Water Transport Kinetics Research Articles

Limiting Current Density in Water Vapor-Fed Polymer Electrolyte Membrane Electrolyzers

Polymer electrolyte membrane water electrolyzers (PEMWE) are a critical technology in development for addressing the need for efficient hydrogen production. In order to make hydrogen a cost-effective fuel or industrial feedstock, the overpotentials across the cell needs to be decreased and platinum-group metal loading reduced. Devising novel electrode structures that enable ultra-high current densities at low oxygen evolution reaction (OER) catalyst (e.g. Iridium oxide) loadings is one approach to achieving efficiency and cost targets. One of the overpotentials that needs to be addressed is due to mass transport limitations within the porous transport layer (PTL) and anode catalyst layer, which could be a limiting factor at ultra-high current densities. When operating at ultra-high current densities, the rate of the OER may reach a point at which oxygen gas bubbles fill the pores of the anode catalyst layer PTL, blocking access of liquid water to the anode catalyst layer. Because of this, there is a possibility that the cell will rely on water vapor diffusion through the evolving oxygen gas to deliver the water reactant to the OER catalyst. To assess the limitation of a PEMWE while relying on water vapor diffusion, a commercially manufactured membrane electrode assembly (MEA) was tested by flowing water vapor into the anode as the reactant. With the aim of identifying a limiting current density (LCD) of the electrolyzer under these conditions, potentiostatic polarization curves were obtained for a range of relative humidities (RH) and back pressures. The RH was varied to assess the impact of reactant concentration on the LCD, while the back pressure was varied to identify the impact of the molecular gas diffusion coefficient on the LCD. In this presentation, we will present our analysis of the significance of the water vapor diffusion transport resistance through the pressure-dependent resistance evaluation. Furthermore, we will discuss application of this approach to evaluating the impact of vapor operation on membrane water transport and OER reaction kinetics.

Kinetic description of water transport during spontaneous emulsification induced by Span 80.

Spontaneous emulsification is a phenomenon that forms nanometer-sized droplets (nanodroplets) without the application of any external force, and the mechanism has been actively studied for application to various technologies. In this study, we analyzed the kinetics of spontaneous emulsification induced by Span 80. The measurement of water concentration in Span 80 hexadecane solution indicated that the chemical potential of water in the nanodroplets decreased as the amount of water in the nanodroplets decreased. Based on this result, water transport between the aqueous phase and nanodroplets in which the chemical potential of water was controlled was quantitatively investigated by using a microfluidic device. The results demonstrate that the kinetics of water transport during spontaneous emulsification induced by Span 80 was described by a model of osmotic transport through an organic liquid film between the aqueous phase and nanodroplets.

Water diffusion mechanisms in bitumen studied through molecular dynamics simulations

Water transport is one of the major factors responsible for moisture damage in asphalt pavements. To study the thermodynamics and kinetics of water transport in bitumen and to uncover microscale mechanisms of moisture-induced damage, molecular dynamics simulations were performed for up to 600 ns for water–bitumen systems with realistic water contents that varied from 0 to 1.76 wt%. Hydrogen bonding interactions and clustering of water molecules at various combinations of temperature and water content were investigated, and their effects on the self-diffusion coefficient of water and bitumen properties are computed and discussed. It is shown that the saturated water concentration in bitumen is small, especially at low temperatures, and additional water molecules tend to form large water clusters via hydrogen bonding, indicating micro-phase separation of the water and bitumen phases inside the simulation box. Hydrogen bonding and water clustering play a crucial role on the magnitude of the self-diffusion coefficient of water. Physical properties of bitumen that include viscosity and cohesive energy are affected by water. The presence of large water clusters is indicative of how degradation in cohesion is observed on the microscale.

Use of brick dust to optimise the dewatering process of hydrated lime mortars for conservation applications

The impact of dewatering on lime mortars modified using brick dust was studied, as it is of particular importance in conservation applications. Dewatering takes place when freshly mixed mortars come into contact with a porous substrate, such as brick or stone, during on site construction. Since the dewatering process between the mortar and its substrate can modify the mortar properties, understanding the dewatering process enables pozzolan-modified hydrated lime mortars to be optimised for the masonry units being bonded. Evaluation of the water transport kinetics on brick dust—hydrated lime binder systems demonstrated their more water releasing behaviour. Investigations of non-dewatered and dewatered specimens in the volume ratio of 1:1:2 (lime:brick dust:sand) showed that the addition of brick dust to lime mortar increased dewatering, which in turn led to greater compressive strength, carbonation depth, decreased porosity and depth of water penetration. These properties are of great importance in the conservation of historic masonry, as mortars that are too strong or possess low permeability can accelerate degradation. This study will enable identification of the most suitable mix designs thereby increasing the durability and prolonging the life of historic masonry.

Determining Water Transport Kinetics in Limestone by Dual-Wavelength Cavity Ring-Down Spectroscopy.

Water plays a major role in the deterioration of porous building materials such as those widely found in built heritage, influencing many physical, chemical, and biological decay processes. This article details a proof-of-principle study using near-infrared cavity ring-down spectroscopy (CRDS) to monitor the release of water and its artificially enriched isotopologues from small (ca. 25 × 25 × 5 mm) samples of limestone subject to drying by a fixed flow of nitrogen with varying levels of humidity and at room temperature and atmospheric pressure. Under low-humidity conditions, the drying kinetics are consistent with the well-established two-phase drying process exhibited by porous materials, namely, an initial constant drying rate period (phase I) followed by a falling drying rate period (phase II). The water diffusivity during phase II, DII, was measured (for Clipsham limestone) to be 3.0 × 10–9 ± 1 × 10–10 m2 s–1. The CRDS measurements allow spectroscopic determination of the total mass of water released by the sample, and the calculated values are in excellent agreement with gravimetric analysis. Importantly, the selectivity and sensitivity afforded by CRDS allows isotope analysis to be carried out, such that the flux of isotopically labeled water out of the sample can be determined under conditions of humidified flow where there may be a simultaneous ingress of water from the environment. Dual-wavelength CRDS distinguishes isotopic species, and it is demonstrated that the drying kinetics and physical properties of the samples are self-consistent when monitoring both HDO and H2O (for HDO, DII was 3.2 × 10–9 ± 4 × 10–10 m2 s–1). As the humidity levels in the flow increase, a departure from the distinct two-phase behavior is observed in the HDO drying curves. These new measurements of isotopically resolved mass fluxes will help refine models for drying mechanisms in porous media.

Water distribution and transport-kinetics model in fresh cement-based mixtures containing superabsorbent polymers based on 1H low-field NMR

Superabsorbent polymer (SAP) can be used as a curing agent in cement-based materials. Due to the replenish of humidity decline caused by the continuous consumption of water, the SAPs will contribute substantially to mitigating the shrinkage and obtaining the expected curing efficiency. Many studies have described the characteristics of water immigration in SAP-modified cement-based mixtures, but the travelled distance, volume, and transport-kinetics model of the water released from the SAP in cement-based materials still need to be investigated in detail. The paper focuses on the sustained water distribution of SAP at early-age cement-based mixtures. The swelling characteristics of SAP in different liquids and the water transport kinetics in hydrating cement-based mixtures were studied based on the ion concentration test and low-field Nuclear Magnetic Resonance (NMR) measurement. The results show that when SAP is in contact with water or cement filtrate, the exchangeable cations on the SAP structure will move freely to the solution and rapidly exchange with the metal cations in the solution within a few minutes (about 5 min). The most predominant form of water in fresh cement-based mixtures was the absorbed water (adsorbed on the surface of particles or in pores). Part of the adsorbed water or small capillary water on the surface of cement particles was consumed for hydration. The incorporation of SAP can prevent bleeding and segregation and promote the 28-day compressive strength of cement-based materials under the same total w/c ratio. Finally, the water-transport model in fresh cement-based mixtures was established and verified.

Use of brick waste for mortar-substrate optimisation of mortar-masonry systems

This paper investigates the effect of brick dust on the water-releasing properties and dewatering of hydrated lime mortars. Dewatering in masonry occurs when freshly mixed mortar is applied to a dry substrate (e.g. fired bricks, stone) and can influence the physical and mechanical properties of the mortar and the mortar-masonry bond. Controlling these properties provides an important opportunity to optimise performance. This study evaluates the water transport kinetics of hydrated lime-brick dust mortars. The study demonstrates that the particle size distribution of the brick dust can effectively control transfer sorptivity and dewatering time. The measured dewatering times correlated to theoretically calculated values demonstrating the ability to accurately predict the dewatering characteristics of a mortar from a knowledge of the mix design. The use of waste brick dust in hydrated lime mortars provides an environmentally friendly alternative to waste disposal by routes such as landfill.

Insights into the Control of Drug Release from Complex Immediate Release Formulations.

The kinetics of water transport into tablets, and how it can be controlled by the formulation as well as the tablet microstructure, are of central importance in order to design and control the dissolution and drug release process, especially for immediate release tablets. This research employed terahertz pulsed imaging to measure the process of water penetrating through tablets using a flow cell. Tablets were prepared over a range of porosity between 10% to 20%. The formulations consist of two drugs (MK-8408: ruzasvir as a spray dried intermediate, and MK-3682: uprifosbuvir as a crystalline drug substance) and NaCl (0% to 20%) at varying levels of concentrations as well as other excipients. A power-law model is found to fit the liquid penetration exceptionally well (average ). For each formulation, the rate of water penetration, extent of swelling and the USP dissolution rate were compared. A factorial analysis then revealed that the tablet porosity was the dominating factor for both liquid penetration and dissolution. NaCl more significantly influenced liquid penetration due to osmotic driving force as well as gelling suppression, but there appears to be little difference when NaCl loading in the formulation increases from 5% to 10%. The level of spray dried intermediate was observed to further limit the release of API in dissolution.

Water Sorption and Transport in Shales: An Experimental and Simulation Study

AbstractUnderstanding water uptake and drainage in shales has important implications for both hydrocarbon extraction and hydraulic fracturing fluid disposal. This study reports gravimetric water sorption isotherms and kinetics of water transport in shales. Moisture mass transport profiles during water uptake and drainage processes were numerically simulated. Quantitative parameters characterizing the water transport properties were calculated and their dependences on water saturation were analyzed. An approach was proposed to evaluate the permeability of shales using dynamic water sorption. The reliability of the estimated results was verified by the experimental values using gas permeability measurements.The apparent diffusion coefficients of water sorption on shales were found to be between 1.0 × 10−12 and 1.5 × 10−11 m2/s. The apparent diffusion coefficient first increases with water saturation and remains stable at a moderately saturated condition. However, this coefficient decreases for shales with high water saturation. Apparent diffusion coefficients for the sorption process are almost equal to those for the desorption process, except at the moderate saturation condition. Liquid water (including adsorbed water) contributes more than 80% to the water transport, whereas water vapor mainly contributes to shales with low water saturation. The liquid water permeability determined by water sorption is consistent with the crushed‐rock permeability measured by gas expansion. A further reasonable agreement is achieved between the analytical gas permeability, as a function of water saturation, and the experimental gas phase permeability. Water sorption kinetics provide an indirect method for assessing the water transport properties as a function of water saturation when direct measurements are not available.

Effect of immidazolium-based green solvents on the moisture absorption and thickness swelling behavior of wood flour/polyethylene composites

The water transport kinetics and moisture-induced thickness swelling behavior of wood-plastic composites (WPCs) in the presence of two imidazolium-based ionic liquids (ILs) were studied. The wood flour chemically treated with ILs were compounded through melt mixing of high-density polyethylene and coupling agent, and finally, the test specimens were produced by compression molding. Hygroscopic rates of the composites were evaluated by immersing them in the water at room temperature and monitoring moisture sorption and thickness changes for several weeks. Besides, the water diffusion coefficients and swelling rate parameters were measured for all composites. It was found that the water absorption and thickness swelling of the WPC specimens reduced as a result of ILs treatment. The SEM analysis revealed that the presence of ILs can improve the quality of adhesion between the polymer matrix and the cellulosic materials, to decrease the gaps in the interfacial region and block the hydrophilic groups. Studying the water sorption process in the specimens showed that the process follows kinetics and mechanisms described by Fick’s law. The highest water diffusion coefficients and swelling rate parameters were found in composites with untreated wood.

Effect of waiting time on the water transport kinetics of magnesium sulfate aerosol at gel-forming relative humidity using optical tweezers.

With the loss of water, the amorphous gel states in aqueous magnesium sulfate (MgSO4) aerosol forms and results in nonequilibrium dynamics, owing to the extended time scales for diffusive mixing. The mass transfer resistance in MgSO4 aerosol droplets during evaporation or condensation is investigated using aerosol optical tweezers (AOTs) coupled with Raman spectroscopy. In addition, the kinetics of water transport during hydration and dehydration after different waiting time is studied. With the cyclic change of the relative humidity (RH) below gel-forming, the waiting time is varied to examine the effect of the duration of drying and humidifying on water transport kinetics during subsequent hydration and dehydration process. Apparent diffusion coefficients (Dap) of water molecules in the gel state after different waiting time are obtained. The results indicate that the duration of drying will affect water transport kinetics for subsequent humidifying process due to the different structure and composition in MgSO4 aerosol droplet at different ambient humidities. However, the duration of humidifying has little effect on water transport kinetics for subsequent drying process below gel-forming RH.

Surface Plasmon Resonance Imaging: An Inexpensive Tool to Study the Water Transport in Thin Film PFSA Ionomers

The kinetics of water transport in confined thin film Perfluorinated sulfonic-acid (PFSA) ionomers is of vital importance in various applications such as a proton-exchange membrane or catalyst layers in polymer-electrolyte fuel cells. Advanced imaging techniques such as Neutron reflectivity, grazing-incidence x-ray scattering, and atomic force microscopy have been used for studying interfacial water transport in thin film ionomers. The instruments mentioned are considered high-end, expensive, super-resolution microscopes. The need for an expensive microscopic apparatus restricts many laboratories in developing countries from conducting experiments in the field of interfacial sciences such as visualization and in-situ measurement of water transport in thin film PFSA ionomers due to financial constraints, limited infrastructure, and lack of high-end technical support. Following the notion of portable and low-cost technologies, which is a vision of many researchers, we investigated the application of high-speed surface plasmon resonance imaging (SPRi) in the visualization of diffusion transport phenomena of water in thin film (7-250 nm) ionomers (Nafion and 3M). The preliminary results show that the water uptake in the thin film ionomers locally decreases the refractive index of the material, whose changes can be tracked by SPRi. This can provide the 3D map of diffusion during water transports through the thin film ionomer.

Interplay between Swelling Kinetics and Nanostructure in Perfluorosulfonic Acid Thin-Films: Role of Hygrothermal Aging

Impacts of processing, storage, and operation on thin-film perfluorosulfonic acid (PFSA) ionomer coatings used in electrodes of electrochemical devices remains unestablished. In this work, alteration of structure–function relationship in ionomers is achieved via exposure to elevated temperature and humidity (hygrothermal aging). Findings reflect a strong inverse correlation between aging-induced ionomer thin-film domain orientation and water-transport kinetics evaluated from swelling. Impact of aging is shown to be more pronounced on platinum due to interactions with PFSA, as evidenced by greater increase in nanodomain orientation parallel to substrate accompanied by reduced water transport, in contrast to silicon support.

Mechanics of mouse blastocyst hatching revealed by a hydrogel-based microdeformation assay

Mammalian embryos are surrounded by an acellular shell, the zona pellucida. Hatching out of the zona is crucial for implantation and continued development of the embryo. Clinically, problems in hatching can contribute to failure in assisted reproductive intervention. Although hatching is fundamentally a mechanical process, due to limitations in methodology most studies focus on its biochemical properties. To understand the role of mechanical forces in hatching, we developed a hydrogel deformation-based method and analytical approach for measuring pressure in cyst-like tissues. Using this approach, we found that, in cultured blastocysts, pressure increased linearly, with intermittent falls. Inhibition of Na/K-ATPase led to a dosage-dependent reduction in blastocyst cavity pressure, consistent with its requirement for cavity formation. Reducing blastocyst pressure reduced the probability of hatching, highlighting the importance of mechanical forces in hatching. These measurements allowed us to infer details of microphysiology such as osmolarity, ion and water transport kinetics across the trophectoderm, and zona stiffness, allowing us to model the embryo as a thin-shell pressure vessel. We applied this technique to test whether cryopreservation, a process commonly used in assisted reproductive technology (ART), leads to alteration of the embryo and found that thawed embryos generated significantly lower pressure than fresh embryos, a previously unknown effect of cryopreservation. We show that reduced pressure is linked to delayed hatching. Our approach can be used to optimize in vitro fertilization (IVF) using precise measurement of embryo microphysiology. It is also applicable to other biological systems involving cavity formation, providing an approach for measuring forces in diverse contexts.

Consequences of dewatering cement mortars incorporated with ground Bayburt stone

The detrimental effects of the rapid dewatering of cement mortars due to the interaction of wet mortar and brick substrate at the freshly mixed state in masonry construction are often addressed in the literature. The desorptivity and hence very high water releasing ability of cement mortars result in a great water loss during dewatering that significantly affects the fresh and hardened state properties of the end product. The paper therefore investigates the possible role of ground Bayburt stone incorporation in cement mortars on dewatering characteristics and the consequences of this effect at the hardened state properties of these mortars in construction practice. The paper begins with the measurement of the parameters of water transport kinetics and individually reports the effect of dewatering on the mechanical properties and durability characteristic of cement mortars incorporated with ground Bayburt stones. The results reported in this paper strongly suggest that ground Bayburt stone incorporation in cement mortars significantly compensate the degree of dewatering, and this vital feature does not only decreases the influence of dewatering on mechanical properties but also results in an enhanced durability characteristics of cement mortars.

Adrenomedullin improves fertility and promotes pinopodes and cell junctions in the peri-implantation endometrium.

Implantation is a complex event demanding contributions from both embryo and endometrium. Despite advances in assisted reproduction, endometrial receptivity defects persist as a barrier to successful implantation in women with infertility. We previously demonstrated that maternal haploinsufficiency for the endocrine peptide adrenomedullin (AM) in mice confers a subfertility phenotype characterized by defective uterine receptivity and sparse epithelial pinopode coverage. The strong link between AM and implantation suggested the compelling hypothesis that administration of AM prior to implantation may improve fertility, protect against pregnancy complications, and ultimately lead to better maternal and fetal outcomes. Here, we demonstrate that intrauterine delivery of AM prior to blastocyst transfer improves the embryo implantation rate and spacing within the uterus. We then use genetic decrease-of-function and pharmacologic gain-of-function mouse models to identify potential mechanisms by which AM confers enhanced implantation success. In epithelium, we find that AM accelerates the kinetics of pinopode formation and water transport and that, in stroma, AM promotes connexin 43 expression, gap junction communication, and barrier integrity of the primary decidual zone. Ultimately, our findings advance our understanding of the contributions of AM to uterine receptivity and suggest potential broad use for AM as therapy to encourage healthy embryo implantation, for example, in combination with in vitro fertilization.

Water transport kinetics and thickness swelling behavior of natural fiber-reinforced HDPE/CNT nanocomposites

Abstract This study mainly focused on investigating the effect of carbon nanotubes (CNTs) on the long-term hygroscopic behavior of composites based on old corrugated container (OCC) and high density polyethylene (HDPE). Composite profiles were made by melt compounding and then injection molding. For CNT as a reinforcing agent, different loading levels of 0, 1, 3 and 5 phc was used. The amount of HDPE and coupling agent was fixed at 50 wt% and 2 phc for all formulations, respectively. The governing kinetic behavior of water transport in the studied composites was examined by immersing them in water at room temperature for several weeks, and water diffusion coefficients were also calculated by evaluating the water absorption isotherms. In addition, a predictive model for determining the thickness swelling rate of the samples was developed by Shi and Gardner model. Results indicated that the composites filled with CNT had considerably lower water absorption compared with those samples without ones. The absorption processes for all families of composites were found to exhibit Fickian diffusion behavior. It was found that that equilibrium thickness swelling and also shorter equilibrium time (the time to reach the equilibrium thickness swelling) decreased with increase of CNT loading. Furthermore, the swelling model provided a good predictor of the hygroscopic thickness swelling process of HDPE/OCC/CNT hybrid composites. Also, a good linear relationship was fit between swelling rate parameter ( K SR ) and CNT contents. The minimum K SR values were observed in composites made of 5 phc CNT.

Effect of zeolite on dewatering, mechanical properties and durability of cement mortar

The possible effect of zeolite on water transport kinetics, mechanical properties and durability of cement mortars is investigated in this paper. The high desorptivity of cement mortars results in rapid dewatering when they are applied in the freshly mixed wet state to absorbent substrates in masonry construction. This paper particularly focuses on the dewatering that takes place due to the interaction of wet mortar and brick substrate in the freshly mixed state and the properties of cement mortars that are significantly influenced as a consequence of this interaction in the hardened state. The transfer sorptivity, time to dewater, setting time, consistence, strength and water penetration depth, along with the effect of dewatering on these parameters, were investigated not only for mortar/substrate optimisation in masonry construction but also for improved mechanical properties. The results obtained show that the ability to manipulate water transport kinetics and hence reduce mix-water loss during dewatering by using zeolite – a natural pozzolanic replacement material – is a vital feature of cement mortars not only for enhanced mechanical properties and durability but also for sustainable production of these mortars in construction practice.

A rapid scan vacuum FTIR method for determining diffusion coefficients in viscous and glassy aerosol particles.

We report a new method to investigate water transport kinetics in aerosol particles by using rapid scan FTIR spectroscopy combined with a custom-built pulse relative humidity (RH) control system. From real time in situ measurements of RH and composition using high time resolution infrared spectroscopy (0.12 s for one spectrum), and through achieving a high rate of RH change (as fast as 60% per second), we are able to investigate the competition between the gas and condensed phase diffusive transport limits of water for particles with mean diameter ∼3 μm and varying phase and viscosity. The characteristic time (τ) for equilibration in particle composition following a step change in RH is measured to quantify dissolution timescales for crystalline particles and to probe the kinetics of water evaporation and condensation in amorphous particles. We show that the dissolution kinetics are prompt for crystalline inorganic salt particles following an increase in RH from below to above the deliquescence RH, occurring on a timescale comparable to the timescale of the RH change (<1 s). For aqueous sucrose particles, we show that the timescales for both the drying and condensation processes can be delayed by many orders of magnitude, depending on the viscosity of the particles in the range 101 to 109 Pa s considered here. For amorphous particles, these kinetics are shown to be consistent with previous measurements of mass transfer rates in larger single particles. More specifically, the consistency suggests that fully understanding and modelling the complex microphysical processes and heterogeneities that form in viscous particles may not be necessary for estimating timescales for particle equilibration. A comparison of the kinetics for crystalline and amorphous particles illustrates the interplay of the rates of gas and condensed phase diffusion in determining the mass transport rates of water in aerosols.

Activating relaxation-controlled diffusion mechanisms for tailored moisture resistance of gelatin-based bioadhesives for engineered wood products

The feasibility of tailoring the moisture resistance of bioadhesives by activating relaxation-controlled diffusion mechanisms is demonstrated herein using gelatin, a hydrophilic biopolymer, as a model biobased resin for engineered wood products. The effect of gelatin-to-water concentration and tannin addition on the governing kinetics of water transport in gelatin-based bioadhesives was investigated in this work. Time-dependent flexural mechanical properties of laminated (a) gelatin and (b) gelatin–tannin wood veneer composites conditioned at both moderate and high humidity were characterized and compared to oriented strand board and plywood. Results indicate that increases in both gelatin and tannin content not only decrease rates of water uptake, volumetric swelling, and maximum moisture contents of gelatin-based resins, but also increasingly induce relaxation-controlled moisture diffusion behavior, which implies short-term moisture resistance and long-term moisture affinity. This behavior could be leveraged to address both in-service (i.e., strength, stiffness) and out-of-service (i.e., rapid biodegradation) requirements for engineered wood products.