Intrinsic Diffusion Research Articles

Revealing membrane integrity and cell size from diffusion kurtosis time dependence.

The nonmonotonic dependence of diffusion kurtosis on diffusion time has been observed in biological tissues, yet its relation to membrane integrity and cellular geometry remains to be clarified. Here we establish and explain the characteristic asymmetric shape of the kurtosis peak. We also derive the relation between the peak time , when kurtosis reaches its maximum, and tissue parameters. The peak shape and its position qualitatively follow from the adiabatic extension of the Kärger model onto the case of intra-cellular diffusivity time-dependence. This intuition is corroborated by the effective medium theory-based calculation, as well as by Monte Carlo simulations of diffusion and exchange in randomly and densely packed spheres for various values of permeability, cell fractions and sizes, and intrinsic diffusivity. We establish that is proportional to the geometric mean of two characteristic time scales: extra-cellular correlation time (determined by cell size) and intra-cellular residence time (determined by membrane permeability). When exchange is barrier-limited, the peak shape approaches a universal scaling form determined by the ratio . Numerical simulations and theory provide an interpretation of a specific feature of kurtosis time-dependence, offering a potential biomarker for in vivo evaluation of pathology by disentangling the functional (permeability) and structural (cell size) integrity in tissues. This is relevant as the time-dependent diffusion cumulants are sensitive to pathological changes in membrane integrity and cellular structure in diseases, such as ischemic stroke, tumors, and Alzheimer's disease.

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The CYGNO experiment aims to build a large (O(10)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {O}(10)$$\\end{document} m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^3$$\\end{document}) directional detector for rare event searches, such as nuclear recoils (NRs) induced by dark matter (DM), such as weakly interactive massive particles (WIMPs). The detector concept comprises a time projection chamber (TPC), filled with a He:CF4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} 60/40 scintillating gas mixture at room temperature and atmospheric pressure, equipped with an amplification stage made of a stack of three gas electron multipliers (GEMs) which are coupled to an optical readout. The latter consists in scientific CMOS (sCMOS) cameras and photomultipliers tubes (PMTs). The maximisation of the light yield of the amplification stage plays a major role in the determination of the energy threshold of the experiment. In this paper, we simulate the effect of the addition of a strong electric field below the last GEM plane on the GEM field structure and we experimentally test it by means of a 10 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 10 cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document} readout area prototype. The experimental measurements analyse stacks of different GEMs and helium concentrations in the gas mixture combined with this extra electric field, studying their performances in terms of light yield, energy resolution and intrinsic diffusion. It is found that the use of this additional electric field permits large light yield increases without degrading intrinsic characteristics of the amplification stage with respect to the regular use of GEMs.

Thermal diffusivity measurement of polymer microfibers while eliminating the effect of heat radiation

The thermal transport properties of polymer fibers are important for heat dissipation in apparel, matrix of wearable devices, and so on. However, it is difficult to precisely determine the thermal properties of a single polymer fiber because of non-negligible thermal radiation due to its relatively low thermal conductivity and high surface-area-to-volume ratio. Here, we developed a system in which the apparent thermal diffusivity and size of microfibers can be measured to estimate their intrinsic thermal diffusivity. We determined the thermal diffusivities of three fibrous materials: silk, spider silk, and cellulose microfibers to be 4.2 (±0.8)×10−7, 1.8 (±0.7)×10−7, and 4.7 (±0.5)×10−7, respectively. For all fibers, the apparent thermal diffusivity strongly depended on the fiber size, indicating that eliminating the radiation effect is indispensable for determining the thermal transport properties of polymer microfibers.

Machine-learning-assisted deciphering of microstructural effects on ionic transport in composite materials: A case study of Li7La3Zr2O12-LiCoO2

The effective diffusivity of ionic species in multiphase materials is critical for the design and function of composite materials for electrochemical energy storage. In practice, effective diffusivity depends sensitively not only on the intrinsic diffusivities of constituting materials but also on their topological arrangement; nevertheless, these coupled contributions are oversimplified in most analytical models. Here, we combine atomistically informed mesoscale modeling and machine learning (ML) analysis to unravel how such features affect effective diffusivity in two-phase composites. Using the Li7La3Zr2O12-LiCoO2 composite solid-state battery cathode as a model system, we compute effective diffusivity for 600 distinct dense polycrystalline microstructures with different topological configurations of grains, grain boundaries, and heterointerfaces. We verify that in addition to atomic-scale variabilities, microstructural feature diversity can significantly impact effective transport properties. Across the ensemble of test microstructures, this often results in bimodal distributions of effective diffusivity that encompass two qualitatively distinct operating mechanisms, which we identify via flux analysis. An ML approach reveals that the most critical determining factors for effective diffusivity are the connectivity of bulk phases and their heterointerfaces. The role of ionic mobility at the heterointerfaces is also discussed. These insights highlight the combined importance of microstructure and interface engineering in tuning the transport properties of ionic species in composite materials. Our framework can also be extended for understanding generic microstructure-property relationships in other complex multiphase materials.

Improving diffusion kinetics of zinc ions/stabilizing zinc anode by molecular slip mechanism and anchoring effect in supramolecular zwitterionic hydrogels

The severe hydrogen evolution reaction and parasitic side reaction on Zn anode are the key issues which hinder the development of aqueous Zn-based energy storage devices. Herein, a polyacrylamide/carboxylated cellulose nanofibers/betaine citrate supramolecular zwitterionic hydrogels with molecular slip effects are proposed for enhancing Zn2+ diffusion and protecting Zn anodes. Non-covalent interactions within supramolecular hydrogels forms the skeleton for molecular slip and the strong coordination of carboxyl and amino groups with Zn2+ further facilitates the rapid Zn2+ transfer. Additionally, anchoring carboxyl and amino groups at the anode promotes the uniform deposition of Zn2+and protects Zn anode. On the basis of molecular slip mechanism and anchoring effect in the supramolecular zwitterionic hydrogels, Zn||Zn symmetric batteries undergo 800 h of stable electroplating stripping at a depth of discharge of 80 %. Zn||Cu asymmetric batteries exhibit an impressive average coulombic efficiency of 99.4 % over a remarkable span of 900 cycles at a current density of 15 mA cm−2. Furthermore, Zn||NH4V4O10 batteries successfully undergo over 1,000 cycles at a current density of 0.5 A g−1. Intrinsic ion diffusion mechanism of supramolecular hydrogel electrolytes provides an original strategy for the application of high-performance Zn-based energy storage devices.

Hydrogen interactions with intrinsic point defects and hydrogen diffusion in tungsten doped Al2O3

In light of the extensive use of tungsten (W) in fusion experimental devices and the importance of hydrogen isotopes permeation, based on the first principle approaches we study the effects of W doping on the formation energies of intrinsic point defects, hydrogen interactions with such defects, and hydrogen diffusion in bulk of α-Al2O3. Our investigation demonstrated that W doping enhances the formation of oxygen and aluminum vacancies (Vo and VAl) in α-Al2O3. In W doping α-Al2O3, hydrogen primarily exists in the form of Ho− (hydrogenation of the bulk VO3−) and Hi− (H interstitial) defects, while it hardly occupies VAl. Hydrogen is firmly trapped by Vo with a formation energy −3.35eV, and Hi− diffusion become extremely challenging because W doping significantly raises the Hi− diffusion barrier to 4.44 eV. Our findings indicate that W doping is beneficial for hydrogen permeation resistance in α-Al2O3.

Hexagonal MoO3 Anode with Extremely High Capacity and Cyclability for Lithium-Ion Battery: A Combined Theoretical and Experimental Study.

It is essential and still remains a big challenge to obtain fast-charge anodes with large capacities and long lifespans for Li-ion batteries (LIBs). Among all of the alternative materials, molybdenum trioxide shows the advantages of large theoretical specific capacity, distinct tunnel framework, and low cost. However, there are also some key shortcomings, such as fast capacity decaying due to structural instability during Li insertion and poor rate performance due to low intrinsic electron conductivity and ion diffusion capability, dying to be overcome. A unique strategy is proposed to prepare Ti-h-MoO3-x@TiO2 nanosheets by a one-step hydrothermal approach with NiTi alloy as a control reagent. The density functional theory (DFT) calculations indicate that the doping of Ti element can make the hexagonal h-MoO3-x material show the best electronic structure and it is favor to be synthesized. Furthermore, the hexagonal Ti-h-MoO3-x material has better lithium storage capacity and lithium diffusion capacity than the orthogonal α-MoO3 material, and its theoretical capacity is more than 50% higher than that of the orthogonal α-MoO3 material. Additionally, it is found that Ti-h-MoO3-x@TiO2 as an anode displays extremely high reversible discharge/charge capacities of 1326.8/1321.3 mAh g-1 at 1 A g-1 for 800 cycles and 611.2/606.6 mAh g-1 at 5 A g-1 for 2000 cycles. Thus, Ti-h-MoO3-x@TiO2 can be considered a high-power-density and high-energy-density anode material with excellent stability for LIBs.

Fractional dynamics of entropy generation in unsteady mixed convection of a reacting nanofluid over a slippery permeable plate in Darcy–Forchheimer porous medium

AbstractThis paper presents a theoretical investigation of the inherent irreversibility in unsteady fractional time derivative mixed convection of a reacting nanofluid with heat and mass transfer mechanism over a slippery permeable plate embedded in a Darcy–Forchheimer porous medium. The model fractional partial differential equations are obtained based on conservation laws and numerically solved using the implicit finite difference scheme. The study displays and discusses the effects of various emerging parameters on the overall flow structure, such as velocity profiles, temperature distribution, nanoparticles concentration profiles, skin friction, Nusselt number, Sherwood number, entropy generation rate, and Bejan number. It was found that an increase in dimensionless time and fractional parameters leads to a decrease in both the entropy generation rate and the Bejan number. The study revealed that fractional order derivatives can capture intrinsic memory effects, non‐local behaviour, and anomalous diffusion in the nanofluid flow process. This can ultimately lead to better engineering system design and control.

Multi-output multi-physics-informed neural network for learning dimension-reduced probability density evolution equation with unknown spatio-temporal-dependent coefficients

The Dimension-Reduced Probability Density Evolution Equation (DR-PDEE) offers a promising approach for evaluating probability density evolution in stochastic dynamical systems. Physics-Informed Neural Networks (PINNs) are well-suited for solving DR-PDEE due to their ability to encode physical laws into the learning process. However, challenges arise from the spatio-temporal-dependence of unknown intrinsic drift and diffusion coefficients, which drive DR-PDEE, along with their derivatives. To address these challenges, a novel framework called Multi-Output Multi-Physics-Informed Neural Network (MO-MPINN) is proposed to predict the evolution of time-varying coefficients and response probability density simultaneously. MO-MPINN features multiple output neurons, eliminating the necessity for distinct identification of unknown spatio-temporal-dependent coefficients separately. It uses parallel subnetworks to reduce training complexity and embeds multiple physical laws in the loss function to ensure an accurate representation of the underlying principles. Leveraging automatic differentiation, MO-MPINN efficiently computes derivatives of coefficients without resorting to numerical differentiation. The framework is applicable to high-dimensional stochastic nonlinear systems with double randomness in structural parameters and excitations. Several structures are presented to validate the performance of the MO-MPINN. This study introduces a new paradigm for solving partial differential equations involving differentiation of spatio-temporal-dependent coefficients.

Thermodynamic, Structural and Surface Properties of Liquid Al-Sr Alloy at Different Temperatures

Thermodynamic functions like excess Gibbs free energy of mixing (∆GxsM) and activity (a) of liquid Al-Sr alloy were studied in the temperature range 1323-1623 K in the frame work of Redlich-Kister (R-K) polynomial. The compositional and temperature dependence of structural functions like concentration fluctuation in long wavelength limit (Scc(0)), Warren-Cowley short range order parameter (α) and ratio of mutual to intrinsic diffusion coefficients (Dm/Did) were computed and analysed using the same approach. The surface tension (σ) and surface segregation (xsi) tendencies of the atoms in the liquid mixture were computed and studied using Butler’s model. Present investigations revealed that association tendency among the atoms of metallic mixture gradually decreased with increase in temperature.

Thermodynamic, structural, surface and transport properties of Au-Cu melt

Thermodynamic, structural, surface and transport properties of Au-Cu liquid alloy were calculated on the basis of different theoretical modeling equations. The thermodynamic properties, such as excess Gibbs free energy of mixing, enthapy of mixing and activity were estimated and compared with the available experimental and literature data on the basis of simple theory of mixing (STM). The best fit values of model parameters were estimated using the experimental values of excess Gibbs free energy of mixing and enthalpy of mixing of the system at 1550 K. Using the same model parameters and frame, the concentration fluctuation in long wave-length limit and Warren-Cowley short range order parameter were calculated and analysed to understand the local arrangement of atoms in the liquid mixture. The surface tension and extent of surface segregation of atoms in the initial melt were computed using Butler’s model. In transport properties, the ratio of mutual to intrinsic diffusion coefficients was calculated using STM and viscosity was calculated using Kaptay equation. The system showed complete ordering tendency at its melting temperature.

Introducing concepts of estimating tracer and intrinsic diffusion coefficients in a ternary system: a case study in the FCC Fe-Mn-Cr solid solution

ABSTRACT Estimating tracer and intrinsic diffusion coefficients following the diffusion couple method with systematic composition variation can be challenging because of the diffusion paths’ serpentine or double serpentine nature on the Gibbs triangle. Moreover, the possibility of estimating these diffusion coefficients from a single diffusion profile can have immense benefits. We have demonstrated four ways of estimating tracer and impurity diffusion coefficients in the FCC Fe-Mn-Cr solid solution: (i) We have shown that these can be estimated directly at the Kirkendall marker plane from a single conventional ternary diffusion profile. (ii) We have, for the first time, demonstrated that the estimation at the intersection of a conventional ternary and constrained pseudo-binary diffusion path is helpful for systematically generating composition-dependent tracer diffusion coefficients. (iii) We have followed the Kirkaldy-Lane method for estimating these diffusion coefficients at the intersection of two conventional ternary diffusion couples (for comparison of the data measured by new methods), although for data generation at random compositions. This was proposed a long time ago but practised occasionally. It helps to compare with the estimated data following other methods. (iv) Additionally, we have estimated the impurity diffusion coefficients of Cr and Mn in Fe following the Hall method, which helps in understanding the variation of the diffusion coefficients in Fe-Mn-Cr alloys compared to pure Fe. The sensitivity of data estimation following different methods, i.e. different equation schemes, is discussed, explaining the strategic design of diffusion couple for a small error range.

Surface engineering of Li3V2(PO4)3-based cathode materials with enhanced performance for lithium-ion batteries working in a wide temperature range

Operating at extreme temperatures is the biggest challenge for lithium-ion batteries (LIBs) in practical applications, as both the capacity and cycling stability of LIBs are largely decreased due to the sluggish reaction kinetics of the cathodes. Therefore, developing suitable cathode materials is the key point to tackling this challenge. Lithium vanadium phosphate [Li3V2(PO4)3, LVP] is a promising cathode with good features of a high working voltage, high intrinsic ionic diffusion coefficiency, and stable olivine structure in a wide temperature range, although it is perplexed by the low electronic conductivity. To tackle this issue, a series of nitrogen-doped carbon network (NC) coated LVP composites were synthesized using a hydrothermal-assisted sol-gel method. Among them, the LVP@NC-0.8 sample exhibited a remarkable tolerance at a high charging cutoff voltage of 4.8 V in a wide temperature range. Full cells of LVP@NC-0.8||graphite exhibited superior performance at different current rates. Moreover, the reaction mechanism of the LVP@NC-0.8 electrode was proved by in-situ X-ray diffraction technique, demonstrating that temperature was a critical factor that contributed to the sluggish phase transformation with high voltage hysteresis at low temperature and severe crystal structure distortion at high temperature. Theoretical calculations further demonstrated the superiority of the NC for high electronic conductivity and reduced lithium transportation barriers. The enhanced electrochemical performances of LVP-based cathode materials have provided the possible application of LIBs in a wide temperature range.

Calculation of grain boundary diffusion coefficients in γU-Mo using atomistic simulations

The γU-Mo alloy has been selected for the conversion of U.S. High-Performance Research Reactor (HPRR) fuel from highly enriched uranium to low enriched uranium as a part of the effort to reduce nuclear proliferation risks. Although γU-Mo alloys have the advantage of high uranium density and good overall irradiation performance, the irradiation-induced swelling and creep in the metal remain important design parameters since they influence the mechanical and thermal integrity of the fuel. To account for these design criteria, engineering scale models need fundamental properties, such as diffusion coefficients, as input. In this study, the diffusion of related species along grain boundaries in γU-Mo fuel is quantified considering that grain boundaries act as sinks for point defects, nucleation sites for gas bubbles, avenues for Coble creep, etc. The diffusivities of U and Mo in selected grain boundaries of γU-Mo alloys (γU-7Mo, γU-10Mo, and γU-12Mo) are obtained utilizing molecular dynamics simulations for a temperature range of 600 K - 1200 K with an interval of 100 K. The structures analyzed include symmetric tilt, asymmetric tilt, and twist grain boundaries. The grain boundary diffusion coefficients of U and Mo in the examined γU-Mo alloys are on the order of 10−14 to 10−11 m2s−1. It is observed that the U diffusivity in the grain boundary is higher than the Mo diffusivity in all cases and that the increase in Mo content of the alloy correlates to a decrease in the grain boundary diffusion. Xe diffusion along γU-10Mo grain boundaries is also calculated in this work, and the diffusivity of Xe in the γU-10Mo grain boundaries is found to be 8 to 15 orders of magnitude higher than the intrinsic Xe diffusivity in γU-10Mo depending on the temperature. The information gathered in this work can inform fuel swelling and creep models and help understand various other phenomena related to γU-Mo fuel performance.

Single-file diffusion and its influence on membrane gas separation: A case study on UTSA-280

Gas permeation in metal-organic framework-based (MOF-based) membranes is often elucidated through the solution-diffusion model, where the adsorption and diffusion of gases play equally vital roles. This study draws attention to a unique phenomenon known as single-file diffusion (SFD) occurring within MOF membranes that possess ultramicropores with dimensions comparable to the gas molecules themselves. When SFD takes place, the separation performance becomes solely reliant on the adsorption quantities on the feed side of the membrane. As a proof of concept, we fabricated a UTSA-280 membrane and subjected it to testing using gas mixtures of CO2/N2 and CO2/CH4. Two crucial observations substantiate the occurrence of single-file diffusion. Firstly, in the gas mixtures, the diffusion coefficients of N2 or CH4 were observed to align closely with that of CO2, despite the intrinsic diffusion coefficients of CO2, N2, and CH4, as determined from single-gas permeation experiments, exhibiting differences. Secondly, the CO2 mole fractions within the adsorption phase closely mirrored those in the gas phase on the permeate side. Given the high adsorption selectivity of UTSA-280 for CO2, the UTSA-280 membrane delivers outstanding permeation selectivity for CO2/N2 (611) and CO2/CH4 (80.7). Our experimental findings are supported by mesoscale kinetic Monte Carlo simulations, which confirmed the relation between the CO2 compositions in the adsorption phase on the feed side and in the gas phase on the permeate side. Furthermore, density functional theory calculations revealed high energy barriers associated with CO2 surpassing its counterparts, rendering such processes unfavorable, thereby reinforcing our experimental findings regarding single-file diffusion.

Modulating spin current induced effective damping in β–W/Py heterostructures by a systematic variation in resistivity of the sputtered deposited β–W films

Utilizing the spin-induced pumping from a ferromagnet (FM) into a heavy metal (HM) under the ferromagnetic resonance (FMR) condition, we report an enhancement in effective damping in β- W/Py bilayers by systematically varying resistivity (ρ W ) of β-W films. Different resistivity ranging from 100 μΩ-cm to 1400 μΩ-cm with a thickness of 8 nm can be achieved by varying the argon pressure (P Ar ) during the growth by the method of sputtering. The coefficient of effective damping α eff is observed to increase from 0.010 to 0.025 with ρ W , which can be modulated by P Ar . We observe a modest dependence of α eff on the sputtering power (p S ) while keeping the P Ar constant. α eff dependence on both P Ar and p S suggests that there exists a strong correlation between α eff and ρ W . It is thus possible to utilize ρ W as a tuning parameter to regulate the α eff , which can be advantageous for faster magnetization dynamics switching. The thickness dependence study of Py in the aforementioned bilayers manifests a higher spin mixing conductance ( geff↑↓ ) which suggests a strong spin pumping from Py into the β-W layer. The effective spin current (J S(eff)) is also evaluated by considering the spin-back flow in this process. Intrinsic spin mixing conductance ( gW↑↓ ) and spin diffusion length (λ SD ) of β-W are additionally investigated using thickness variations in β-W. Furthermore, the low-temperature study in β-W/Py reveals an intriguing temperature dependence in α eff which is quite different from α b of single Py layer and the enhancement in α eff at low temperature can be attributed to the spin-induced pumping from Py layer into β-W.

An experimental estimation method of diffusion coefficients in ternary and multicomponent systems from a single diffusion profile

Until recently, it was textbook knowledge that the diffusion coefficients could not be estimated in a multi-component system following the widely practised diffusion couple method. The recently proposed constrained diffusion couple method largely solved the problems. The need to produce two intersecting diffusion paths in a multi-component space with very well-controlled compositions of the diffusion couple end members may be tricky in certain situations, depending on the complications of diffusion paths. In this study, we have shown the estimation of all types of diffusion coefficients from a single diffusion profile without neglecting Onsager's cross terms in concentrated ternary Ni-Co-Fe, Fe-rich quaternary Fe-Ni-Co-Cr and concentrated Ni-Co-Fe-Cr-Al quinary alloys. This is applicable in ternary and multicomponent component systems (n≥3) at a stable Kirkendall marker plane position. One can even estimate the impurity diffusion coefficients utilizing the composition profiles at the ends of the diffusion couples following the Hall method, which has been rarely practised in multicomponent systems until now. We have further demonstrated the importance of estimating the tracer and intrinsic diffusion coefficients in a concentrated or multi-principal element alloy in which interdiffusion coefficients can be vague and misleading for understanding the elements' diffusional interactions and relative mobilities. We have also shown the importance of considering the vacancy wind effect in concentrated alloys. The method proposed in this study will help to generate a mobility database with relative ease in various multicomponent systems important for various applications, which was considered impossible until recently.

A scaling rule for power output of salt hydrate tablets for thermochemical energy storage

Salt hydrates are thermochemical materials capable of storing and releasing heat through reversible reaction with water vapor. In a heat battery, salt hydrate tablets of millimeter size are necessary to ensure a sufficient permeability of the packed bed. A profound understanding of the hydration process of these tablets is required to improve their kinetic performance. In this study we show that the hydration timescale of salt tablets is transport limited and that it depends primarily on the porosity and on the driving force (Δp). From gravimetric measurements done on SrBr2·6H2O and CaC2O4 we derived the intrinsic reaction and effective diffusion coefficients (k and Deff) and found that they validate a front-diffusion limited hydration hypothesis. In particular, the obtained Deff values (0.8–4.5 mm2 s−1) only depend on the tablets' porosities. Based on these parameters, we calculated the second Damköhler number (DaII) and proved that many other hydration reactions are diffusion limited. In the case of identical structures, the power output is therefore controlled only by the driving force. Its variation could be predicted by calculation of a so-called power scaling factor (Λ) for a selection of salts. This power scaling factor depends on the enthalpy (ΔH) and entropy (ΔS) of the reaction. For a temperature output of 40 °C and at 12 mbar most hydration reactions fall in the interval 0<Λ<30 and Λ exceeds 30 only in very few cases. This parameter establishes therefore another important constraint to the selection of the most ideal salt. Suitable strategies to circumvent the diffusion limitation will lead to the development of next generation salt hydrate tablets for thermochemical energy storage.

Modelling a gas injection experiment incorporating embedded fractures and heterogeneous material properties

This study focuses on the modelling of a gas injection experiment to assess the effects of incorporating heterogeneous material properties. The numerical model considers a two-phase flow coupled hydro-mechanical problem, and includes embedded fractures that open with deformation, thereby enhancing permeability. The approach used is integrated in the CODE_BRIGHT software, which allows for the consideration of geomaterials with a spatially correlated heterogeneous field of porosity that follows a normal distribution. This spatial correlation can be either isotropic or anisotropic. A key aspect of this approach is that material properties such as intrinsic permeability, diffusivity or cohesion are defined as a function of porosity. Consequently, these properties also exhibit heterogeneity with spatial correlation and, eventually, anisotropy. The results derived from the numerical model align well with in-situ measurements. The study also includes sensitivity analyses to the variation of critical variables. The calibration of the model has been validated through a similar experiment. The findings indicate that the consideration of heterogeneous material properties can have a significant influence on gas injection problems, particularly when a hydraulic fracture is formed.

Intrinsic Water Transport in Moisture-Capturing Hydrogels.

Moisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel-salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.