ferroelectric size limit in oxides, below which the ferroelectricity will be strongly suppressed due to the depolarization field, and whether such a limit still exists in the absence of the depolarization field remains unclear. Here, by applying uniaxial strain, we obtain pure in-plane polarized ferroelectricity in ultrathin SrTiO_{3} membranes, providing a clean system with high tunability to explore ferroelectric size effects especially the thickness-dependent ferroelectric instability with no depolarization field. Surprisingly, the domain size, ferroelectric transition temperature, and critical strain for room-temperature ferroelectricity all exhibit significant thickness dependence. These results indicate that the stability of ferroelectricity is suppressed (enhanced) by increasing the surface or bulk ratio (strain), which can be explained by considering the thickness-dependent dipole-dipole interactions within the transverse Ising model. Our study provides new insights into ferroelectric size effects and sheds light on the applications of ferroelectric thin films in nanoelectronics.

Structure Regulation of MOF Nanosheet Membrane for Accurate H2/CO2 Separation

AbstractHigh‐purity H2 production accompanied with a precise decarbonization opens an avenue to approach a carbon‐neutral society. Metal–organic framework nanosheet membranes provide great opportunities for an accurate and fast H2/CO2 separation, CO2 leakage through the membrane interlayer galleries decided the ultimate separation accuracy. Here we introduce low dose amino side groups into the Zn2(benzimidazolate)4 conformation. Physisorbed CO2 served as interlayer linkers, gently regulated and stabilized the interlayer spacing. These evoked a synergistic effect of CO2 adsorption‐assisted molecular sieving and steric hinderance, whilst exquisitely preserving apertures for high‐speed H2 transport. The optimized amino membranes set a new record for ultrathin nanosheet membranes in H2/CO2 separation (mixture separation factor: 1158, H2 permeance: 1417 gas permeation unit). This strategy provides an effective way to customize ultrathin nanosheet membranes with desirable molecular sieving ability.

Structure Regulation of MOF Nanosheet Membrane for Accurate H2 /CO2 Separation.

High-purity H2 production accompanied with a precise decarbonization opens an avenue to approach a carbon-neutral society. Metal-organic framework nanosheet membranes provide great opportunities for an accurate and fast H2 /CO2 separation, CO2 leakage through the membrane interlayer galleries decided the ultimate separation accuracy. Here we introduce low dose amino side groups into the Zn2 (benzimidazolate)4 conformation. Physisorbed CO2 served as interlayer linkers, gently regulated and stabilized the interlayer spacing. These evoked a synergistic effect of CO2 adsorption-assisted molecular sieving and steric hinderance, whilst exquisitely preserving apertures for high-speed H2 transport. The optimized amino membranes set a new record for ultrathin nanosheet membranes in H2 /CO2 separation (mixture separation factor: 1158, H2 permeance: 1417 gas permeation unit). This strategy provides an effective way to customize ultrathin nanosheet membranes with desirable molecular sieving ability.

Ultra-Fast Preparation of Large-Area Graphdiyne-Based Membranes via Alkynylated Surface-Modification for Nanofiltration.

Graphdiynes (GDYs), two-dimensional graphene-like carbon systems, are considered as potential advanced membrane material due to their unique physicochemical features. Nevertheless, the scale-up of integrated GDY membranes is technologically challenging, and most studies remain at the theoretical stage. Herein, we report a simple and efficient alkynylated surface-mediated strategy to prepare hydrogen-substituted graphdiyne (HsGDY) membranes on commercial alumina tubes. Surface alkynylation initiates an accelerated surface-confined coupling reaction in the presence of a copper catalyst and facilitates the nanoscale epitaxial lateral growth of HsGDY. A continuous and ultra-thin HsGDY membrane (∼100 nm) can be produced within 15 min. The resulting membranes exhibit outstanding molecular sieving together with excellent water permeances (ca. 1100 L m-2 h-1 MPa-1 ), and show a long-term durability in cross-flow nanofiltration, owing to the superhydrophilic surface and hydrophobic pore walls.

Ultrathin ionic COF Membrane via Polyelectrolyte‐Mediated Assembly for Efficient CO2 Separation

AbstractFabricating ultrathin covalent organic framework (COF) membranes toward high‐permeance molecular separations is highly desired yet challenging. Herein, a polyelectrolyte‐mediated assembly (PMA) strategy is developed to fabricate ultrathin ionic COF membrane for efficient CO2 separation. The PMA strategy allows a facile control over the assembly mode between polyethyleneimine (PEI) and TpPa‐SO3H, yielding PEI‐bridged ultra‐large COF nanosheets which are readily processed into COF membranes with thickness down to 8 nm. The resulting COF membranes exhibit a high CO2 permeances of 1371 GPU and CO2/N2 selectivity of 33 for stimulated flue gas. This PMA strategy may open up a new avenue to fabricating ultrathin 2D material membranes for diverse applications.

Comprehensive characterization of gas diffusion through graphene oxide membranes

Graphene oxide (GO) based multi-layered membranes have shown outstanding molecular-sieving properties for gas separation, surpassing the upper bound for polymeric membranes especially for hydrogen decarbonization. At the same time, the mechanism of gas permeation through such 2D GO membranes is very different in comparison to the traditional polymeric membranes due to multilayer, laminated nature of the former. For strategical design of novel membranes based on two-dimensional materials, it is important to understand the mechanism and to be able to measure two key parameters for gas transport: diffusivity and solubility. Such measurements are well established for the characterization of transport properties of bulk polymeric membranes. However, it is still a challenge to measure gas diffusion coefficients directly and accurately in ultra-thin multi-layered membranes. The lack of characterization limits our understanding of the mechanisms of gas transport though such membranes. In this work, we applied a time-lag method to determine the diffusivities for He, H2, O2, N2, CH4, CO2 and H2/CO2 equimolar mixture by on-line mass spectrometry. In contrast to polymeric membranes, the diffusivity and diffusion activation energy for all gases in 2D membranes are exponentially dependent on pathway length. Thus, in 2D membrane we can use an easy strategy to precisely regulate permeability and selectivity by the adjustment of the number of nanolayers and the size of 2D flakes, which is not possible using traditional polymeric membranes. This study is important for both the characterization and the standardization of gas transport properties of multi-layered membranes, and the design of novel membranes based on 2D materials.

Swelling dynamics and chain structure of ultrathin PEG membranes in seawater

Polyethylene glycol (PEG) is widely utilized in marine antifouling materials; thus, the fundamental understanding of PEG characteristics in seawater is indispensable. Herein, a “membrane-seawater” separation chamber model is designed, and the molecular dynamics (MD) method is used to simulate the swelling process of PEG membranes in seawater; two characteristic lengths are developed from the concept of Gibbs surface to illustrate the relationship between seawater ions and PEG membranes; the amount of bound water in the hydration shell of PEG is calculated by experimental method. It is concluded that the water content of the PEG membrane in seawater is not much different from that of swelling in water; only the swelling rate changes; the seawater ions accelerate the swelling of the PEG membrane, but most gathered in the outer layer of PEG membrane; Ions change the distribution structure of the hydration layer, and the bound water of PEG decreases under the action of seawater ions. Moreover, the structure of the PEG chain in seawater has a change of “helix-ring”. The study of PEG in seawater will provide an effective supplement and theoretical basis for the modification design of PEG coating.

Ultra-long-life and ultrathin quasi-solid electrolytes fabricated by solvent-free technology for safe lithium metal batteries

The excessive consumption of organic solvent and enhancement of environmental protection protocols necessitate the exploitation of desirable approach to handle our solid-state electrolytes. Herein, we report an all solvent-free method for the preparation of low-cost, recyclability, flexible, ultrathin, and high ionic conductivity quasi-solid polymer electrolytes (QPE) membrane, which is an 5 μm-thick PE separators filled with polyether-block-polyamide (PEO-b-PA6)/LiTFSI/tetraethylene glycol dimethyl ether (TEGDME) (PPLT) that can be used as a safe lithium metal batteries. The self-fusion characteristics of the PEO-b-PA6 with supramolecular hydrogen bonds guarantees the intimate and perfect interfaces even during extreme deformations and crack of the solvent-free machining process. The ultrathin PE separators is mechanically strong, preventing batteries from short-circuiting even after more than 1200 h of cycling, and the ionic conductivity of PPLT reaches up to 1.02 × 10−4 S cm−1 at 30 ℃ by adding only 25 wt% of TEGDME as plasticizer. The LFP//Li cells using PPLT as electrolyte exhibits excellent reversible capacity of 116 mAh g−1 at 1 C after 700 cycles at 28 °C. In addition, the polymer soft-pack batteries using PPLT achieve highly reversible capacity of 124.9 mAh g−1 after 200 cycles at 0.2 C. It is noted that this solvent-free film-making process and outstanding electrochemical performance of this QPE could be further delivered to other room temperature rechargeable solid-state lithium metal batteries and enlighten safe, low-carbon green and high-energy solid-state batteries.

Lipoic Acid-Assisted In Situ Integration of Ultrathin Solid-State Electrolytes

Ultrathin solid-state electrolytes (SSEs) have contributed to high-energy-density lithium-ion batteries (LIBs). However, when reducing thickness of SSEs, mechanical properties will inevitably deteriorate, even increasing the safety hazards. In this work, we developed an in-situ integration strategy to form an ultrathin SSE by combining a lipoic acid-assisted semi-interpenetrating polymer network and an ultrathin porous membrane. With this strategy, the thickness of the obtained SSE (named LA-SSE) is only 10 μm, and the LA-SSE possesses extraordinary mechanical performances to suppress the growth of lithium dendrites. Meanwhile, the flexible LA-SSE presents anionic conductivity of 0.036 mS cm–1 and promotes interfacial compatibility between the lithium anode and the electrolyte. By employing LA-SSE as the electrolyte, the assembled Li∥LA-SSE∥Li symmetric cell operated with long-term cycling (more than 3000 h), and the LiFePO4∥LA-SSE∥Li full battery worked steadily over 200 cycles at 0.5 C with a capacity retention of 84% at room temperature. This work provides a promising strategy for designing ultrathin SSEs, with satisfactory mechanical properties, excellent interfacial compatibility, and safety, for LIBs.

Sub-two-micron ultrathin proton exchange membrane with reinforced mechanical strength

Proton exchange membranes (PEM) serve as indispensable components in fuel cells, flow batteries, and other electrochemical applications. Over the past six decades, PEMs of diverse compositions and structures have been developed for various industrial scenarios. Among all parameters, the thickness is pivotal in affecting the performance, cost, and stability of PEM. Yet for either pure or composite PEM, there is a lower boundary of thickness if the PEM is still targeted to practical utilization. As there is a trade-off between thickness and mechanical stability for a freestanding membrane. We selected ultra-high molecular weight polyethylene (UHMWPE) for its outstanding processability and high modulus intrinsically to breakthrough this trade-off. By biaxially stretching UHMWPE into ∼300 nm thin porous membranes and impregnating Nafion interiorly, with careful interfacial engineering, a type of ∼1.6-μm thin composite PEM was prepared. As the thinnest freestanding PEM with practical use ever reported, surficial, cross-sectional, and interfacial structures were rigorously characterized to explain its performance. In the end, this thin PEM demonstrated a membrane power density of up to 663.69 mW cm−2 for H2–O2 fuel cell set-up. This work provides new insight into the structure-performance correlation of PEM with a near-sub-micron thickness. And it may also inspire future research to further address the performance-stability paradox of PEM with thin/ultrathin thickness range.

A Study on the Synthesis and Proton Transport Behavior of Multilayered ZSM-5 Zeolite Nanosheet Membranes Laminated on Polymer Substrates

Single crystalline ZSM-5 ZNs with thicknesses around 6 nm were obtained by secondary growth of silicalite nanoparticles using diquaternary bis-1,5(tripropyl ammonium) pentamethylene diiodide (dC5) as a structure-directing agent (SDA). The dC5 could be effectively removed from the ZN pores by either high-temperature calcination or UV irradiation in air at room temperature but not by the piranha solution treatment. Ultrathin ZN-laminated membranes (ZNLMs) were fabricated by sandwiching a UV-activated multilayered ZN film between two recast Nafion® layers (ZNLM-Nafion) and by filtration coating from a suspension of thermally activated ZNs on a nonionic porous PVDF (ZNLM-PVDF). The ZNLMs on both supports demonstrated the ability of highly proton-selective ion conduction with low resistances in aqueous electrolyte solutions. The ZNLM-PVDF with PVDF binder was structurally stable, and it achieved a comparably low ASR but much higher proton selectivity compared with a Nafion membrane of same overall thickness. However, detachment between the ZNLM and Nafion layers occurred when the ZNLM-Nafion operated in aqueous electrolyte solutions. Results of this study show the potential for developing ZNLMs as efficient proton-conducting membranes without using expensive ionic polymer matrices. However, the development of polymer-supported ZNLMs is hindered by the current inefficiency in preparing well-dispersed suspensions of open-pore ZNs. Future development of efficient methods for synthesizing open-pore ZNs in dispersed states is key to realizing high-performance ZNLMs on polymers.

A multiplex inhalation platform to model in situ like aerosol delivery in a breathing lung-on-chip.

Prolonged exposure to environmental respirable toxicants can lead to the development and worsening of severe respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD) and fibrosis. The limited number of FDA-approved inhaled drugs for these serious lung conditions has led to a shift from in vivo towards the use of alternative in vitro human-relevant models to better predict the toxicity of inhaled particles in preclinical research. While there are several inhalation exposure models for the upper airways, the fragile and dynamic nature of the alveolar microenvironment has limited the development of reproducible exposure models for the distal lung. Here, we present a mechanistic approach using a new generation of exposure systems, the Cloud α AX12. This novel in vitro inhalation tool consists of a cloud-based exposure chamber (VITROCELL) that integrates the breathing AXLung-on-chip system (AlveoliX). The ultrathin and porous membrane of the AX12 plate was used to create a complex multicellular model that enables key physiological culture conditions: the air-liquid interface (ALI) and the three-dimensional cyclic stretch (CS). Human-relevant cellular models were established for a) the distal alveolar-capillary interface using primary cell-derived immortalized alveolar epithelial cells (AXiAECs), macrophages (THP-1) and endothelial (HLMVEC) cells, and b) the upper-airways using Calu3 cells. Primary human alveolar epithelial cells (AXhAEpCs) were used to validate the toxicity results obtained from the immortalized cell lines. To mimic in vivo relevant aerosol exposures with the Cloud α AX12, three different models were established using: a) titanium dioxide (TiO2) and zinc oxide nanoparticles b) polyhexamethylene guanidine a toxic chemical and c) an anti-inflammatory inhaled corticosteroid, fluticasone propionate (FL). Our results suggest an important synergistic effect on the air-blood barrier sensitivity, cytotoxicity and inflammation, when air-liquid interface and cyclic stretch culture conditions are combined. To the best of our knowledge, this is the first time that an in vitro inhalation exposure system for the distal lung has been described with a breathing lung-on-chip technology. The Cloud α AX12 model thus represents a state-of-the-art pre-clinical tool to study inhalation toxicity risks, drug safety and efficacy.

Constructing 2D ultrathin graphene oxide membranes with supramolecular-assembled nano-adhesives for enhancing water stability

Constructing 2D ultrathin graphene oxide membranes with supramolecular-assembled nano-adhesives for enhancing water stability

Fabrication of Highly Oriented Ultrathin Zirconium Metal-Organic Framework Membrane from Nanosheets towards Unprecedented Gas Separation.

Concurrent regulation of crystallographic orientation and thickness of zirconium metal-organic framework (Zr-MOF) membranes is challenging but promising for their performance enhancement. In this study, we pioneered the fabrication of uniform triangular-shaped, 40 nm thick UiO-66 nanosheet (NS) seeds by employing an anisotropic etching strategy. Through innovating confined counter-diffusion-assisted epitaxial growth, highly (111)-oriented 165 nm-thick UiO-66 membrane was prepared. The significant reduction in thickness and diffusion barrier in the framework endowed the membrane with unprecedented CO2 permeance (2070 GPU) as well as high CO2 /N2 selectivity (35.4), which surpassed the performance limits of state-of-the-art polycrystalline MOF membranes. In addition, highly (111)-oriented 180 nm-thick NH2 -UiO-66 membrane showing superb H2 /CO2 separation performance with H2 permeance of 1230 GPU and H2 /CO2 selectivity of 41.3, was prepared with the above synthetic procedure.

Ultrathin bimodal porous membranes with uniform small pores separated by laminated large pores for efficient water separation

Bimodal pore structure design of separation membranes is a promising way to simultaneously improve permeability and selectivity. However, the thickness limitation of bimodal porous membranes is an obstacle to further improving the separation efficiency. In this study, a novel bimodal porous structure with uniform small pores on the surface and a unique laminated large pore structure in the thickness direction was successfully constructed through biaxial stretching of gel films in ultra-high molecular weight polyethylene membranes. With an increase in the draw ratio to 12 × 12, the uniformly refined small pores increased the rejection rate of the carbon nanoparticle solution (particle size distribution of 60–400 nm) to 99.4%, and the unique laminated large pore structure enabled the permeance to reach 1141.8 L m-2h−1 bar−1. By further increasing the draw ratio to 16 × 16, the membrane thickness decreased to 0.91 μm and the permeance was further increased to 2008.2 L m-2h−1 bar−1 while the selectivity slightly decreased to 98.9%. Furthermore, a bimodal porous membrane with sufficient strength (237 MPa of 16 × 16) was efficient for long-term water separation. This study proposes a new design idea for ultrathin porous membranes, which can be further expanded to prepare various antifouling, self-cleaning, and multifunctional separation membranes.

Highly porous ultrathin polyamide membranes for fast separation of small molecules from organic solvents

Membranes with permselective performance as well as high stability in harsh solvents are urgently desired for energy-efficient precise chemical separations. In this work, we utilize an adamantane diamine as a molecular building block to fabricate thin-film composite polyamide membranes for high-performance organic solvent nanofiltration (OSN). The bulky, cage-like adamantane structure acts as a molecular-level steric hindrance unit to inhibit polymer chain packing which generating interconnected micropores within the interfacially polymerized polyamide layer. This translates into high membrane methanol permeance of 20.6 L m-2 h-1 bar-1 and 94.7% retention to organic dye molecules with molecular weight down to 327 g mol-1. Furthermore, the membrane demonstrates high stability in different organic solvents taking advantage of the crosslinked rigid structure, which shows constant solute retention throughout a 180 h continuous filtration experiment with a DMF solution containing methyl orange as feed solution. Employing rigid and bulky molecular features in selective layer is thus demonstrated to significantly promote the polyamide membrane permeability and solvent resistance without compromising the overall selectivity.

Templated Synthesis of Diamond Nanopillar Arrays Using Porous Anodic Aluminium Oxide (AAO) Membranes

Diamond nanostructures are mostly produced from bulk diamond (single- or polycrystalline) by using time-consuming and/or costly subtractive manufacturing methods. In this study, we report the bottom-up synthesis of ordered diamond nanopillar arrays by using porous anodic aluminium oxide (AAO). Commercial ultrathin AAO membranes were adopted as the growth template in a straightforward, three-step fabrication process involving chemical vapor deposition (CVD) and the transfer and removal of the alumina foils. Two types of AAO membranes with distinct nominal pore size were employed and transferred onto the nucleation side of CVD diamond sheets. Subsequently, diamond nanopillars were grown directly on these sheets. After removal of the AAO template by chemical etching, ordered arrays of submicron and nanoscale diamond pillars with ~325 nm and ~85 nm diameters were successfully released.