Diffusion Coefficient Of Water Research Articles

Monolayer Amphiphiles Hydrophobicize MoS2-Mediated Real-Time Water Removal for Efficient Waterproof Hydrogen Detection.

Ensuring water-fouling-free operation of semiconductor-based gas sensors is essential to maintaining their accuracy, reliability, and stability across diverse applications. Despite the use of hydrophobic strategies to prevent external water intrusion, addressing in situ-produced water transport during H2 detection remains a challenge. Herein, we construct a novel waterproof H2 sensor by integrating single-atom Ru(III) self-assembly with monolayer amphiphiles embedded in MoS2. The unique monolayer structure enables the sensor to detect H2 in the presence of water, as well as facilitate the self-transport of in situ-generated water from the H2-O2 reaction during H2 detection. Molecular dynamics simulations reveal that monolayer amphiphiles exhibit a higher water diffusion coefficient than multilayer amphiphiles, making them more advantageous for removing in situ-produced water. Deployable on mobile platforms, it enables wireless H2cat detection for up to 6 months, without the introduction of protective membranes against dust and water ingress. This work not only enhances the performance of H2 detection but also introduces a new concept for the advancement of stable water-sensitive sensors.

Molecular diffusion in aqueous methanol solutions: The combined influence of hydrogen bonding and hydrophobic ends.

Although the nonmonotonic variation in the diffusion coefficients of alcohol and water with changing alcohol concentrations in aqueous solutions has been reported for many years, the underlying physical mechanisms remain unclear. Using molecular dynamics simulations, we investigated the molecular diffusion mechanisms in aqueous methanol solutions. Our findings reveal that the molecular diffusion is co-influenced by hydrogen bonding and the hydrophobic ends of methanol molecules. A stronger hydrogen bond (HB) network and a higher concentration of hydrophobic ends of methanol molecules both enhance molecular correlations, thereby slowing molecular diffusion in the solution. As methanol concentration increases, the HB network weakens, facilitating molecular diffusion. However, the increased concentration of hydrophobic ends counteracts this effect. Consequently, the diffusion coefficients of water and methanol molecules exhibit nonmonotonic changes. Previous studies have only focused on the role of HB networks. For the first time, we have identified the impact of the hydrophobic ends of alcohol on molecular diffusion in aqueous alcohol solutions. Our research contributes to a better understanding and manipulation of the properties of aqueous alcohol solutions and even liquids with complex compositions.

Molecular dynamics insights into the dynamical behavior of structurally modified water in aqueous deep eutectic solvents (ADES).

Recent studies have demonstrated that the presence of water in deep eutectic solvents (DESs) significantly affects their dynamics, structure, and physical properties. Although the structural changes due to the addition of water are well understood, the microscopic dynamics of these changes have been rarely studied. Here, we performed molecular dynamics simulation of 30% (v/v) (∼0.57 molar fraction) water mixture of DES containing CH3CONH2 and NaSCN/KSCN at various salt fractions to understand the microscopic structure and dynamics of water. The simulated results reveal a heterogeneous environment for water molecules in aqueous DES (ADES), which is influenced by the nature of the cation. The diffusion coefficients of water in ADESs are significantly lower than that in neat water and concentrated aqueous NaSCN/KSCN solution. When Na+ ions are replaced by K+ ions in the ADES system, the diffusion coefficient increases, which is consistent with the measured nuclear magnetic resonance data. Self-dynamic structure factor for water and other simulated dynamic quantities, such as reorientation, hydrogen-bond, and residence time correlation functions, show markedly slower dynamics inside ADES than in the neat water and aqueous salt solution. Moreover, these dynamics become faster when Na+ ions in ADES are replaced by K+ ions. The results suggest that the structural environment of water in Na+-rich ADES is rigid due to the presence of cation-bound water and geometrically constrained water. The medium becomes less rigid as the KSCN fraction increases due to the relatively weaker interaction of K+ ions with water than Na+ ions, which accelerates the dynamical processes.

Anomalous behaviour of transport properties in a supercooled water–glycerol mixture

Glycerol acts as a natural cryoprotectant by depressing the temperature of ice nucleation and slowing down the dynamics of water mixtures. In this work, we characterise dynamics – diffusion, viscosity and hydrogen bond dynamics – as well as density anomaly and structure of water mixtures with 1%–50% (w/w) glycerol at low temperatures via molecular dynamics simulations using all-atom and coarse-grained models. Simulations reveal distinct violations of the Stokes–Einstein relation in the low-temperature regime for water and glycerol. Deviations are positive for water at all concentrations, and positive for glycerol in very dilute solutions but turning negative in concentrated ones. The all-atom and coarse-grained models reveal an unexpected crossover in the dynamics of the 1% and 10 % (w/w) glycerol at the lowest simulated temperatures. This crossover manifests in the diffusion coefficients of water and glycerol, as well as in the viscosity and lifetime of hydrogen bonds in water. We interpret that the crossover originates on the opposing dependence with glycerol concentration of the two factors controlling the solutions' slow down: the increase in tetrahedrally coordinated water and the dynamics and clustering of the glycerol molecules. We anticipate that this dynamic crossover will also occur for solution of water with other polyols.

Characterization of Simulated Cytoplasmic Fluids

AbstractMolecularly crowded solutions have been used to simulate cytoplasmic fluids, but little justification is provided in the literature. This work compared three key physical properties of solutions containing polyethylene glycol and sucrose against those in the cytoplasmic fluid from bacteria Escherichia coli: fluid viscosity, relaxation time (T1 and T2) of water, and the diffusion coefficient of water. It was concluded that appropriate mixtures of sucrose and polyethylene glycol 10,000, such as 10% sucrose and 15% PEG10,000 and 7.5% sucrose and 19% PEG10,000, closely mimic these properties of cytoplasmic fluid from E. coli containing around 100 mg/mL of proteins.

Investigating intermittent immersion during osmotic dehydration of mango (Mangifera indica L. Moench). Part B mathematical modeling of D2I and D3I kinetics in mango (Mangifera indica L. Moench) slices

This work aims to investigate the dynamics of water loss (WL) and solute gain (SG) during dehydration impregnation by immersion (D2I) and intermittent immersion (D3I). WL and SG of mango slices, 4 × 1× 1 cm3 in size, during dehydration immersion impregnation (D2I) and dehydration impregnation by intermittent immersion (D3I) were determined at 35, 45 and 55 °C for 270 min. Mango slices were immersed in a hypertonic sucrose solution of (61.6 ± 0.2) °Brix at a ratio of 6 mL of hypertonic solution per gram of fruit. Five semi-empirical models, two of which have been modified, were used to study mass transfer during D2I and D3I, namely the Azura, Weibull, Crank, Modified Crank I, and Modified Crank II models. The equilibrium water loss (WL∞), the equilibrium solute gain (SG∞), the diffusion coefficient, and activation energy were determined using the Modified Crank II model which was the best of all the tested models. Equilibrium water loss during D2I decreased with increasing temperature, while during D3I it increased with temperature. The SG∞ during D2I and D3I increases with temperature but was higher in D2I than in D3I. The average water diffusion coefficients were (6.02 ± 2.62) × 10−8 m2 s−1 for D2I and (4.89 ± 0.55) × 10−8 m2 s−1 for D3I and the average solute diffusion coefficients were (4.45 ± 0.53) × 10−8 m2 s−1 for D2I and (8.33 ± 0.79) × 10−8 m2 s−1 for D3I. The activation energies for WL in D2I and D3I were respectively 38789 J mol−1 and 9503 J mol−1. The respective values for SG were 9037 J mol−1 and 7327 J mol−1. This work demonstrates that mass transfers in D3I are better than those in D2I, and it highlights that, unlike the D2I process, the D3I process is less sensitive to temperature variations, making it particularly advantageous for processing products with high nutritional value.

Understanding of Water Transport through Membrane Electrode Assembly in PEFC

In a polymer electrolyte fuel cell (PEFC), water generation, electroosmosis drag, and back diffusion change the humidity, which affects transport properties such as proton conductivity, effective oxygen diffusion coefficient, and permeance of the feed gas through a membrane. Since the sorption and desorption of water in the electrolyte membrane is slower than other processes such as the oxygen reduction reaction, the proton transport, and the oxygen diffusion, dynamic water behavior should be considered to estimate the cell performance precisely. In this study, the water permeation flux through a membrane electrode assembly (MEA) was measured, and the effective water diffusion coefficients in a membrane and catalyst layer (CL) were formulated as a function of temperature and the moisture content respectively. Dynamic moisture content change in MEA was simulated with the measured effective diffusion coefficients. The experimental results showed that desorption was slower than sorption in the identical moisture content range particularly at the beginning, and this tendency was successfully reproduced using the moisture content distribution obtained by numerical simulation.

Diffusion and sorption of water vapor by polyamide‐imides

AbstractThe study of sorption and diffusion characteristics of glassy polymers based on polyamide‐imides was carried out using the methods of static sorption, dilatometry, electron microscopy. Water sorption isotherms of polyamide‐imides based on trimellitimido‐N‐acetic acid (PAI‐A) and trimellitimido‐N‐p‐benzoic acid (PAI‐B) with different intramolecular ‘hinges’ in the diamine fragment were obtained. The isotherms are S‐shaped and occupy an intermediate position between polyheteroarylenes and aliphatic polyamides. The dual sorption model was used to interpret the results. It is shown that the Langmuir component of the isotherms is determined by the thermal prehistory of glassy polymers, while the sorption component associated with water dissolution according to Flory‐Huggins is determined by the chemical nature of the functional groups included in the monomeric unit. The diffusion coefficients of water and the temperature and concentration dependences of the diffusion coefficients of sorbed water molecules were determined.

Applied Electric Field Effects on Diffusivity and Electrical Double-Layer Thickness.

This study utilizes molecular dynamics (MD) simulations and continuum frameworks to explore electroosmotic flow (EOF) in nanoconfined aqueous electrolytes, offering a promising alternative to conventional micro-/nanofluidic systems. Although osmotic behavior in these environments is deeply linked to local fluid properties and interfacial dynamics between the fluid and electrolyte solutions, achieving a complete molecular-level understanding has remained challenging. The findings establish a linear relationship between electric field strength and fluid velocity, uncovering two distinct transport regimes separated by a critical threshold, with a markedly intensified flow in the second regime. It is demonstrated that rising electric field strengths significantly enhance water diffusion coefficients, supported by a detailed analysis of fluid hydration structures, the potential of mean force (PMF), and local stress tensors. Due to the applied electric field strength, the motion of ions and water accelerates, leading to the redistribution of ions and intensification of electrostatic forces. This expands the thickness of the electric double layer (EDL) and amplifies fluid diffusivity, thereby enhancing nanoscale fluid activity. These insights enhance the molecular-level understanding of EOF and define the stability of flow regimes, providing valuable guidelines for advancing nanofluidic technologies, such as drug delivery systems and lab-on-a-chip devices.

PNIPAM-based ionic hydrogels for enhanced privacy smart windows and flexible sensor

The thermochromic materials are widely used in the smart window field because they can efficiently regulate solar radiation with temperature changes. Currently, most smart windows switch back and forth between opaque and transparent states to control solar radiation, which is very disadvantageous for the visibility of enclosed environments. Herein, in a binary solvent of ethylene glycol-water (EW), we are developing a series of thermoresponsive ion hydrogels suitable for smart windows by in-situ free radical polymerization of the thermoresponsive monomer N-isopropylacrylamide (NIPAM) and ionic monomers (amphiphilic, anionic, cationic). These smart windows exhibit excellent one-way transparency for privacy protection, allowing observation from a relatively dark private space to a public space outside the smart window during the day, while preventing a view from the relatively bright public space into the private space. Furthermore, these hydrogels demonstrate efficient blocking of ultraviolet / near-infrared radiation, low temperature resistance (∼ −40 °C), wide temperature range thermal responsiveness (∼ −25–60 °C), enabling effective regulation of solar heat radiation. Additionally, the anionic-NIPAM complex hydrogel possesses a high diffusion coefficient of water and excellent conductivity of 13.38 mS cm−1, which can be expanded its application in the field of flexible ion-conductive sensors.

Effects of Osmotic Dehydration on Mass Transfer of Tender Coconut Kernel.

Tender coconut water has been very popular as a natural beverage rich in various electrolytes, amino acids, and vitamins, and hence a large amount of tender coconut kernel is left without efficient utilization. To explore the possibility of making infused tender coconut kernel, we investigated the effects of two osmosis methods, including solid-state osmotic dehydration and liquid-state osmotic dehydration, as well as two osmosis agents such as sorbitol and sucrose, on the mass transfer of coconut kernel under solid-state osmotic dehydration conditions. The results showed that under the conditions of solid-state osmosis using sucrose and liquid-state osmosis using sucrose solution, the water diffusion coefficients were 9.0396 h-1/2 and 2.9940 h-1/2, respectively, with corresponding water mass transfer coefficients of 0.3373 and 0.2452, and the equilibrium water loss rates of 49.04% and 17.31%, respectively, indicating that the mass transfer efficiency of solid-state osmotic dehydration of tender coconut kernel was significantly higher than that of liquid-state osmotic dehydration. Under solid osmosis conditions, the water loss rates using sucrose and sorbitol were 38.64% and 41.95%, respectively, with dry basis yield increments of 61.38% and 71.09%, respectively, demonstrating superior dehydration efficiency of sorbitol over sucrose under solid-state osmosis. This study can provide a reference for the theoretical study of the mass transfer of tender coconut kernel through osmotic dehydration, and also provide technical support for the development and utilization of tender coconut kernel.

Predicting anion diffusion in bentonite using hybrid machine learning model and correlation of physical quantities

Radionuclide diffusion will be influenced by numerous factors. Establishing a model that can elucidate the internal correlation between mesoscopic diffusion and the microscopic structure of bentonite can enhance the comprehension of radionuclide diffusion mechanisms. In this study, a light gradient boosting machine (LightGBM) was employed to predict the effective diffusion coefficients of HCrO4−, I−, and CoEDTA2− in bentonite. The model's hyperparameters were optimized using the particle swarm optimization (PSO) algorithm. Several correlated physical quantities, such as mesoscopic parameters (total porosity, rock capacity factor, and ion molar conductivity) and microscopic parameters (ionic radius and montmorillonite stacking number) were incorporated to develop a machine learning model that incorporated micro- and meso-scale features. The predictive performance of PSO-LightGBM was verified using diffusion experiments, which investigated the diffusion of HCrO4−, I−, and CoEDTA2− at compacted dry densities of 1200–1800 kg/m3 using a through-diffusion method. Spearman correlation and Shapley additive explanation analyses revealed that the compacted dry density, ionic diffusion coefficient in water, ionic radius, and total porosity were the top-four influencing factors among the 16 input features. Partial dependence plot analysis elucidated the relationship between the effective diffusion coefficient and each input feature. The analysis results were consistent with the experimental findings, demonstrating the reliability of machine learning. Due to the incorporation of multi-scale features, the PSO-LightGBM model demonstrated enhanced predictive accuracy, linking the microstructure of bentonite to radionuclide diffusion, and providing a comprehensive interpretation of the diffusion mechanism.

Comparative Analysis of Water-Induced Response in 3D-Printed SCF/ABS Composites under Controlled Diffusion

Additive manufacturing (AM) or 3D-printing of fiber-reinforced composites (FRCs) has garnered significant interests for its versatility in creating intricate parts and rapid prototyping due to cost-effectiveness. Although short fiber-reinforced thermoplastic composites are challenging to manufacture, their mechanical properties can be easily tailored by adjusting fiber type, orientation, and volume fraction. However, void formation during printing is a key issue, impacting mechanical properties and facilitating water ingression, affecting long-term durability. This work studies water diffusion characteristics and the associated hydro-aging of 3D-printed short carbon fiber (SCF)/acrylonitrile butadiene styrene (ABS) composites with controlled water diffusion. Effects of material type (ABS and SCF/ABS), 3D-printing path (horizontal and vertical filament orientation), and diffusion surface (uni-directional and bi-directional diffusion) on water diffusion coefficient and maximum water absorption level are characterized to ensure the long-term durability of 3D-printed ABS and SCF/ABS composites. Baseline representative volume element-based finite element (RVE-FE) diffusion models were developed based on micro-computed tomography (micro-CT) image analysis to understand water diffusion characteristics. This work proves that the SCF/ABS composite is more resistive to hydro-aging than neat ABS due to the SCFs’ hydrophobic nature. SCF/ABS composites, while providing distinct advantages over pure ABS in terms of mechanical properties, could also be more effective against water environments.

Thermochemical adsorption heat storage performance of functionalized UiO-66: Molecular simulation method

UiO-66 has broad application prospects in thermochemical adsorption heat storage owing to its great adsorption performance and stability. To further improve its performance, UiO-66 can be functionalized. Nevertheless, the adsorption and diffusion mechanism of UiO-66 and its functionalized structures is still unclear. Therefore, in this paper, it investigated the adsorption and diffusion performance of the UiO-66 series by molecular simulation. The effects of different functional groups were analysed, and the underlying mechanism was revealed. The results showed that adding –OH, –NH2, and –NH3+Cl- groups improved the adsorption capacity of UiO-66 at low pressure by 2.16, 3.22 and 4.25 times respectively, whereas adding –NO2 and −(OMe)2 groups reduced it by 46.05% and 86.84%. The adsorbent-water interaction was the strongest for UiO-66-NH3+Cl-, while UiO-66-(OMe)2 exhibited the weakest interaction. For the UiO-66 series, water molecules were preferentially adsorbed near the zirconium clusters, –OH, –NH2, and –NH3+Cl- groups. Then, they gradually filled around the organic ligands, and a very small amount gathered around the –NO2 and −(OMe)2 groups. Owing to the limitation of the pore volume, the water diffusion coefficient of all the structures initially increased and then decreased with the increase of water loading.

Decoupling Protein Concentration and Aggregate Content Using Diffusion and Water NMR.

Protein-based biopharmaceutical drugs, such as monoclonal antibodies, account for the majority of the best-selling drugs globally in recent years. For bioprocesses, key performance indicators are the concentration and aggregate level for the product being produced. In water NMR (wNMR), the use of the water transverse relaxation rate [R2(1H2O)] has been previously used to determine protein concentration and aggregate level; however, it cannot be used to separate between them without using an additional technique. This work shows that it is possible to "decouple" these two key characteristics by recording the water diffusion coefficient [D(1H2O)] in conjunction with R2(1H2O), even in the event of overlap in either D(1H2O) or R2(1H2O). This method is demonstrated on three different systems, following appropriate D(1H2O) or R2(1H2O) calibration data acquisition for a protein of interest. Our method highlights the potential use of benchtop NMR as an at-line process analytical technique.

Design of novel glass fiber reinforced polypropylene cable-anchor component and its long-term properties exposed in alkaline solution

The high performance and long life of engineering structures can be realized through replacing traditional steel materials with glass fiber reinforced polypropylene composites with high toughness/durability, flexibility design and recycling. In addition, the anchorage problem of composites needs to be solved by developing new anchorage technologies or forms. In the present paper, a new type cable-anchor component was developed to prolong the service life and realize the reliable anchoring of composite. The influence mechanism of arc angle (10°, 20°, and 30°) on the mechanical properties of cable-anchor component was evaluated through the experimental and mechanical simulation. The durability evolution of cable-anchor component exposed to alkali solution environment was investigated through macro-performance test and microstructure analysis. The results showed the tensile strength retention of cable-anchor component was up to 88.7 % at the arc angles of 10° under the circumferential constraint of carbon fiber. Larger arc angle increased the stress concentration and fiber misalignment of transition area between arc and straight segments, leading to the formation and propagation of defects or cracks in transition areas and early fracture failure. The saturated water absorption and diffusion coefficient of glass fiber reinforced polypropylene composites were obtained to be 0.78 % and 4.41×10−14 m2/s, respectively. Compared with nylon 6 and epoxy resin, polypropylene has excellent hydrophobic properties with the diffusion coefficient ratio of 0.0077 and 0.024. At the longest immersion, the tensile strength retentions of cable-anchor component were 61.8 % and the failure mode changed from component longitudinal splitting to brittleness fracture of arc region. The degradation mechanism was attributed to the initial defects of arc section formed and expanded under the complex stress and corrosive medium, which further aggravated the fiber/resin interfacial debonding. Through comparing with other glass fiber reinforced thermoplastic and thermosetting composites, the cable-anchor component has higher tensile strength retention after the immersion of alkaline solution owing to excellent hydrophobicity behavior of polypropylene and efficient preparation process.

Preparation of PVDF-nSiO2/PVSQ high-flux composite membrane by chemical grafting and separation of composite brine by membrane distillation

The large-scale application of membrane distillation (MD), an important method for desalting seawater, is limited due to membrane fouling. In this study, ethyl orthosilicate (TEOS) was polymerized to obtain different nSiO2 particles. Vinyl triethoxysilane (VTES) was hydrolysed and polycondensation was used to produce spherical polyethylene-sesquioxane (PVSQ) microparticles, which were modified to construct micro/nano particles. Then grafted on the surface of polyvinylidene fluoride (PVDF) composite membrane. The low-surface-energy hydrophobic groups present on the surfaces of the vinyl and ethoxy particles greatly enhanced the membrane hydrophobicity. The particle size of nSiO2 can change the properties of the membrane. The separation performance of the membrane was tested by direct contact membrane distillation (DCMD). In the separation of a constant concentration of feed solution (3.5 wt% NaCl), the membrane flux was relatively stable at 23.8 kg·m−2·h−1, and the salt interception rate reached 99.99 %. In the subsequent separation of a salt/humic acid solution, the flux remained stable and the good anti-fouling performance indicating that this system outperformed the unmodified membrane. Finally, the effect of different cations on the water diffusivity was studied using a molecular simulation method. Both Ca2+ and Mg2+ reduced the diffusion coefficient of water. However, when these two ions were present simultaneously, Ca2+ inhibited the binding of Mg2+ to water, and the diffusion coefficient of water increased. This study provides a novel approach for preparing hydrophobic membranes for the separation of complex brines.

Magnetic resonance imaging of tumor response to stroma-modifying pegvorhyaluronidase alpha (PEGPH20) therapy in early-phase clinical trials

Pre-clinical and clinical studies have shown that PEGPH20 depletes intratumoral hyaluronic acid (HA), which is linked to high interstitial fluid pressures and poor distribution of chemotherapies. 29 patients with metastatic advanced solid tumors received quantitative magnetic resonance imaging (qMRI) in 3 prospective clinical trials of PEGPH20: HALO-109-101 (NCT00834704), HALO-109-102 (NCT01170897), and HALO-109-201 (NCT01453153). Apparent Diffusion Coefficient of water (ADC), T1, ktrans, vp, ve, and iAUC maps were computed from qMRI acquired at baseline and ≥ 1 time point post-PEGPH20. Tumor ADC and T1 decreased, while iAUC, ktrans, vp, and ve increased, on day 1 post-PEGPH20 relative to baseline values. This is consistent with HA depletion leading to a decrease in tumor extracellular water content and an increase in perfusion, permeability, extracellular matrix space, and vascularity. Baseline parameter values predictive of pharmacodynamic responses were: ADC > 1.46 × 10−3 mm2/s (Balanced Accuracy (BA) = 72%, p < 0.01), T1 > 0.54 s (BA = 82%, p < 0.01), iAUC < 9.2 mM-s (BA = 76%, p < 0.05), ktrans < 0.07 min−1 (BA = 72%, p = 0.2), ve < 0.17 (BA = 68%, p < 0.01), and vp < 0.02 (BA = 60%, p < 0.01). A low ve at baseline was moderately predictive of response in any parameter (BA = 65.6%, p < 0.01 averaged across patients). These qMRI biomarkers are potentially useful for guiding patient pre-selection and post-treatment follow-up in future clinical studies of PEGPH20 and other tumor stroma-modifying anti-cancer therapies.

A Novel Numerical Model Considering Unsaturated Soil Properties and Computational Study on Heat and Moisture Transfer Characteristics of Helix Ground Heat Exchanger

Abstract A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover, the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam conditions, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.

The distinctions of the interfacial nanostructures and properties between carbon fiber reinforced fast and conventional curing epoxy composites subjected to hydrothermal treatments

The vital role of the interphase in loading transfer in carbon fiber reinforced resin composites has received considerable critical attention. In this study, to quantitatively distinguish between the effects of hydrothermal aging on the interfacial nanostructures and properties of carbon fiber reinforced fast and conventional curing epoxy composites, peak force quantitative nano-mechanics (PF-QNM) technique by atomic force microscopy (AFM) was utilized to determine the interfacial modulus, adhesion and thickness. In addition, the shear behavior was studied by short-beam strength test, and the water uptake was investigated by water adsorption test. Based on the modulus contrast of the interphase in PF-QNM modulus image, the average interfacial thickness of the fast curing epoxy composites after 18 h of hydrothermal aging was 67 nm, increased 236 % when compared with the unaged composites. It was much higher than the rise of 70 % of the conventional curing epoxy composites after 18 h of hydrothermal aging while the interfacial thickness was 69 nm. Consistently, the average interfacial thickness of the fast and conventional curing epoxy composites determined by the adhesion were 68 nm (widened 247 %) and 68 nm (widened 67 %). In a word, the interfacial thickness of the fast curing epoxy composites was about 4 times than that of the conventional curing epoxy composites after 18 h of hydrothermal aging, because of the fast curing caused microcracks and flaws. Then, after 192 h of hydrothermal aging, the decreasing of short-beam strength of the fast curing epoxy composites were almost 1.6 times than that of the conventional curing epoxy composites, due to the faster growing of microcracks and delamination on the side surface of the fast curing epoxy composites short-beam samples during testing. Lastly, the maximum water absorption and diffusion coefficient of the fast curing epoxy composites were 1.2 % and 5.5 × 10−7 cm2/s respectively, which were both 1.3 times that of the conventional curing epoxy composites. Significantly, all the results proved that, attributing to the fast curing caused microcracks and flaws in the fast curing epoxy composites, through which water preferred to enter a composite along the fibers and interphase, the interphase in the fast curing epoxy composites were more sensitive to the hydrothermal aging than the conventional curing epoxy composites. Therefore, the water uptake, interfacial thickness and short-beam strength of the fast curing epoxy composites changed faster.