Migration Of Water Molecules Research Articles

A molecular insight into asphalt-aggregate interfacial debonding: The role of hydrogen bonds in water molecule migration

In this study, molecular dynamics were employed to compare the angles, lengths, and numbers of hydrogen bonds between water molecules and different aggregates. Compared to quartz, calcite has shorter bond lengths, larger bond angles, and a greater number of bonds with water molecules. The differences in hydrogen bonds lead to the formation of a three-layer structure on the calcite surface by water molecules: ordered, relatively ordered, and disordered, while a two-layer structure—relatively ordered and disordered—is formed on the quartz surface. In the ordered layer, water molecules experience the strongest hydrogen bonding, are neatly arranged, and have low diffusion coefficients. In contrast, the disordered layer is characterized by weaker hydrogen bonding, random arrangement, and higher diffusion coefficients. The movement path of water molecules shows that the debonding of asphalt and aggregate is jointly influenced by the migration behavior of both the underlying and upper-layer water molecules. These findings reveal the microscopic mechanism of water molecules forming a wedge shape at the asphalt-aggregate interface from the perspective of hydrogen bonds, explaining why the constraint of water on the Calcite {214} and Calcite {018} surfaces is stronger compared to Calcite {1 0 4}, but the bonding energy with asphalt decays more rapidly.

Hydrogen Bond Network Shaping Proton Penetration Behavior across Two-Dimensional Nanoporous Materials.

In this study, we investigate aqueous proton penetration behavior across four types of two-dimensional (2D) nanoporous materials with similar pore sizes using extensive ReaxFF molecular dynamics simulations. The results reveal significant differences in proton penetration energy barriers among the four kinds of 2D materials, despite their comparable pore sizes. Our analysis indicates that these variations in energy barriers stem from differences in the hydrogen bond (HB) network formed between the 2D nanoporous materials and the aqueous environment. The HB network can be classified into two categories: those formed between the surface of the 2D nanoporous materials and the aqueous environment, and those formed between the edge atoms of the nanopores and the water molecules inside the pores. A strong HB network formed between the surface of the 2D nanoporous materials and the aqueous environment induces an orientational preference of water molecules, resulting in an aggregated water layer with high density. This high-density water region traps protons, making it difficult for them to escape and penetrate the nanopores. On the other hand, a strong HB network formed between the edge atoms of the nanopores and the water molecules inside the pores impedes the rotation and migration of water molecules, further inhibiting proton penetration behavior. To facilitate the proton penetration process, in addition to a sufficiently large pore size, a weak HB network between the 2D nanoporous material and the aqueous environment is necessary.

Improvement of casein / κ-carrageenan composite gel properties: Role of locust bean gum concentration

Processed cheese analogues (PCA) are popular among consumers worldwide for their diverse flavors and forms. Casein/κ-carrageenan (CA/KC), as the main structural basis of common PCA, suffers from syneresis and thermal instability, which could be well ameliorated by locust bean gum (LBG) as a thickening, non-gelatinizing polysaccharide. However, the mechanism by which LBG improves the gel properties of CA/KC composites has not yet been clarified. In this study, the CA/KC/LBG ternary composite gels were constructed and the effect of LBG concentrations (0–0.5%) on the CA/KC binary gel properties were investigated. Compared with the control CA/KC gel, the addition of low LBG concentrations (0.1–0.3%) significantly increased the water-holding capacity, strength and thermal stability of gels (P < 0.05), while the addition of high LBG concentrations (0.4%–0.5%) weakened the gel properties. To reveal the influence mechanism of LBG, the water migration, molecular interactions and microstructure of gels were compared. The results confirmed that the addition of LBG induced the migration of water molecules from free state to bound state and enhanced the hydrogen bonding interactions between CA/KC gel molecules. In addition, scanning electron microscopy results showed that the addition of low concentrations of LBG induced the unfolding of KC macromolecules into chains, which optimized the gel network structure of KC. The formed CA/KC/LBG ternary composite gels showed more homogeneous and denser gel network structure than the control. In conclusion, the addition of an appropriate amount of LBG could well improve the thermal stability of CA/KC binary gel and the sense of storage stability of PCA products.

Toward an Understanding of Uric Acid Particle Dissolution: Surface and Bulk-Driven Water Activity.

Uric acid particles contribute to kidney stones, and natural processes for the elimination of stones depend on solute-solvent interactions. The process of uric acid dissolution has previously been understood via the lens of solubility; however, for pure and mixed salt solutions, these approaches do not provide a comprehensive picture of nanoscale particle solution thermodynamics. Unlike solubility measurements, water activity measurements provide us with information about the chemical potential responsible for the migration of water molecules driving the dissolution of particles. In this work, we used in situ experimental tools to estimate water activity values for pure uric acid aqueous droplets at different stages of droplet growth. The process of cloud formation, i.e., water condensation on a solute particle resulting in aqueous droplet formation, was leveraged to compare the water affinity for nanosized uric acid particles with a well-studied inorganic salt, sodium chloride. Specifically, we investigated microscopic uric acid particles (nanoparticles <300 nm, amorphous and super micron particles >5 μm, crystalline) and the mechanism of water uptake. The growth of droplet volume (Growth Factor, GF) for uric acid particles is experimentally observed for supermicrometer crystalline particles (>1 μm) at subsaturated humidity conditions (<100% RH). In addition, the water activity of submicrometer-size uric acid particles is estimated under subsaturated and supersaturated humidity conditions. These measurements provide us with information about the volume growth of droplets as water condenses in particles exposed to different humidity conditions. Our observations under subsaturated humidity conditions show that the uric acid particles have limited volume growth (<1% change per volume and <10% change per volume for crystalline and amorphous measurement, respectively). From the experimental data, the affinity of uric acid solute with water as a solvent is quantified in terms of water activity.

Mechanism of sodium lauryl sulfate reducing froth stability of dodecylamine in hematite flotation: Experiments and molecular dynamics simulation

In this study, the influence of sodium lauryl sulfate (SLS) on the stability of dodecylamine (DDA) froth during the reverse flotation of hematite was investigated due to the frequent issue of excessively viscous foam leading to suboptimal reverse flotation outcomes. The research involved conducting flotation tests and two/three-phase froth stability assessments to explore how a specific molar ratio combination of DDA and SLS could enhance the flotation performance while simultaneously mitigating froth stability. The investigation into the mechanism by which SLS reduces the stability of DDA froth was aided by molecular dynamics simulations. The findings revealed that in the collector system comprising DDA and SLS, several key changes occurred at the molecular level. These included a decrease in the thickness of the electric double layer at the interface, a reduction in the thickness of the gas–liquid interface layer, weakening of the interaction strength between the head group and water molecules, a decrease in the coordination numbers of water molecules in the first hydration layer, and an enhanced migration ability of water molecules. Furthermore, there was an increased inclination angle between the head groups or molecular chains of the collector and the Z-axis, resulting in a diminished interaction depth between the head group and water and a closer positioning of the molecular tail chain to the gas–liquid interface with a more pronounced curvature. Consequently, these molecular adjustments led to a sparser arrangement of DDA molecules at the gas–liquid interface, lower coverage of the interface adsorption layer, and increased gas permeation, ultimately reducing DDA froth stability. The aforementioned conclusions provide a comprehensive molecular-level analysis of the principal mechanisms that can effectively reduce foam stability, including the attenuation of molecular head group-water interactions, reduction in gas–liquid interface layer thickness, decrease in gas–liquid interface orderliness, and enhancement of water molecule migration capability. The implications of this research extend to providing theoretical insights for addressing foam control challenges in DDA flotation processes.

A thermodynamic theory coupling photo-chemo-mechano interactions for light-responsive hydrogel

Light-responsive hydrogel, as a typical functional hydrogel, is composed of crosslinked hydrophilic polymer chains, photosensitive molecules and water. Under illumination, the photosensitive molecules exhibit a transition in hydrophilic/ hydrophobic properties, leading to migration of water molecules and deformation of the hydrogel based on the temporal and spatial distribution of light. In this study, we propose a nonequilibrium thermodynamic framework to study the photo-chemo-mechano behaviors of light-responsive hydrogel. We firstly describe the light propagation in the hydrogel and the photochemical reaction kinetics. New free energy functions to expound the relationship between the photochemical reaction and thermodynamic process are established, and the constitutive equations are derived. Subsequently, we implant the model into a multi-field coupling analysis software, COMSOL, to conduct a spatio-temporal analysis of the hydrogel's response under uniform light exposure. Finally, we simulate the inhomogeneous deformation of light-responsive hydrogel strips under different illumination conditions and compare the results with experiments. The results highlight the importance of the photochemical reaction rate and the redistribution of light field caused by deformation. The present research holds potential for the precise manipulation and optimal design of light-responsive hydrogel in prospective applications, and offers insights for the synthesis of similar materials as well as the design of pertinent devices.

Cementitous material based stabilization of soft soils by stabilizer: Feasibility and durabiliy assessment

To accurately assess the safety of excavation and its impact on deformation settlement in soft soil areas, it is essential to conduct stability analysis and investigate the solidification mechanism of improved soft soil. This study involved a comprehensive series of laboratory tests, such as direct shear, dry-wet cycles, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests, encompassing a wide range of working conditions. Based on the findings, an optimal construction scheme for solidifying the soil was proposed, utilizing data from the Zhuhai Tunnel project. The test results indicated that the curing time and proportion significantly influenced the shear strength of the amended soil. It was determined that a 10% cement and 9% stabilizer curing for 28 days represented the optimal proportion. The stabilizer primarily enhanced the shear strength by increasing the cohesion of the soil. Furthermore, the improved soil exhibited excellent stability even after undergoing seven dry-wet cycles. Additionally, microscopic analysis was conducted to explore the chemical reactions and solidification mechanism occurring between particles in the improved soft soil. The stabilizer induces the migration of water molecules to the soil surface and continuously supplies hydration to the cement, promoting its secondary hydration and generating more calcium silicate hydrate gel (C-S-H) and ettringite (AFt). The gelation and filling effects of the hydration products between particles resulted in a densified structure, thereby enhancing the mechanical strength and stability of the improved soil. This research offers valuable guidance for the application of soil improvement in construction and engineering projects in soft soil areas.

Effect of extruded wheat bran on the volatility and physical–chemical properties of bread during frozen storage

AbstractBackground and ObjectivesAt present, there are no sufficient data in the literature about the effect of extruded wheat bran on the volatility and physical–chemical properties of bread during frozen storage. Therefore, the current study aimed to investigate the effect of extruded wheat bran on the volatile components and physical–chemical properties of bread during frozen storage.FindingsFrozen storage could effectively extend the shelf‐life of bread. After 20 days of storage, the specific volume and cohesion of the control breads decreased significantly (2% and 21.55%, respectively). Moreover, the hardness and amylopectin retrogradation degree increased significantly (81.56%). After 30 days of storage, the amylopectin retrogradation degree of extruded wheat bran breads significantly increased (161%). After 40 days of storage, the cohesion of extruded wheat bran breads decreased significantly (7.67%). Extruded bran was conducive for improving bread stability during frozen storage. The transverse relaxation times (T2) of extruded wheat bran bread were shorter than those of the control bread. Bran inhibited water molecule migration and reduced the rate of bread quality deterioration. Further, 27 volatile components were detected in the control bread and 32 volatile components were detected in extruded wheat bran breads. The volatile components of all breads did not change significantly within the first 30 days of storage. Thereafter, the concentration of some volatile compounds decreased.ConclusionThe addition of extruded wheat bran significantly affected the volatility and physical–chemical properties of bread during frozen storage. The volatility and physical–chemical properties of extruded wheat bran bread changed gradually during frozen storage. The presence of bran inhibited water molecule migration and the formation and recrystallization of large ice crystals, and reduced the rate of bread quality deterioration during frozen storage.Significance and NoveltyThis study aimed to provide a reference for research on the storage and long‐term preservation of extruded wheat bran bread after production.

Inhalable Nitric Oxide Delivery Systems for Pulmonary Arterial Hypertension Treatment.

Pulmonary arterial hypertension (PAH) is a severe medical condition characterized by elevated blood pressure in the pulmonary arteries. Nitric oxide (NO) is a gaseous signaling molecule with potent vasodilator effects; however, inhaled NO is limited in clinical practice because of the need for tracheal intubation and the toxicity of high NO concentrations. In this study, inhalable NO-releasing microspheres (NO inhalers) are fabricated to deliver nanomolar NO through a nebulizer. Two NO inhalers with distinct porous structures are prepared depending on the molecular weights of NO donors. It is confirmed that pore formation can be controlled by regulating the migration of water molecules from the external aqueous phase to the internal aqueous phase. Notably, open porous NO inhalers (OPNIs) can deliver NO deep into the lungs through a nebulizer. Furthermore, OPNIs exhibit vasodilatory and anti-inflammatory effects via sustained NO release. In conclusion, the findings suggest that OPNIs with highly porous structures have the potential to serve as tools for PAH treatment.

Robust water diffusion modeling in a structural polymer joint based on experimental X-ray tomographic data at the micrometer scale

Structural bonding is a technique increasingly used in the industrial field. For applications in aggressive environments such as seawater, predicting the effect of moisture on the mechanical behavior of bonded assemblies is of paramount importance. The objective of this work is to analyze water diffusion in an epoxy adhesive material and, more specifically, to propose a robust method for choosing the most appropriate diffusion model. Experimental studies of the water absorption in a two-component epoxy structural adhesive, using gravimetry and X-ray tomography, were first performed. The presence of a population of pore-type defects in the polymeric joint helped to characterize the evolution of water diffusion kinetics. Thus, two diffusion mechanisms were identified: a first one related to the migration of water molecules within the adhesive matrix, and a second one related to the penetration of water into the pores. Then, Dual-Fick and Langmuir models were retained, as the two diffusion models most likely to capture the above mechanisms. Although it was shown that both models could give similar results in terms of global diffusion behavior, the results arising from these two models differ at the local scale, especially for extended periods of time. Therefore, special attention was paid to the second absorption mechanism, and a comparison of waterfronts between theoretical predictions and experimental tomographic data was achieved, leading to the final choice of a Dual-Fick diffusion model.

Multiscale deterioration of recycled aggregate gel network via solar irradiation: Reaction molecular dynamics and experiments

Nowadays, the efficient recycling of construction waste and the sustainability of recycled concrete have faced challenges due to the reduced performance of recycled aggregate (RA). One significant factor impacting the performance of RA is solar irradiation, which occurs throughout the entire service life of a construction project. However, the analysis of the effect of solar irradiation on hardened cement paste has not been fully addressed. This research presents a comprehensive investigation of the multi-scale deterioration of RA caused by solar irradiation. The dynamic evolution of the atomic and chemical structure of synthetic Calcium Silicate Hydrate (C-S-H) gel, the morphological changes in tricalcium silicate (C3S) hydration products, and the alteration of pore structure in the cement paste are unveiled through the combination of reactive molecular simulation and experimental approaches. The results indicate that solar irradiation disrupts the structure of C-S-H, leading to the migration of water molecules from the interlayer spaces of C-S-H to the pore spaces. This prompts the formation of a new, denser gel. However, as a consequence, more capillary pores are formed within the cement paste. The research outcomes provide a bottom-up, multi-scale insight into the reduced performance of RA under solar irradiation. Furthermore, the transmission mechanism of deterioration information at various scales is established, facilitating comprehension of the correlation between gel characteristics and macro-performance. This research paves the way for strategies to ameliorate the sustainability of recycled concrete, addressing the challenges associated with solar irradiation and enhancing the overall performance of recycled aggregate in concrete applications.

Adsorption of Multi-Collector on Long-Flame Coal Surface via Density Functional Theory Calculation and Molecular Dynamics Simulation

The quantum chemical properties of long-flame coal (LFC) and collectors (kerosene, diesel, diethyl phthalate (DEP), biodiesel collector (BDC), and emulsified biodiesel collector (EBDC)) were analyzed via the density functional theory (DFT). The molecular dynamics (MD) of the coal–collector–water system and the adsorption of collectors on LFC were conducted based on the first principles. The results showed that the frontier molecular orbitals of kerosene, diesel, DEP, and BDC were 0.38 eV, 0.28 eV, 0.27 eV, and 0.20 eV, respectively. The chemical reactivity order of the above mentioned collectors was BDC &gt; DEP &gt; diesel &gt; kerosene. Kerosene, diesel, and DEP adsorbed with carbonyl, hydroxyl, and carboxyl groups in LFC, respectively. Carboxyl groups in BDC and carboxyl groups in LFC bilaterally adsorbed, while BDC repelled water molecules via hydrogen bonds on the LFC surface. In the systems of BDC and EBDC, the diffusion coefficients of a water molecule were 2.83 × 10−4 cm2/s and 3.73 × 10−4 cm2/s. The emulsifier that adsorbed onto the oil–water interface of the coal–BDC–water system improved the dispersion of BDC during flotation, while at the same time increasing the number of hydrogen bonds between BDC and LFC, which accelerated the migration of water molecules from the LFC surface.

Behavior of the fullerene/water system under liquid and liquid–vapor conditions: A molecular dynamics approach

Classical molecular dynamics simulations were carried out to quantify the behavior of fullerenes in water, under liquid phase and liquid–vapor conditions. Different molalities of fullerene were considered in the study. Radial distribution functions, static dielectric constant and equation of state were evaluated in liquid phase. Direct liquid–vapor coexistence simulations of water with fullerene added were conducted to explore density profiles, liquid–vapor coexistence curve, pressure tensor components and surface tension variations with respect to water. An all-atom fullerene model studied by Monticelli and the SPC/ɛ description of water were used. At ambient conditions fullerene–fullerene and fullerene-water correlations decreased as molality increased. In turn, the static dielectric constant decreased due that fullerenes hinder the dipolar orientation of water molecules. As temperature increased, the static dielectric constant lowered. Part of the study was conducted at 373 K from 10 to 24 kbar, revealing that density of the system increased as molality was higher while fullerene-fullerene correlations decreased and fullerene-water correlations increased slightly. Concerning the static dielectric constant, a decrease was observed due that fullerenes and fullerene aggregates disturbed water structure as molality increased. As the system is compressed at a fixed molality, fullerenes become more uniformly distributed and the dielectric constant increases. Therefore, increasing the pressure is a mechanism to force the dipolar orientation of water molecules. On the other hand, liquid–vapor coexistence was studied from 280 to 650 K using molalities from 0.037 to 0.695 mol/kg. Liquid–vapor simulations revealed that the location of fullerenes and the formation of aggregates affect the behavior of surface tension. Fullerenes can locate at the liquid–vapor interfaces forming aggregates that obstruct the pass of water molecules to the vapor, so surface tension increases slightly with respect to water. At 0.695 mol/kg, larger clusters were observed but they located predominantly within the liquid phase and therefore acted in the opposite direction, that is, they favored the migration of water molecules to the vapor and surface tension dropped. In addition, a peculiar behavior was observed for temperatures above 500 K: surface tension increased its value as temperature increased. This behavior could be attributed to the fact that at such high molality the calculated surface tension might not longer correspond to liquid–vapor interfaces, instead it could be related to a sort of solid–liquid interface that have formed into the system. These calculations set the basis for improving the description of fullerene/water interactions as more experimental information becomes available and also serve as reference data in the design of interaction parameters to model water-soluble fullerenes.

Changes in water holding capacity of chilled fresh pork in controlled freezing-point storage assisted by different modes of electrostatic field action

Electrostatic field-assisted low-temperature preservation is considered a novel technology, which provides an effective means of extending the shelf-life of meat. This study aimed to investigate the effects of different output time modes of a high voltage electrostatic field (HVEF) on the water holding capacity (WHC) of chilled fresh pork during controlled freezing-point storage. Under a direct current HVEF generator, chilled fresh pork samples were treated by the single, interval, or continuous HVEF treatment, with a control check group receiving no HVEF treatment. It was determined that the WHC of the continuous HVEF treatment higher than the control check group. This difference was proven by analyzing the moisture content, storage loss, centrifugal loss, cooking loss, and nuclear magnetic resonance imaging. Furthermore, the mechanism behind HVEF-assisted controlled freezing-point storage reduced the moisture loss was conducted by examining the changes in the hydration characteristics of myofibrillar protein. The study revealed that myofibrillar proteins exhibit high solubility and low surface hydrophobicity under continuous HVEF. Additionally, continuous HVEF has been demonstrated to effectively maintain the higher WHC and lower hardness of myofibrillar protein gel by inhibiting the water molecule migration. The demonstration of these results showcases the effectiveness of electrostatic fields for the future physical preservation of meat.

Probing the Mechanism of Action of Small-Molecule Ice Recrystallization Inhibitors Using Proton Nuclear Magnetic Resonance Relaxation.

N-2-Fluorophenyl-d-gluconamide (2FA) improves the recovery and function of cryopreserved biological materials by inhibiting ice recrystallization. However, as for many small-molecule ice recrystallization inhibitors, the mechanism of action of 2FA is not well-understood. In this study, the IC50 of 2FA for ice recrystallization was determined to be 3.5 mM (95% CI [3.41-3.52]). 1H transverse and longitudinal relaxations were then characterized by NMR at 2FA concentrations from 0 to 10 mM and at temperatures between -15 °C and +30 °C. Corresponding activation energy of water molecule motion (EAH2O) was calculated, showing that at each concentration 2FA did not affect EAH2O in the solid state, whereas in the liquid state EAH2O was significantly higher with 2FA than for pure water. Therefore, 2FA is excluded from the ice lattice upon freezing and concentrated in the interstitial liquid phase. This restricts the migration of water molecules between ice crystals via the liquid phase, inhibiting ice recrystallization.

Ultrasonic Treatment of Corn Starch to Improve the Freeze-Thaw Resistance of Frozen Model Dough and Its Application in Steamed Buns.

Modification of corn starch using ultrasonic waves to improve its freeze-thaw resistance in frozen model doughs and buns. Analysis was performed by rheometry, low-field-intensity nuclear magnetic resonance imaging, Fourier infrared spectroscopy, and scanning electron microscopy. The results showed that the addition of ultrasonically modified corn starch reduced the migration of water molecules inside the model dough, weakened the decrease of elastic modulus, and enhanced the creep recovery effect; the decrease in α-helical and β-fold content in the model dough was reduced, the destruction of internal network structure was decreased, the exposed starch granules were reduced, and the internal interaction of the dough was enhanced; the texture of the buns became softer and the moisture content increased. In conclusion, ultrasound as a physical modification means can significantly improve the freeze-thaw properties of corn starch, providing new ideas for the development and quality improvement of corn-starch-based instant frozen pasta products.

Effect of natural zeolite on water distribution and migration in low water/binder cement-based composites (LW/B-CC) mixed with seawater: An experimental and computational investigation

This study focus on dynamic characteristics of water distribution and migration in low water/binder cement-based composites (LW/B-CC) mixed with seawater and natural zeolite based on experimental and numerical approaches. More exactly, micro/macro properties of LW/B-CC are investigated by experiments and then the mechanism of water migration is analyzed by molecular dynamics methodology. The results reveal that the internal curing effects reflected by 1H nuclear magnetic resonance (NMR) and shrinkage test indicate that porous zeolite alleviates the self-desiccation of LW/B-CC matrix, especially in seawater-mixed LW/B-CC. Besides, the use of seawater improves the interfacial transition zone (ITZ) between zeolite and matrix. Molecular dynamics simulations exhibit an enriched ion content at the zeolite-water interface, which tends to block the transportation of water molecules. Meanwhile, the migration of water molecules is more efficient in Na-heulandite induced by a more equal distribution of extra-framework charges. With evidence from experimental and numerical approaches, ions in seawater are confined by the lattice of zeolite, and more water can be stored in the pores of zeolite and used as internal curing water; hence, zeolite is an appropriate type of aggregate for producing LW/B-CC incorporating seawater.

Salt Hydrate Adsorption Material-Based Thermochemical Energy Storage for Space Heating Application: A Review

Recent years have seen increasing attention to TCES technology owing to its potentially high energy density and suitability for long-duration storage with negligible loss, and it benefits the deployment of future net-zero energy systems. This paper provides a review of salt hydrate adsorption material-based TCES for space heating applications at ~150 °C. The incorporation of salt hydrates into a porous matrix to form composite materials provides the best avenue to overcome some challenges such as mass transport limitation and lower thermal conductivity. Therefore, a systematic classification of the host matrix is given, and the most promising host matrix, MIL-101(Cr)(MOFs), which is especially suitable for loading hygroscopic salt, is screened from the perspective of hydrothermal stability, mechanical strength, and water uptake. Higher salt content clogs pores and, conversely, reduces adsorption performance; thus, a balance between salt content and adsorption/desorption performance should be sought. MgCl2/rGOA is obtained with the highest salt loading of 97.3 wt.%, and the optimal adsorption capacity and energy density of 1.6 g·g−1 and 2225.71 kJ·kg−1, respectively. In general, larger pores approximately 8–10 nm inside the matrix are more favorable for salt dispersion. However, for some salts (MgSO4-based composites), a host matrix with smaller pores (2–3 nm) is beneficial for faster reaction kinetics. Water molecule migration behavior, and the phase transition path on the surface or interior of the composite particles, should be identified in the future. Moreover, it is essential to construct a micromechanical experimental model of the interface.

Experimental Study and Molecular Simulation of the Effect of Temperature on the Stability of Surfactant Foam

Temperature changes in CO2 foam-fracturing construction can easily affect surfactant foam stability. To investigate the effect of temperature on the foam stability of different types of surfactants, this study measured the foam half-life and viscosity of four typical surfactants, CTAB, LAS-30, HSB1214, and TX-10, using a novel self-designed and built foam performance measurement device. The effects of temperature on foam half-life and viscosity were studied. The results show that as the temperature increased, the half-life shortened, and the viscosity of the liquid phase decreased, which led to a decrease in foam stability. Moreover, using Materials Studio, a type of molecular simulation software, an interfacial model of the foam film was constructed to calculate the IFE and the self-diffusion coefficient of water molecules at 300 ps after the equilibrium of the foam system to investigate the mechanism of temperature influence on the stability of the foam. The results show that, for CTAB, LAS-30, HSB1214, and TX-10, the temperature increases from 15 °C to 45 °C, the IFE is enhanced by −50.05%, −59.10%, −64.21%, and −44.26%, respectively, the interfacial system changes from a low-energy state to a high-energy state, and the interfacial stability decreases. Meanwhile, Dwater increased 1.10-fold, 0.78-fold, 1.43-fold, and 0.64-fold, respectively, which accelerated the diffusion and migration of water molecules, weakened the intermolecular forces, and accelerated the instability of the foam system.

The Mechanism for the Barrier of Lunar Regolith on the Migration of Water Molecules

AbstractThis paper reports the study of potential water retention mechanisms based on the migration process of water molecules in the lunar regolith. First, we propose innovative definitions for the adsorption barrier coefficient, the collision barrier coefficient, and the total barrier coefficient for water molecule migration in the lunar regolith. Second, we derive an equation that relates the different barrier coefficients. Finally, we develop an equation for the diffusion coefficient of water in the regolith. The results are as follows. The collision barrier coefficient is a function of the soil layer porosity and pore number density and increases with increasing pore number density and decreasing porosity. The adsorption barrier coefficient depends on the soil temperature, adsorption heat, porosity, and pore number density and decreases sharply with increasing temperature. The adsorptive capacity of lunar soil to adsorb water molecules increases with increasing the adsorption barrier coefficient. For soil layers with a lower temperature, adsorption plays a more important role than collision in hindering the migration of molecules in the regolith. The total barrier coefficient increases with decreasing temperature, increasing adsorption heat, decreasing porosity, and increasing pore number density. Our results suggest that the water loss rate is inversely proportional to the total barrier coefficient. The water loss rate decreases with decreasing soil temperature, increasing adsorption heat, decreasing porosity, and increasing pore number density. Namely, water is more likely to be retained in areas where the regolith has a low temperature, large adsorption heat, and both low porosity and large pore number density.