Water Transport Mechanisms Research Articles

Synthesis of dual pH‐ and temperature‐sensitive poly(N‐isopropylacrylamide‐co‐acrylic acid)/sewage sludge ash hydrogel with the simultaneously high performance of swelling and deswelling

AbstractAn advanced dual pH‐ and temperature‐sensitive hydrogel (NASH2.5) was optimally synthesized through modification of N‐isopropylacrylamide (NIPAM) hydrogel with introducing 5 mol% acrylic acid (AA) and 2.5 wt% sewage sludge ash (SSA). The swelling kinetic results showed that NASH2.5 exhibited both high equilibrium swelling ratio and swelling rate, which was attributed to the higher porous structure as shown in scanning electron microscope, and the more hydrogen bonding formed inside of the hydrogel as investigated in Fourier transform infrared spectrometer. In addition, its curve was better fitted to the pseudo‐second‐order model, indicating that the water absorption process was dominated by chemisorption through forming the hydrogen bonding among the water molecules and carboxyl/silanol groups of the hydrogel. Compared with the pure NIPAM hydrogel, the water transport mechanism switched from Case I diffusion to Case II diffusion by introduction of AA and further SSA. Furthermore, through the results of the deswelling kinetics in pH value change (from 9 to 4 and 2, respectively), temperature value change (from 25 to 40, 50, and 60°C, respectively), and dual pH and temperature values changes, NASH2.5 not only presented a high pH sensitivity, but also showed high sensitive to temperature by achieving high water recovery ratio in rapid dehydrated rate. Therefore, the dual stimuli‐sensitive hydrogel with the simultaneously high performance of swelling and deswelling would provide a suitable alternative for specific applications such as pollutant adsorption.

True driving force and characteristics of water transport in osmotic membranes

Diffusion cannot be a major water transport mechanism in osmotic membranes because of the lack of true water concentration gradient within the membrane. Due to the semipermeable property of osmotic membranes, water concentration in the membrane is virtually constant because of the absence of salts. The recently confirmed porous structure of the skin layer of osmotic membranes cannot support the basis to exclude bulk water flow in the membrane as assumed in the classic solution-diffusion model. Herein we demonstrate that the concentration difference of water at the membrane-solution interface manifests itself as a negative hydraulic pressure in the membrane. Hence, the only possible driving force for water movement in osmotic membranes is hydraulic pressure gradient. Osmotically driven membrane processes are characterized with negative pressure within the membrane below the water vapor pressure, inevitably leading to the formation of vapor or small bubbles within the membrane matrix. This phenomenon is expected to markedly reduce the effectiveness of osmotic pressure as a driving force for water transport. Delineation of the breakdown and possible restoration of water continuity under negative pressure is essential for proper understanding of the principles governing water transport in osmotic membranes.

Water flooding behavior in flow cells for ammonia production via electrocatalytic nitrogen reduction

The green production of ammonia, in an electrochemical flow cell under ambient conditions, is a promising way to replace the energy-intensive Haber-Bosch process. In the operation of this flow cell with an alkaline electrolyte, water is produced at the anode but also required as an essential reactant at the cathode for nitrogen reduction. Hence, water from the anode is expected to diffuse through the membrane to the cathode to compensate for the water needed for nitrogen reduction. Excessive water permeation, however, tends to increase the possibility of water flooding, which would not only create a large barrier for nitrogen delivery and availability, but also lead to severe hydrogen evolution as side reaction, and thus significantly lower the ammonia production rate and Faradaic efficiency. In this work, the water flooding phenomenon in flow cells for ammonia production via electrocatalytic nitrogen reduction is verified via the visualization approach and the electrochemical cell performance. In addition, the effects of the nitrogen flow rate, applied current density, and membrane thickness on the water crossover flux and ammonia production rate are comprehensively studied. The underlying mechanism of water transport through the membrane, including diffusion and electro-osmotic drag, is precisely examined and specified to provide more insight on water flooding behavior in the flow cell.

The mechanisms of water transport in the capillary fringe: sandbox experiments and numerical studies

The mechanisms of water transport in the capillary fringe: sandbox experiments and numerical studies

Water Absorption Kinetics in Composites Degraded by the Radiation Technique.

Rubber-based wastes represent challenges facing the global community. Human health protection and preservation of environmental quality are strong reasons to find more efficient methods to induce degradation of latex/rubber products in order to replace devulcanization, incineration, or simply storage, and electron beam irradiation is a promising method that can be can be taken into account. Polymeric composites based on natural rubber and plasticized starch in amounts of 10 to 50 phr, obtained by benzoyl peroxide cross-linking, were subjected to 5.5 MeV electron beam irradiation in order to induce degradation, in the dose range of 150 to 450 kGy. A qualitative study was conducted on the kinetics of water absorption in these composites in order to appreciate their degradation degree. The percentages of equilibrium sorption and mass loss after equilibrium sorption were found to be dependent on irradiation dose and amount of plasticized starch. The mechanism of water transport in composites was studied not only through the specific absorption and diffusion parameters but also by the evaluation of the diffusion, intrinsic diffusion, permeation, and absorption coefficients.

Molecular dynamics study of water transport through AQP5-R188C mutant causing palmoplantar keratoderma (PPK) using the gating mechanism concept

It is widely known that any disruption to the water regulation in aquaporins (AQPs) leads to numerous important diseases. However, studies of dynamics and energetics of disease-causing mutations in the aquaporins on the molecular level are still limited. In the present work, the effects of a skin disease-causing mutant, R188C, on the structure of AQP5 and water transport mechanism within this mutated aquaporin are investigated using the concept of gating mechanism. Our results have revealed that the R188C mutation causes a remarkable increase in the pore radius inside the selectivity filter (SF) region facilitating the passage of water molecules. This observation is supported by plotting the free energy profiles of water molecules transport and calculating permeability values through AQP5-R188C, such that the energy barrier in the SF region of the pores was substantially reduced by this mutation, and therefore, the translocation of water molecules was improved. The total averaged osmotic permeability for R188C has been computed as about 11-fold of the wild-type permeability. However, a comparison between the osmotic permeability values related to the open conformation of CE revealed that this coefficient for AQP5-R188C is about 6.5 times larger than that of wt-AQP5, which can be a more accurate value according to the gating mechanism associated with the constriction region of the aquaporin.

The transcriptome of anal papillae of Aedes aegypti reveals their importance in xenobiotic detoxification and adds significant knowledge on ion, water and ammonia transport mechanisms

The anal papillae of mosquito larvae are osmoregulatory organs in direct contact with the external aquatic environment that actively sequester ions and take up water in dilute freshwater. In the disease vector Aedes aegypti mechanisms of ion, water and ammonia transport have only been partially resolved. Furthermore, A. aegypti larvae are known to reside in high ammonia sewage and high salt brackish waters, and understanding of anal papillae function in these conditions is in its infancy. The objective of this study was to identify the complement of ion and water transport genes expressed by the anal papillae of freshwater larvae by sequencing their transcriptome, and comparing their expression in anal papillae of larvae abruptly transferred to brackish water for 24 h. Results identified a number of ion and water transport proteins, ammonia detoxifying enzymes, a full suite of xenobiotic detoxifying enzymes and transporters, and G-protein coupled receptors of specific hormones. We identified a marked increase in transcript and protein abundance of aquaporin AaAQP2 in the anal papillae with abrupt transfer to brackish water. We present an updated and more comprehensive model for ion and water transport with additional putative transporters for Na+ and Cl- uptake in the anal papillae. These are organs which are actively engaged in Na+, Cl- and water uptake and regulation when the aquatic larvae encounter fluctuating salinities over the course of their development. Furthermore the transcriptome of the anal papillae includes a full set of xenobiotic detoxification genes suggesting that these are important detoxification organs which is particularly important when larvae reside in polluted water.

From Pinocytosis to Methuosis-Fluid Consumption as a Risk Factor for Cell Death.

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell’s surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and—most importantly—shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement.

Microarchitecture of polyvinylidene fluoride-bound self-standing microporous layer and its implication to water management in fuel cells

This study presents novel self-standing microporous layers (SSMPLs) for proton exchange membrane fuel cells (PEMFCs). SSMPLs with polyvinylidene fluoride (PVDF) as a binder were readily fabricated using the facile tape-casing and peeling-off method proposed in this study. The surface morphology, pore size distribution, and wettability of the SSMPLs with different carbon loadings and PVDF contents were investigated and compared with those of a commercially available polytetrafluoroethylene (PTFE)-bound gas diffusion layer. Experimental and theoretical studies using electrochemical impedance spectroscopy and the limiting current method were performed to elucidate the mechanism by which PVDF-bound SSMPL leads to higher PEMFC performance. The individual microstructures of PVDF-bound SSMPL and PTFE-bound MPL were visualized by using atomic force microscopy to distinguish the binder and carbon agglomerates and the water transport mechanism through each MPL was suggested.

Osmoregulation in fish sperm.

In most fish exhibiting external fertilization, spermatozoa become motile after release into water, triggered by differences between intracellular and extracellular conditions such as osmotic pressure, ion composition, and pH. The rapid change in osmolarity initiating spermatozoon motility induces osmotic pressure, resulting in active water movement across the cell membrane. Mechanisms of ion and water transport across the plasma membrane and cell volume regulation are important in maintaining structure and functional integrity of the cell. The capacity of the fish spermatozoon plasma membrane to adapt to dramatic environmental changes is an essential prerequisite for motility and successful fertilization. Adaptation to change in external osmolality may be the basis of spermatozoon function and an indicator of sperm quality. The involvement of specific water channels (aquaporins) in cell volume regulation and motility is highly likely. The goal of this review is to describe basic mechanisms of water transport and their role in fish spermatozoon physiology, focusing on osmoresistance, cell volume regulation, motility, and survival.

Soil Erosion and Controls in the Slope-Gully System of the Loess Plateau of China: A Review

The Loess Plateau has long been suffering from serious soil erosion of which erosion from the slope-gully system is now dominant. The slope-gully system is characterized with distinctive erosion distribution zones consisting of inner and inter gully areas wherein erosion patterns spatially vary, acting as both sediment source and the dominant sediment and water transport mechanism. In this paper, a substantial body of research is reviewed concentrating on the soil erosion processes and control practices in the slope-gully system. The inner gully area is identified as the main sediment source while runoff and sediment from the inter-gully upland is found to significantly affect down slope erosion processes. Correspondingly, the protective vegetation pattern and coverage should be strategically designed for different erosion zones with an emphasis on the critical vegetation cover and pattern to reduce sediment yield of the whole slope-gully system. Check-dam could change the base level of erosion and reduce the slope length of the gully side, which will further decrease the possibility and magnitude of gravity erosion. We concluded that understanding the erosion processes and implementing erosion practices for the slope-gully system are of importance and require more research efforts that emphasize: 1) the influence of upland runoff on erosion processes at downslope; 2) the relationship between hydraulic characteristics of overland flow and erosion process at a slope-gully system scale; 3) physical mechanisms of different vegetation patterns on the slope-gully erosion process.

Transcriptome of Cenostigma pyramidale roots, a woody legume, under different salt stress times.

Salinity stress has a significant impact on the gain of plant biomass. Our study provides the first root transcriptome of Cenostigma pyramidale, a tolerant woody legume from a tropical dry forest, under three different salt stress times (30 min, 2 h, and 11 days). The transcriptome was assembled using the RNA sequencing (RNA-Seq) de novo pipeline from GenPipes. We observed 932, 804, and 3157 upregulated differentially expressed genes (DEGs) and 164, 273, and 1332 downregulated DEGs for salt over 30 min, 2 h, and 11 days, respectively. For DEGs annotated with the Viridiplantae clade in the early stress periods, the response to salt stress was mainly achieved by stabilizing homeostasis of such ions like Na+ and K+ , signaling by Ca2+ , transcription factor modulation, water transport, and oxidative stress. For salt stress at 11 days, we observed a higher modulation of transcription factors including the WRKY, MYB, bHLH, NAC, HSF, and AP2-EREBP families, as well as DEGs involved in hormonal responses, water transport, sugar metabolism, proline, and reactive oxygen scavenging mechanisms. Five selected DEGs (K+ transporter, aquaporin, glutathione S-transferase, cyclic nucleotide-gated channel, and superoxide dismutase) were validated by qPCR. Our results indicated that C. pyramidale had an early perception of salt stress modulating ionic channels and transporters, and as the stress progressed, the focus turned to the antioxidant system, aquaporins, and complex hormone responses. The results of this first root transcriptome provide clues on how this native species modulate gene expression to achieve salt stress tolerance.

Molecular dynamics simulations reveal statistics and microscopic mechanisms of water permeation in membrane-embedded artificial water channel nanoconstructs.

Understanding water transport mechanisms at the nanoscale level remains a challenge for theoretical chemical physics. Major advances in chemical synthesis have allowed us to discover new artificial water channels, rivaling with or even surpassing water conductance and selectivity of natural protein channels. In order to interpret experimental features and understand microscopic determinants for performance improvements, numerical approaches based on all-atom molecular dynamics simulations and enhanced sampling methods have been proposed. In this study, we quantify the influence of microscopic observables, such as channel radius and hydrogen bond connectivity, and of meso-scale features, such as the size of self-assembly blocks, on the permeation rate of a self-assembled nanocrystal-like artificial water channel. Although the absolute permeation rate extrapolated from these simulations is overestimated by one order of magnitude compared to the experimental measurement, the detailed analysis of several observed conductive patterns in large assemblies opens new pathways to scalable membranes with enhanced water conductance for the future design.

Observation and Analysis of Water and Salt Transports in the North Branch of the Changjiang Estuary

Gu, J.; Zhu, J., and Lyu, H., 2021. Observation and analysis of water and salt transports in the North Branch of the Changjiang Estuary. Journal of Coastal Research, 37(3), 518–527. Coconut Creek (Florida), ISSN 0749-0208.The North Branch (NB) is the first-order bifurcation of the Changjiang Estuary and is an extremely shallow water channel. The greatest characteristic of saltwater intrusion is the saltwater spillover from the NB into the South Branch (SB). A field observation was conducted in the NB from 21 to 27 February 2017 to understand the water current and salinity variation. The residual unit width water and salt fluxes, as well as their decomposed terms, were calculated to discuss the mechanisms of water and salt transport. The tidal and vertical variations in ebb and flood duration, current velocity, and salinity during the neap-middle-spring tide were presented and dynamically analyzed in detail. The direction of the Eulerian water and salt transports and tidal pumping salt transport varied by site, vertical layer, and tidal type, whereas the Stokes drift water and salt transports were landward. During neap tide, the total residual water and salt fluxes in the upper layer of the whole NB were seaward transported because of the runoff effect; the total water and salt fluxes in the lower layer were landward in the lower-middle and lower reaches of the NB, reflecting the existence of a two-layer estuarine circulation. During the moderate tide, the total residual water and salt fluxes were seaward in the whole NB except in the lower layer in the low reaches of the NB, which were landward due to the strong baroclinic effect. During the spring tide, all the total residual water and salt fluxes were landward because some flood water flowed into the SB, resulting in an imbalance between the flood and ebb water volumes in the NB. The dynamic processes of water and salt transport from the NB into the SB during spring tide were revealed by the observation and flux decomposition method.

Study on the mechanism of water transport near the surface of pristine and nitrogen-doped β-graphyne

The transport mechanism of water molecules on the surface of single-layer [Formula: see text]-graphyne is investigated from the first-principles calculations. The result indicates that when water molecules are adsorbed in different stances, their corresponding transport paths are different. When N atoms are doped with sp carbon atoms, the transport pathway of water molecules is opposite to that of intrinsic [Formula: see text]-graphyne, which is due to the charge transfer between atom s. Consequently, this study is conducive to understand the mechanism of nanoscale water transport on the graphyne surface and provides a theoretical basis for exploring the interaction between water and graphyne.

Molecular dynamics study on water and ions transport mechanism in nanometer channel of 13X zeolite

Understanding the atomistic transport within nanoporous zeolite is essential in a broad field. Herein, molecular dynamics was systematically utilized to elucidate the migration mechanism of pure water and NaCl solution in the 13X zeolite. At nano-scale level, molecular simulation clearly distinguishes the wetting and saturating stages of water transport in porous zeolite. The interior skeleton of 13X zeolite provides plenty of oxygen sites with strong polarity, which attracts frontier water molecules to infiltrate the hydrophilic zeolite surface rapidly in nearly 2 ns. The ladder-like ingress curve for water molecules highlight the discontinuous remain-jump wetting process that is induced by the competition adsorption with oxygen sites between the subsequent water molecules and the front water molecules. Initial wetting on interior surface reduces significantly the permeability of subsequent water transport. Furthermore, the penetrated water molecules, competing oxygen sites with extra-framework cations, can cause cations to exhibit different hydration behavior. Additionally, the permeability of water flux throughout zeolite channel is reduced by 10% as the Na+ and Cl- are incorporated in solution. Na+ with large hydration shells are sieved by bottlenecks formed by the windows of 12-ring structure with a diameter of 7.38 Å. The accumulated Na+ at the entrance region associate with neighboring water molecules and hydroxyl oxygen atoms to form hydrated clusters and ionic pairs, which plays as a physical barrier in blocking water transport. Decoding of the transport mechanism of water and salt solutions in zeolites at the molecular level facilitates breaking the existing upper limit of energy storage density and water treatment efficiency.

Swellable catheters based on a dynamic expanding inner diameter

Intravenous (IV) fluid administration is critical for all patients undergoing care in a hospital setting. In-patient hospital practice, surgeries, and emergency care require functional IVs for fluid replacement and medication administration. Proper placement of IVs is vital to providing medical services. The ease of placement of an IV catheter, however, depends not only on the size of the catheter but also on provider experience and patient demographics such as age, body mass index, hydration status, and medical comorbidities present challenges to successful IV placement. Smaller diameter IV placement can improve success and there are instances where multiple small diameter catheters are placed for patient care when larger bore access is unattainable. Smaller inner-diameter catheters for anesthesia have functional constraints. Ideally, there would be a smaller catheter for placement that could function as a larger catheter for patient care. One solution is the idea of functionally responsive catheters. Here, we evaluated tubular-shaped hydrogels as potential functional catheters that can increase in inner diameter through fluid swelling using cross-linked homopolymers of polyacrylamide, PAM (10–40% w/w), and their copolymers with 0–8% w/w Poly-(Ethylene Glycol)-Diacrylate, PEGDA. For the PAM gels, the water transport mechanism was shown to be concentration-dependent Fickian diffusion, with the less concentrated gels exhibiting increasingly anomalous modes. Increasing the PEGDA content in the network yielded an initial high rate of water uptake, characterized by Case II transport. The swelling kinetics depended strongly on the sample geometry and boundary conditions. Initially, in a submerged swelling, the annulus expands symmetrically in both outward and inward directions (it thickens), reducing the internal diameter by up to 70%. After 1 h, however, the inner diameter increases steadily so that at equilibrium, there is a net (>100%) increase in all the dimensions of the tube. The amount of linear swelling at equilibrium depended only on the polymer volume fraction as made, while the rate of inner diameter expansion depended on the hydrophilicity of the matrix and the kinetics of sorption. This study serves as proof of concept to identify key parameters for the successful design of hydrogel-based catheter devices with expanding inner-diameters for applications in medical care.

Molecular mechanisms of brain water transport.

Our brains consist of 80% water, which is continuously shifted between different compartments and cell types during physiological and pathophysiological processes. Disturbances in brain water homeostasis occur with pathologies such as brain oedema and hydrocephalus, in which fluid accumulation leads to elevated intracranial pressure. Targeted pharmacological treatments do not exist for these conditions owing to our incomplete understanding of the molecular mechanisms governing brain water transport. Historically, the transmembrane movement of brain water was assumed to occur as passive movement of water along the osmotic gradient, greatly accelerated by water channels termed aquaporins. Although aquaporins govern the majority of fluid handling in the kidney, they do not suffice to explain the overall brain water movement: either they are not present in the membranes across which water flows or they appear not to be required for the observed flow of water. Notably, brain fluid can be secreted against an osmotic gradient, suggesting that conventional osmotic water flow may not describe all transmembrane fluid transport in the brain. The cotransport of water is an unconventional molecular mechanism that is introduced in this Review as a missing link to bridge the gap in our understanding of cellular and barrier brain water transport.

Ion-exchange mechanisms and interfacial reaction kinetics during aqueous corrosion of sodium silicate glasses

The ion-exchange and associated interfacial reaction mechanisms of silicate glasses are critical in elucidating their aqueous corrosion behaviors, surface modification and property changes, hence have potential impact on both science and technology. This work reports findings of the atomic and nanoscale details of the glass–water interfacial reactions revealed by applying reactive force field (ReaxFF) based molecular dynamics (MD) simulations, from which the key mechanisms of the ion exchange, as well as the kinetics of associated interfacial reactions, are elucidated. It was found that the Na+ and H+ ion exchange can happen between two oxygen ions on a single silicon oxygen tetrahedron or adjacent tetrahedra. In addition, the clustered reaction of two non-bridging oxygens mediated by an adjacent water molecule was also identified. The latter reaction might be the main mechanism of water transport after initial surface reactions that consume the non-bridging oxygen species on the surface. Water molecules thus can play two roles: as an intermediate during the proton transfer processes and as a terminator of the clustered reactions. Statistical analyses were performed to obtain reaction kinetics and the results show that silanol formation is a more favored process than the silanol re-formation within the first 3 ns of interfacial reactions. The results obtained thus shed lights on the complex ion-exchange mechanisms during glass hydration and enable more detailed understanding of the corrosion and glass–water interactions of silicate glasses.

An intelligent parametric modeling and identification of a 5 kW ballard PEM fuel cell system based on dynamic recurrent networks with delayed context units

This article presents a dynamic simulation study for the modeling and identification of a 5 kW Proton Exchange Membrane (PEM) fuel cell system using intelligent ANN approach to get rid of the complexity involved in the analytical modeling as it is intricate with the highly non-linear dynamics such as electrochemical, thermodynamic and water-transport mechanisms. The proposed artificial networks for the prediction and identification of a highly non-linear fuel cell system performance are Radial Basis Function Network (RBFN), dynamic Elman Recurrent Network (ERN) and NARX Recurrent Network (NRN) that has delayed context unit. A comparative study is made between the performances of the proposed neural network models for identifying an optimal network structure and configuration based on network performance measures. The optimal NARX network ascertained having an appreciable learning and generalization ability is adopted for the prediction and identification of the fuel cell system for its static and dynamic behavior. The network prediction over the system behavior shows good agreement with the benchmark results acquired from a 5 kW-Ballard fuel cell system. The proposed optimal intelligent parametric model can facilitate in replacing a highly non-linear fuel cell system in the fuel cell related model developments that are adopted in several research sectors particularly in transportation applications.