Track-etched Membranes Research Articles

Robust, High-Temperature-Resistant Polyimide Separators with Vertically Aligned Uniform Nanochannels for High-Performance Lithium-Ion Batteries.

Separator is an essential component of lithium-ion batteries (LIBs), playing a pivotal role in battery safety and electrochemical performance. However, conventional polyolefin separators suffer from poor thermal stability and nonuniform pore structures, hindering their effectiveness in preventing thermal shrinkage and inhibiting lithium (Li) dendrites. Herein, we present a robust, high-temperature-resistant polyimide (PI) separator with vertically aligned uniform nanochannels, fabricated via ion track-etching technology. The resultant PI track-etched membranes (PITEMs) effectively homogenize Li-ion distribution, demonstrating enhanced ionic conductivity (0.57 mS cm-1) and a high Li+ transfer number (0.61). PITEMs significantly prolong the cycle life of Li/Li cells to 1200 h at 3 mA cm-2. For Li/LiFePO4 cells, this approach enables a specific capacity of 143 mAh g-1 and retains 83.88% capacity after 300 cycles at room temperature. At 80 °C, the capacity retention remains at 85.92% after 200 cycles. Additionally, graphite/LiFePO4 pouch cells with PITEMs display enhanced cycling stability, retaining 73.25% capacity after 1000 cycles at room temperature and 78.41% after 100 cycles at 80 °C. Finally, PITEMs-based pouch cells can operate at 150 °C. This separator not only addresses the limitations of traditional separators, but also holds promise for mass production via roll-to-roll methods. We expect this work to offer insights into designing and manufacturing of functional separators for high-safety LIBs.

Adaptable Plasmonic Membrane Sensors for Fast and Reliable Detection of Trace Low-Micrometer Microplastics in Lake Water.

In freshwater environments, low-micrometer microplastics (LMMPs) have captured significant attention due to their prevalence and toxicity. Yet, rapid detection of LMMPs (1-10 μm) at the single-particle level within complex freshwater matrices remains a hurdle. We developed an adaptable plasmonic membrane sensor for fast detection of individual LMMPs in eutrophic lake waters. The plasmonic membrane sensor functions both as a membrane filter and as a sensor for LMMP collection and analysis. Among the four types of membrane sensors, polycarbonate track-etch (PCTE) membrane sensors exhibit superior imaging quality for LMMPs due to their flat and homogeneous surfaces. Besides the significantly improved imaging contrast and reduced background interferences, the Raman intensity of LMMPs is enhanced by 48% ± 25% on PCTE membrane sensors compared to unmodified membranes. The increased Raman intensities of a chemical probe with an increasing gold layer thickness and a decreasing membrane pore size suggest a surface-enhanced Raman scattering effect from the membrane sensors. The membrane sensors achieve a detection limit of 1 μg/L and an ultrafast scanning time of 0.01 s for individual LMMPs across natural eutrophic lake water. The developed membrane sensors offer an adaptable tool for the swift and reliable detection of individual LMMPs in complex environmental matrices.

Formation of Hydrophobic Coatings on the Surface of Track-Etched Membranes Using Magnetron Sputtering of Polymers in Vacuum

Formation of Hydrophobic Coatings on the Surface of Track-Etched Membranes Using Magnetron Sputtering of Polymers in Vacuum

Composite Track-Etched Membranes: Synthesis and Multifaced Applications.

Composite track-etched membranes (CTeMs) emerged as a versatile and high-performance class of materials, combining the precise pore structures of traditional track-etched membranes (TeMs) with the enhanced functionalities of integrated nanomaterials. This review provides a comprehensive overview of the synthesis, functionalization, and applications of CTeMs. By incorporating functional phases such as metal nanoparticles and conductive nanostructures, CTeMs exhibit improved performance in various domains. In environmental remediation, CTeMs effectively capture and decompose pollutants, offering both separation and detoxification. In sensor technology, they have the potential to provide high sensitivity and selectivity, essential for accurate detection in medical and environmental applications. For energy storage, CTeMs may be promising in enhancing ion transport, flexibility, and mechanical stability, addressing key issues in battery and supercapacitor performance. Biomedical applications may benefit from the versality of CTeMs, potentially supporting advanced drug delivery systems and tissue engineering scaffolds. Despite their numerous advantages, challenges remain in the fabrication and scalability of CTeMs, requiring sophisticated techniques and meticulous optimization. Future research directions include the development of cost-effective production methods and the exploration of new materials to further enhance the capabilities of CTeMs. This review underscores the transformative potential of CTeMs across various applications and highlights the need for continued innovation to fully realize their benefits.

Microdialysis-integrated HPLC system with dual-electrode detection using track-etched membrane electrodes for in vivo monitoring of dopamine dynamics

A capillary high-performance liquid chromatography (HPLC) system equipped with a dual-electrode detector utilizing track-etched membrane electrodes (TEMEs) was combined with a microdialysis sampling setup. The electrochemical detector benefits from the high electrolysis efficiency of TEMEs, allowing for calibration-free coulometric detection and simplifying data analysis to determine the dopamine recovery through a dialysis probe. Additionally, this system was used for in vivo monitoring of dopamine in the right striatum of a mouse brain. Temporal changes in dopamine levels, including an exponential decay immediately after the dialysis probe insertion and an excess release of dopamine induced by a high concentration of potassium ions, confirmed the system’s proper operation. Furthermore, subsequent measurements following the intraperitoneal injection of mirtazapine showed no increase in dopamine levels in the right dorsal striatum. The dual-electrode system displayed characteristic dopamine detection behavior, with anodic and cathodic peak pairs indicative of reversible electrochemical reactions. This capability facilitated the identification of the dopamine peak within the complex chromatogram of the mouse brain dialysate. The consistency between dopamine collection efficiency from standard solutions and dialysate indicated the absence of interfering electroactive substances overlapping with the dopamine peak in the chromatogram. This integrated analysis system successfully tracked temporal fluctuations in dopamine concentration within the mouse brain.

The effect of pore boundary shape on the performance of catalytic self-pumping membranes and channels

Many technologies demand highly controllable membranes, including lab-on-a-chip systems, microfluidic sensors, and electrochemical cells. The pumps for these systems can be scaled down by many orders of magnitude with electrochemical pumps, and more still with recently invented membrane pumps. Such pumps have been demonstrated to independently pump fluid via catalytic reactions that create and consume H+ cations on opposite sides of the membrane. Our prior work showed that the mechanism behind this phenomenon was a self-generated electric field driving the fluid flow caused by the space charge polarization due to the electrochemical reactions. However, that work assumed that the pores inside a membrane were perfectly cylindrical, which is not always true. This work investigates more complicated and realistic structures that deviate from a perfectly cylindrical shape, as is typical of actual track-etched or polymeric membranes. The pore structures were studied using a 2D model, which solved the Poisson-Nernst-Planck-Stokes equations in COMSOL 5.5. Based on our previously validated model, we examine the impact of different parameters on self-pumping flow rates, including pore width, contracting/expanding variation, pore length, and pore inclination angle. According to the results, the self-pumping flow rate is more sensitive to pore width than pore length. Regarding the effects of pore defects, membranes with complicated shapes of contracting/expanding pores and cross-linked connecting pores should follow the same pattern as those membranes with straight pores and similar pore size; likewise, pore inclination does not significantly influence self-pumping flow. Therefore, the conclusions we obtained for cylindrical straight pores are still applicable. The results highlight the potential of utilizing catalytic reactions to manipulate liquid via actual track-etched membranes.

A Novel Method for Separating Full and Empty Adeno-Associated Viral Capsids Using Ultrafiltration.

Adeno-associated viral vectors (AAVs) are the predominant viral vectors used for gene therapy applications. A significant challenge in obtaining effective doses is removing non-therapeutic empty viral capsids lacking DNA cargo. Current methods for separating full (gene-containing) and empty capsids are challenging to scale, produce low product yields, are slow, and are difficult to operationalize for continuous biomanufacturing. This communication demonstrates the feasibility of separating full and empty capsids by ultrafiltration. Separation performance was quantified by measuring the sieving coefficients for full and empty capsids using ELISA, qPCR, and an infectivity assay based on the live cell imaging of green fluorescent protein expression. We demonstrated that polycarbonate track-etched membranes with a pore size of 30 nm selectively permeated empty capsids to full capsids, with a high recovery yield (89%) for full capsids. The average sieving coefficients of full and empty capsids obtained through ELISA/qPCR were calculated as 0.25 and 0.49, indicating that empty capsids were about twice as permeable as full capsids. Establishing ultrafiltration as a viable unit operation for separating full and empty AAV capsids has implications for developing the scale-free continuous purification of AAVs.

Effect of external electric fields on the ionic conductivity of the PET ion-track membrane

Polymeric ion track-etched membranes with asymmetric pores have been the subject of increased interest in both the academia and industry in recent decades. This interest is related to the rectification behavior of the membranes and their possible applications. In this work, the polyethylene terephthalate (PET) membranes with conical ion tracks were investigated for different etching conditions. Thin PET membranes were prepared using irradiated foils etched in a NaOH bath with the help of external electric fields (AC/DC) of a specific polarity. After etching, the I-V characteristics of the membranes were examined in the KCl solutions with different molarities. The obtained results showed that the I-V relations are strongly non-linear, thus confirming the rectification behavior of the membranes. It turned out that the external AC and DC fields applied during etching play an important role. They make it possible to influence the pore etching process, and so the properties of the membranes, which is important for the intended applications. Keywords: polymeric membranes, asymmetric pores, polyethylene terephthalate, I-V characteristics, transport phenomena

Enhancing virus inhibition in track-etched membranes through surface modification with silver nanoparticles and curcumin

The present work reports on the use of silver nanoparticles (AgNPs) and curcumin immobilized on the surface of microfiltration track-etched membranes (mTMs) as antiviral filtration materials. AgNPs were synthesized through the direct reduction of silver nitrate by sodium borohydride in the presence of a stabilizing agent. The synthesized nanoparticles and curcumin were immobilized on polyethyleneimine (PEI)-modified mTMs through a static sorption process. TEM, SEM, UV–vis. spectroscopy and luminescence measurements revealed a uniform distribution of AgNPs and confirmed the presence of curcumin on the membrane surface. The resulting TM-PEI-AgNPs-PVP and TM-PEI-Curcumin hybrid membranes were employed for the filtration of HSV-1, VSV, IAV, and EMCV viruses. While both membrane types exhibited insignificant inhibition for the latter two, they achieved 95 and 99 % inhibition for HSV-1 and VSV, respectively. These findings suggest that hybrid membranes with immobilized AgNPs and curcumin can have potential as antiviral filtration materials.

Fabrication of Two-Layer Microfluidic Devices with Porous Electrodes Using Printed Sacrificial Layers.

Two-layer microfluidic devices with porous membranes have been widely used in bioapplications such as microphysiological systems (MPS). Porous electrodes, instead of membranes, have recently been incorporated into devices for electrochemical cell analysis. Generally, microfluidic channels are prepared using soft lithography and assembled into two-layer microfluidic devices. In addition to soft lithography, three-dimensional (3D) printing has been widely used for the direct fabrication of microfluidic devices because of its high flexibility. However, this technique has not yet been applied to the fabrication of two-layer microfluidic devices with porous electrodes. This paper proposes a novel fabrication process for this type of device. In brief, Pluronic F-127 ink was three-dimensionally printed in the form of sacrificial layers. A porous Au electrode, fabricated by sputtering Au on track-etched polyethylene terephthalate membranes, was placed between the top and bottom sacrificial layers. After covering with polydimethylsiloxane, the sacrificial layers were removed by flushing with a cold solution. To the best of our knowledge, this is the first report on the sacrificial approach-based fabrication of two-layer microfluidic devices with a porous electrode. Furthermore, the device was used for electrochemical assays of serotonin and could successfully measure concentrations up to 5 µM. In the future, this device can be used for MPS applications.

Lithium recycling from artificial leachate of spent lithium-ion batteries using track-etched membranes for hybrid electrobaromembrane method

Lithium recycling is still poorly developed, but an important source of raw materials for the production of lithium salts. The hydrometallurgical technologies are usually employed to extract lithium from spent lithium-ion batteries. Reagent free membrane technologies such as electrobaromembrane method (EBM) can be used at this stage for the separation of Li+ ions and Co2+, Ni2+, Mn2+. The essence of the method is the simultaneous use of an opposing electric field and a pressure gradient in the device. Non-selective track-etched membrane with wide pores is used for ions separation. The selectivity of EBM separation is achieved due to the different mobility of the separated ions in the electric field. Under optimal conditions, this allows some of the more mobile ions to overcome the barrier of the oncoming convective flow, while others follow it. For the first time, the EBM method was used for long-term extraction of Li+ ions from an artificial leachate solution of spent LIBs. A solution containing the main macro components of typical leachate was processed at 0.3 bar and 125 A/m2 for 50 h. The fluxes of separated Li+, Co2+, Ni2+ and Mn2+ ions through the track-etched membrane were as follows 0.2, −0.02, −0.03 and − 0.08 mol/(m2 × h), respectively. A modification of the track-etched membrane with PDADMAC, which carries a positive charge, has been approved, which makes it possible to increase the rejection of doubly charged ions for more effective lithium isolation.

Covalent Organic Framework-Coated Polyimide Ion-Track-Etched Separator with High Thermal Stability for Developing Lithium-Ion Batteries with Long Lifespans.

Separators play a crucial role in inhibiting thermal runaway in lithium-ion batteries (LIBs). In this study, the doctor blade coating method and heavy-ion track etching technology were used to prepare a polyimide-based covalent organic framework (PI_COF) separator with excellent thermal stability and a long cycle life. Specifically, COF300 was simply coated on the surface of a polyimide-based track-etched membrane (PI_TEM) with straight through holes, which provided a rigid framework and high-temperature stability at 300 °C. These features were conducive to inhibiting thermal runaway, while porous COF300 with large holes increased the wettability of the electrolyte, facilitating lithium-ion migration and suppression of lithium dendrite growth; consequently, LIBs with an excellent cycling performance and a high rate capacity were obtained. The cell with the PI_COF separator delivered a high capacity of 90.0 mA h g-1 after 1000 cycles. The PI_COF separator with high thermal stability exhibited a long cycle life in LIBs. These features are beneficial for improving the safety characteristics of LIBs as well as for accelerating the practical application process of the PI_COF separator.

Surface Modification of Polyethylene Terephthalate Track-Etched Membranes by 2,2,3,3,4,4,5,5,6,6,7,7-Dodecafluoroheptyl Acrylate for Application in Water Desalination by Direct Contact Membrane Distillation.

In this work, the surfaces of poly (ethylene terephthalate) track-etched membranes (PET TeMs) with pore sizes of 670-1310 nm were hydrophobized with 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl acrylate (DFHA) by photoinitiated graft polymerization. Attenuated total reflection FTIR spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray spectrometer (EDX), and contact angle measurements were used to identify and characterize the TeMs. The optimal parameters for graft polymerization were determined as follows: polymerization time of 60 min, monomer concentration of 30%, and distance from the UV source of 7 cm. The water contact angle of the modified membranes reached 97°, which is 51° for pristine membranes. The modified membranes were tested for water desalination using direct contact membrane distillation (DCMD) method. The effects of membrane pore size, the degree of grafting, and salt concentration on the performance of membrane distillation process were investigated. According to the results obtained, it has been concluded that large pore size hydrophobic TeMs modified by using DFHA could be used for desalinating water.

Liquid gated membrane with self-cleaning properties for controllable removal and multi-component separation of organic/bacterial contaminants

Membrane technology plays an important role in sustainable water treatment; however, the non-adjustable pores make it difficult to achieve precise molecular separation, and membrane fouling remains a challenge in membrane processes. Herein, a smart liquid gated membrane (LGM) was prepared by filling different lubricants in the micropores of PET track-etched membrane that was pre-treated with nano roughening and fluorination. When the pressure exceeds a critical breakthrough pressure, the liquid lined pores are formed, and higher gating liquid/water interfacial tension requires higher pressure to break through the gate. The effective pore size of LGM increases with increasing pressure. When the pressure is removed, the liquid refilling that leads to pore-closing is promoted by lower lubricant viscosity and larger effective pore size. Through the tunable permeability, controllable removal and multi-component separation of organic/bacterial contaminants can be achieved. The maximum rejection for protein approaches 94 %; as the pressure increases, three components are separated in the order of pectin, soy protein isolate and Staphylococcus aureus with maximum separation coefficient of 56.7. Due to the stable lubricant lining, LGM shows excellent self-cleaning performance with much higher flux recovery rate than the non-lubricated membranes. This liquid gated membrane has great application prospects in size-fractionated separation and product recovery.

Ion transport across bilayer lipid membranes using a track-etched membrane filter

Bilayer lipid membranes (BLM) are widely employed to study the electrochemical behavior across cell membranes, particularly the ion transport in the presence of hydrophobic ions or ionophores. However, owing to the physical fragility of BLMs, they are readily broken down by external shocks, such as the applications of a potential difference, current, and vibration. Thus, in this study, a facile method for enhancing the physical stability of BLMs was developed using a track-etched membrane (TM). Physically stable BLMs were rapidly fabricated within the apertures of TM by dropping an n-decane solution containing lecithin and cholesterol on TM. Therefore, BLM formation was confirmed by capacitance measurement, and the estimated membrane thickness and mean capacitance were 3.5 ± 0.4 nm and 0.51 ± 0.05 μF cm−2, respectively. The applied membrane potential could be extended to ≥1.5 V, which is approximately 10 times higher than those of conventional BLMs, and the lifetime exceeded 40 min. The applicability of the fabricated BLM was verified by electrochemical measurements during ion transport.

Modification of Track-Etched Polyethylene Terephthalate Membranes with Functionalized Silanes for Immobilizing Silver Nanoparticles

Modification of Track-Etched Polyethylene Terephthalate Membranes with Functionalized Silanes for Immobilizing Silver Nanoparticles

Integration of 2D Nanoporous Membranes in Microfluidic Devices.

2D material-based membranes have emerged as promising candidates for next-generation separation technology due to their exceptional permeability and selectivity. Integration of these membranes into microfluidic devices has offered significant potential for improving the efficiency, throughput, and precision. However, designing compact and reliable microfluidic devices with membranes has many challenges, including complexities in membrane integration, analyte measurement, and contamination issues. Addressing these challenges is critical for unlocking the full potential of membrane-integrated devices. This paper proposes a systematic procedure for integrating membranes into a microfluidic device by creating a pore in the middle layer. Furthermore, an ion transport experiment is carried out across various stacked graphene and poly carbonate track etch membranes in an Ostemer-based device. The resulting device is capable of facilitating the concurrent measurement, a task that is cumbersome in standard macroscopic diffusion cells. The transparency and compactness of the microfluidic device allowed for the in situ and real-time optical characterization of analytes. The integration of microfluidic devices with 2D nanoporous membranes has enabled the incorporation of several analytical modalities, resulting in a highly versatile platform with numerous applications.

Isoporous Membrane Mediated Imprinting Mass Spectrometry Imaging for Spatially-Resolved Metabolomics and Rapid Histopathological Diagnosis.

Surface-assisted laser desorption/ionization (SALDI) mass spectrometry imaging (MSI) holds great value in spatial metabolomics and tumor diagnosis. Tissue imprinting on the SALDI target can avoid laser-induced tissue ablation and simplifies the sample preparation. However, the tissue imprinting process always causes lateral diffusion of biomolecules, thereby losing the fidelity of metabolite distribution on tissue. Herein, a membrane-mediated imprinting mass spectrometry imaging (MMI-MSI) strategy is proposed using isoporous nuclepore track-etched membrane as a mediating imprinting layer to selectively transport metabolites through uniform and vertical pores onto silicon nanowires (SiNWs) array. Compared with conventional direct imprinting technique, MMI-MSI can not only exclude the adsorption of large biomolecules but also avoid the lateral diffusion of metabolites. The whole time for MMI-based sample preparation can be reduced to 2min, and the lipid peak number can increase from 46 to 113 in kidney tissue detection. Meanwhile, higher resolution of MSI can be achieved due to the confinement effect of the pore channel in the diffusion of metabolites. Based on MMI-MSI, the tumor margins of liver cancer can be clearly discriminated and their different subtypes can be precisely classified. This work demonstrates MMI-MSI is a rapid, highly sensitive, robust and high-resolution technique for spatially-resolved metabolomics and pathological diagnosis.

Track-etched membrane as a thin substrate with straight pores to fabricate polyamide forward osmosis membrane

Controlling the internal concentration polarization in forward osmosis (FO) membranes by minimizing the substrate thickness is critical to enhancing the water flux. This study aimed to achieve the fabrication of an ultra-thin FO membrane by forming the polyamide (PA) active layer on a thin and straight-bore film, a so-called track-etched (TE) membrane. The polycarbonate TE membrane had a uniform pore size of 0.22 µm and a thickness of 25 µm. The PA active layer was successfully formed only by creating a thin m-phenylenediamine solution layer on the smooth TE membrane surface before interfacial polymerization. The TE- FO membrane with low porosity (14 %) provided a water flux of 21 L/m2h and a reverse salt flux of 8.0 g/m2h when evaluated with a 1.0 M NaCl draw solution. Further evaluations showed the potential of increasing water flux by increasing the TE substrate porosity (14 %) and reducing the apparent PA active layer thickness (504 nm). These results suggest the potential of achieving a high-water flux FO membrane using a thin TE substrate and ultimately improving the validity of FO membrane-based water treatment.

Fabrication of Breathable Multifunctional On-Skin Electronics Based on Tunable Track-Etched Membranes

Fabrication of Breathable Multifunctional On-Skin Electronics Based on Tunable Track-Etched Membranes