Variations In Membrane Thickness Research Articles

Computational Analysis of Permeance Prediction for Gas Separation Membrane Using Countercurrent Flow Model

Gas separation polymeric membranes have gained significant attention in various industries, including gas processing, petrochemicals, and environmental applications. Accurately predicting the permeance of these membranes is crucial for optimizing their design and performance. This paper presented a numerical prediction model for the permeance of a binary gas mixture under various process conditions, using only algebraic equations to minimize the calculation effort. The model considers input parameters such as feed and permeate flow rates, feed pressure, feed and permeate mole fraction, and membrane area. It demonstrates the behavior of permeance and selectivity in this study. The study also presented two case studies that utilize predicted selectivity to model counter-current flow and compare the results with experimental data from the literature. The first case study involves recovering helium from natural gas using an asymmetric high-flux membrane. The second case study separates air using nano-porous carbon as the membrane material. The numerical analysis successfully accurately predicted the permeance of gas separation polymeric membranes. The model accounted for variations in membrane thickness, feed composition, and operating conditions, providing valuable insights into the overall performance of the membrane system. It also allowed for the optimization of membrane design and operational parameters to enhance separation efficiency and productivity. The study showcased the effectiveness of numerical techniques in accurately predicting membrane performance. The developed model can be a valuable tool for membrane designers and engineers, enabling them to optimize the design and operation of gas separation systems.

SPR humidity dynamic monitoring method via PVA sensing membrane thickness variation and image processing techniques

Humidity monitoring is paramount in diverse applications, industrial, and medical applications. Surface Plasmon Resonance (SPR) is an optical detection technique capable of sensing various environmental parameters through changes in reflected optical spectra and has garnered significant attention. Typically, SPR sensing employs a single-point detection strategy with the sample at a fixed concentration to achieve optimal sensitivity, limiting its application in dynamic environmental testing. This study proposes an image-based SPR humidity monitoring method, integrating SPR with image processing, enabling dynamic parameter reconstruction, and achieving high responsiveness. Au-PVA is used as a sensing film. To attain the best sensing film thickness, sensing film thicknesses ranging from 94.0 nm to 243.3 nm were tested. Through optimizing film thickness and image data processing, high precision and dynamic responsiveness were achieved. Experimental results demonstrate a response time of 84 ms and an average relative prediction error of 1.57 % for the sensor. Our research holds significant promise for dynamic and accurate humidity detection.

Optimization Thickness of Photoanode Layer and Membrane as Electrolyte Trapping Medium for Improvement Dye-Sensitized Solar Cell Performance

Dye-Sensitized Solar Cells (DSSC) are photovoltaic devices that contain a dye that acts as a solar light acceptor. The use of dyesensitized solar cells to solve increasing energy demand and environmental problems still results in low efficiency values. In this study, optimization of DSSC components was carried out to increase DSSC efficiency by varying the thickness of the titanium dioxide (TiO2) semiconductor photoanode layer, polyvinylidene fluoride (PVDF) trap electrolyte membrane, and polyvinylidene fluoride nanofiber (PVDF NF) to obtain the optimum thickness. Scanning Electron Microscope (SEM) results of membrane thickness variation and titanium dioxide (TiO2) semiconductor photoanode coating showed the formation of nanofiber fibers composed of three-dimensional, porous, and diameter networks connected to the PVDF NF membrane. The increase in density and decrease in pore size, along with an increase in thickness and cracking as the TiO2 photoanode semiconductor layer increases, affect the electron transport rate of the DSSC. The higher particle density level will inhibit the electron transport rate, so it can reduce the efficiency of DSSC. The optimum thickness of the TiO2 semiconductor layer and PVDF NF electrolyte membrane of 0.20 mm and 0.35 mm can produce values, voltage, fill factor current density, and electrical efficiency of 500 mV, 2.7 x 10−3 mA.cm−2, 1.80%, and 2.40%, respectively.

Bilayer tension-induced clustering of the UPR sensor IRE1

The endoplasmic reticulum acts as a protein quality control center where a range of chaperones and foldases facilitates protein folding. IRE1 is a sensory transmembrane protein that transduces signals of proteotoxic stress by forming clusters and activating a cellular program called the unfolded protein response (UPR). Recently, membrane thickness variation due to membrane compositional changes have been shown to drive IRE1 cluster formation, activating the UPR even in the absence of proteotoxic stress. Here, we demonstrate a direct relationship between bilayer tension and UPR activation based on IRE1 dimer stability. The stability of the IRE1 dimer in a (50%DOPC-50%POPC) membrane at different applied bilayer tensions was analyzed via molecular dynamics simulations. The potential of mean force for IRE1 dimerization predicts a higher concentration of IRE1 dimers for both tensed and compressed ER membranes. This study shows that IRE1 may be a mechanosensitive membrane protein and establishes a direct biophysical relationship between bilayer tension and UPR activation.

Cholesterol-Induced Nanoscale Variations in the Thickness of Phospholipid Membranes.

Graphene-induced energy transfer (GIET) is a recently developed fluorescence-spectroscopic technique that achieves subnanometric optical localization of fluorophores along the optical axis of a microscope. GIET is based on the near-field energy transfer from an optically excited fluorescent molecule to a single sheet of graphene. It has been successfully used for estimating interleaflet distances of single lipid bilayers and for investigating the membrane organization of living mitochondria. In this study, we use GIET to measure the cholesterol-induced subtle changes of membrane thickness at the nanoscale. We quantify membrane thickness variations in supported lipid bilayers (SLBs) as a function of lipid composition and increasing cholesterol content. Our findings demonstrate that GIET is an extremely sensitive tool for investigating nanometric structural changes in biomembranes.

A New Standard for Membrane Structure? Investigating Factors that Influence Measured Bilayer Thickness in Cryo-EM Images

Cryogenic electron microscopy (cryo-EM) is a promising tool for the analysis of lipid bilayer structure. We recently showed that cryo-EM can be used to measure the bilayer thickness of lipid vesicles and biological membranes with sub-angstrom precision (Heberle et al. 2020 PNAS 117:19943). Despite the great potential of cryo-EM for bilayer structural studies, factors that influence the primary data have not been systematically evaluated. Here, we investigate the influence of energy filtering, contrast transfer function corrections, and instrument defocus length on the primary image data. We report on how these parameters influence such measurements as distributions of membrane thickness, average radial intensity profiles across the bilayer, and spatial autocorrelation of the bilayer thickness. Experimental measurements were correlated with images calculated from two-dimensional projections of atomistic molecular simulations of lipid bilayers, convolved with a contrast transfer function to mimic primary cyro-EM data. This approach yields insights into the molecular origins of measurements quantified from images. We also explored the influence of membrane curvature on thickness using DOPC vesicles of varying diameter prepared via sonication or extrusion through pore sizes ranging from 30-200 nm in diameter. The smallest vesicles exhibited bilayer thinning consistent with curvature stress. The practical implications of instrument settings on the analysis of single and multicomponent lipid membranes and how membrane curvature differs depending on observed size are discussed. These efforts demonstrate how data collection can be systematically optimized to maximize the potential of cryo-EM for resolving variation in membrane thickness within biological membranes.

Schneiderian membrane thickness variation following endodontic procedures: a retrospective cone beam computed tomography study

BackgroundTo assess the change of the Schneider membrane thickness measured by CBCT before and after root canal treatment, retreatment and pulp capping procedures.MethodsThis retrospective study was conducted on CBCT scans of a patient population of Guy’s Hospital NHS Foundation Trust, London. Three groups of patients were studied: Group 1 consisted of patients referred for primary endodontic treatment; Group 2 for endodontic retreatment; Group 3 for indirect pulp capping procedures (serving as a control group). Follow up scans were carried out 1 year after treatment. Measurements were carried out on CBCT scans and data were analysed statistically by Wilcoxon Signed Rank Test. Linear regression was used to assess predictive parameters for membrane thickness.ResultsA statistically significant reduction of the Schneider membrane thickness was observed one year after endodontic treatment and retreatment (P < 0.05) but no significant reduction was observed after pulp capping procedures. Linear regression showed that age and gender were significant predictors influencing the Schneider membrane thickness.ConclusionsWithin the limitations of this retrospective study, following root canal treatment and re-treatment a Schneiderian membrane thickness reduction occurred at 1-year follow-up.The removal of odontogenic infection following endodontic treatment may help reducing the thickness of the Schneider membrane.

Fringing Capacitive Effect of Silicon Carbide Based Nano-Electro-Mechanical-System Micromachined Ultrasonic Transducers: Analytical Modeling and FEM Simulation

This paper models the fringing field effects in a capacitive micromachined ultrasonic transducer (CMUT) structure for determining the sensitivity of the device. CMUT is used as a medical imaging component which can be an important module for sustainable healthcare system. The capacitance value of the device is evaluated based on Younes Ataiiyan’s method. To determine the equivalent capacitance of the device, the capacitances of the membrane, gap and silicon nitride insulating layer are associated in series. Mason’s modeling techniques are used to evaluate the membrane displacement. Circular membrane approximation model has been considered. Effects of the variation in membrane thickness, gap separation, and membrane radius on membrane displacement are investigated. The analytical prediction has been validated with the finite element method simulation results through PZFlex. Three dimensional modeling is carried out to accurately capture the characteristic behavior of the device. The agreements of both results are excellent which verifies that fringing field effects exist in the device operation.

Single-cell unroofing: probing topology and nanomechanics of native membranes

Cell membranes separate the cell interior from the external environment. They are constituted by a variety of lipids; their composition determines the dynamics of membrane proteins and affects the ability of the cells to adapt. Even though the study of model membranes allows to understand the interactions among lipids and the overall mechanics, little is known about these properties in native membranes. To combine topology and nanomechanics analysis of native membranes, I designed a method to investigate the plasma membranes isolated from a variety of single cells. Five cell types were chosen and tested, revealing 20% variation in membrane thickness. I probed the resistance of the isolated membranes to indent, finding their line tension and spreading pressure. These results show that membranes isolated from neurons are stiffer and less diffusive than brain cancer cell membranes. This method gives direct quantitative insights on the mechanics of native cell membranes.

Molecular dynamics simulation and experimental investigation of furfural separation from aqueous solutions via PEBA-2533 membranes

Abstract Molecular dynamics (MD) simulation was adopted to study the feed-membrane surface affinity and transport behavior of furfural molecules when a poly(ether block amide) (PEBA-2533) membrane was employed. The furfural molecules exhibited a stronger interaction with the PEBA-2533 membrane than the water molecules. Transport behavior analysis indicated that the self-diffusion selectivity in the membrane increased with an increase in feed furfural concentration and the cavity size of the membrane was crucial for the separation of larger molecules. Additionally, the fractional free volume, fractional accessible volume, and fractional cavity volume (FCV) of the PEBA-2533 membrane were analyzed to reveal the variation in membrane structure. Interestingly, the water flux was more sensitive to the variation in membrane thickness than the furfural flux. The permeate furfural concentration increased with an increase in membrane thickness and a membrane selectivity damping model was proposed to explain this phenomenon. The MD technique showed great potential as an approach to characterize the performance of the PEBA-2533 membrane during the pervaporation process.

Modelling and prediction of organic solvent flux and retention of surfactants by organic solvent nanofiltration

A model that predicts the individual and mixed fluxes of pure solvent and surfactant through PDMS organic solvent nanofiltration membranes as well as the retention of the non-ionic surfactant Marlipal 24/70 from 1-dodecene was developed based on the solution diffusion model. In contrast to available models it requires only one fitting parameter that is independent of operating conditions. The other model parameters were estimated from detailed experimental observations independent from filtration data or literature values. Dependencies of the diffusion coefficients and molar volume on temperature and pressure, as well as membrane swelling and compaction were considered. Using the model fitted to filtration data at one operating condition it was possible to predict pure solvent flux with high accuracy for four different PDMS based membranes in a temperature range of 10–45°C at pressures of 15–35bar. Phenomenological behaviour of mixed solvent and surfactant flux were described accurately in every case. For temperature and membrane thickness variations, the model predicted solvent and surfactant flux within experimental uncertainty. Retentions, however, were accurately described.

A Silicon-Based Porous Thin Membrane as a Cancer Cell Transmigration Assay

This paper presents a novel microfabricated Boyden chamber in silicon with well-defined pore sizes and controlled membrane thickness for cell migration analysis. The chip-based chamber is fabricated employing lithography and deep reactive ion etching techniques on a double-sided polished silicon wafer. The device contains micro-pores with a silicon oxide layer at the top and a deep microfluidic channel at the bottom, which is anodically-bonded to a glass wafer for sealing and facilitating the imaging and chemoattractant feeding. The applicability of the chip has been demonstrated through the distinct migratory behaviors of highly metastatic breast cancer cells, MDA-MB-231, through pores with 8 $\mu \text{m}$ in diameter, 50 $\mu \text{m}$ in spacing, and 30 $\mu \text{m}$ in thickness. Employing the above technique, the membrane thickness variation among different chips was below 10%. Utilizing this micro-Boyden chamber device, we have shown that MDA-MB-231 cells migrated distinctively in higher rate than the cells which had gone through sphingosine kinase inhibitor drug treatment or no chemoattractant feeding over a course of 12 hours. Furthermore, we validated the performance of the micro-Boyden chamber by quantifying the migration rate of the cancer cells under different chemoattractant gradient profiles. [2016-0103]

4-5.電解質膜厚の違いによる固体高分子形燃料電池の発電特性と膜内水分濃度分布((2)分散型エネルギーシステムII,Session 4 分散型エネルギーシステム)

4-5.電解質膜厚の違いによる固体高分子形燃料電池の発電特性と膜内水分濃度分布((2)分散型エネルギーシステムII,Session 4 分散型エネルギーシステム)

The Single Transmembrane Segment of Minimal Sensor DesK Senses Temperature via a Membrane-Thickness Caliper.

The ability to sense and respond to extracellular signals is essential for cell survival. One example is the cellular response to temperature variation. How do cells "sense" temperature changes? It has been proposed that the bacterial thermosensor DesK acts as a molecular caliper measuring membrane thickness variations that would occur as a consequence of temperature changes and activates a pathway to restore membrane fluidity at low temperature. Here, we demonstrated that membrane thickness variations do occur at physiological temperatures by directly measuring Bacillus lipid membrane thickness. We also dissected the N-terminal sensing motif of MS-DesK at the molecular-biophysical level and found that the dyad phenylalanine-lysine at the water-lipid phase is critical for achievement of a fine-tuned sensitivity to temperature.

A model for a crack or a delaminated region in a PEM fuel cell anode: analytical solutions

We develop a model for the potential and current density distributions in and around a long, straight and inactive (“dead”) gap inside a PEM fuel cell anode. Physically speaking, such gaps represent cracked or delaminated domains in an anode catalyst layer. The dead region is modeled as a step function for the anode exchange current density. An analytical solution to the model equations is derived; the solution exhibits a large peak of the anode current density japeak just outside the gap. For a typical cell current density of 1Acm−2, a gap with a width of 400μm induces japeak of about 4Acm−2. For smaller gap widths on the order of 10μm, which is typical for cracks, the effect is marginal. Variations in membrane thickness have a minor effect on japeak.

Vibrational modes of ultrathin carbon nanomembrane mechanical resonators

We report measurements of vibrational mode shapes of mechanical resonators made from ultrathin carbon nanomembranes (CNMs) with a thickness of approximately 1 nm. CNMs are prepared from electron irradiation induced cross-linking of aromatic self-assembled monolayers and the variation of membrane thickness and/or density can be achieved by varying the precursor molecule. Single- and triple-layer freestanding CNMs were made by transferring them onto Si substrates with square/rectangular orifices. The vibration of the membrane was actuated by applying a sinusoidal voltage to a piezoelectric disk on which the sample was glued. The vibrational mode shapes were visualized with an imaging Mirau interferometer using a stroboscopic light source. Several mode shapes of a square membrane can be readily identified and their dynamic behavior can be well described by linear response theory of a membrane with negligible bending rigidity. By applying Fourier transformations to the time-dependent surface profiles, the dispersion relation of the transverse membrane waves can be obtained and its linear behavior verifies the membrane model. By comparing the dispersion relation to an analytical model, the static stress of the membranes was determined and found to be caused by the fabrication process.

Characterisation of a polyaromatic PBI blend membrane for SO2 electrolysis

The application of a polyaromatic acid–base blend membrane from partially fluorinated and sulfonated aromatic polyether and the polybenzimidazole F6PBI has been investigated for hydrogen production using SO2 electrolysis. Several membrane electrode assembly (MEA) pre-doping strategies have been investigated using polarisation curves. Membrane thickness variation, voltage cycling and long term operation at constant current (0.1 A cm−2) was also performed. Scanning electron microscopy (SEM) and TGA-MS was used to evaluate MEA stability before and after long term operation. It was found that doping the MEA after hot pressing performs the best reaching a current density of 0.3 A cm−2. The performance could also be improved by cycling the voltage 16 times to reach 0.33 A cm−2. Long term operation showed stable voltage at 0.1 A cm−2 staying below 0.8 V. SEM images showed that no significant sulfur deposition was present while TGA-MA analysis confirmed some degradation after the 140 h of operation.

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H2SO4 as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H2SO4 concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D(o) was calculated as 1.36 × 10−7 cm2 s−1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.

Aquivion® PerfluoroSulfonic Acid ionomer membranes: A micro-Raman spectroscopic study of ageing

Recent interest in alternative energy technologies promoted the development of perfluorinated polymer membranes for fuel cells; the degradation mechanism occurring during operation and the polymer ageing that may lead to membrane failure are still a matter of investigation with the aim to identify proper testing protocols and analytical methods. This study illustrates some results obtained through micro Raman spectroscopy; this analytical technique showed itself to be a powerful tool in terms of spatial resolution and chemical data gathering. Detailed analytical and structural information along the cross sections of two membrane grades have been presented, shedding light on intrinsic structural modifications related to overall membrane performance. This study clearly shows an ununiformly distributed loss of sulfonic groups in two different Aquivion® membrane grades, being the spectroscopic technique able to unveil very subtle effects due to equivalent weight and membrane thickness variations. The overall results support the mechanism previously proposed by other authors using different analytical techniques.

Bilayer Elasticity at the Nanoscale: The Need for New Terms

Continuum elastic models that account for membrane thickness variations are especially useful in the description of nanoscale deformations due to the presence of membrane proteins with hydrophobic mismatch. We show that terms involving the gradient and the Laplacian of the area per lipid are significant and must be retained in the effective Hamiltonian of the membrane. We reanalyze recent numerical data, as well as experimental data on gramicidin channels, in light of our model. This analysis yields consistent results for the term stemming from the gradient of the area per molecule. The order of magnitude we find for the associated amplitude, namely 13–60 mN/m, is in good agreement with the 25 mN/m contribution of the interfacial tension between water and the hydrophobic part of the membrane. The presence of this term explains a systematic variation in previously published numerical data.