Diffusion Coefficient Of Water Molecules Research Articles

Water structure at coal/water interface: Insights from SFG vibrational spectroscopy and MD simulation

The coal/water interface plays a significant role in coal processing and utilization, and hydrogen bonds (HBs) are the primary factors affecting the interfacial water structure. Sum frequency generation (SFG) vibrational spectroscopy was used in this study to analyze HBs at the coal/water interface, and molecular dynamics (MD) simulations were conducted to investigate the molecular dynamics properties of interfacial water. The results showed that water molecules formed strong HBs with the lignite surface using both oxygen and hydrogen atoms, whereas HBs at bituminous coal/water and anthracite/water interfaces mainly occurred through the hydrogen atoms of water molecules. Fewer HBs existed at the bituminous coal/water interface, resulting in more free hydroxyl groups of water molecules. HBs at the anthracite/water interface were weaker than those at the lignite/water interface but stronger than those at the bituminous coal/water interface. Stronger HBs facilitated the adsorption of water molecules onto coal surfaces, reducing the number density and diffusion coefficient of water molecules within the water layer. For both properties, the MD simulation results showed the following order of decreasing magnitude: bituminous coal/water interface > anthracite/water interface > lignite/water interface. The combination of SFG vibrational spectroscopy and MD simulation offers a scientific approach to understanding the coal/water interface.

Analysis of the influence of ions on degradation of benzamide with hydrodynamic cavitation technology

In recent years, hydrodynamic cavitation technology has become a research hotspot in various fields. This study establishes a benzamide model with different ion types, ion concentrations, and bubble radii. The model is used to study the diffusivity of water molecules on the benzamide wall and structural changes in benzamide. The influence of ion type, ion concentration, and bubble radius on the degradation of pollutants is examined. The results are as follows: the larger the bubble radius and ion concentration, the larger the rate of change of maximum radial distribution function of carbon atoms (w). The effect of ion type on the diffusion coefficient of water molecules on the benzamide wall is as follows: H2O2 > HCO3−1 > NO3−1. In terms of structural changes in the benzamide, in the model containing H2O2, ion concentration has a greater effect than bubble radius. In the model containing HCO3−1, bubble radius has a greater effect than ion concentration. In the model containing NO3−1, bubble radius and ion concentration have an equal effect. w decreases most in the model containing H2O2 and least in the model containing NO3−1. The model containing H2O2 produces the most powerful effect in benzamide pollutant degradation. This study provides technical guidance and a theoretical basis for the green treatment of pollutants using cavitation theory.

Molecular simulation study of the influence of different surfactants on the wetting characteristics of anthracite

The reduction of dust pollution in coal mines is of great importance both for protection of the environment and for the occupational safety and health of coal mine workers. The reduction of dust from anthracite has been a challenge due to its inherent hydrophobicity and high metamorphism. As a result, surfactants are commonly added to water to improve the wettability of coal, thereby improving the dust reduction efficiency of a water spray system. To clarify from a microscopic perspective the effect of different surfactants on the wettability of anthracite, models for the anthracite-surfactant-water system were established, and adsorption configuration, relative concentration distribution, and the diffusion coefficients of water molecules in the systems were thoroughly investigated with molecular simulations. The results showed the directional arrangement of surfactants in the simulation systems after 150 ps of equilibration, resulting in the reduced surface tension of the water-surfactant solution and enhanced wettability of anthracite. Along the (001) normal direction, the relative concentration of sodium dodecylbenzenesulfonate (SDBS) (15.32), the anthracite-water overlapping area, the diffusion rate of water molecules, and the activity (DSDBS = 0.97 × 10-8 m2·s−1) were maximized, indicating the excellent wettability effect of SDBS. The results of the study are of practical significance for improving the wetting effect of anthracite, improving the dust reduction efficiency, and safeguarding the occupational safety and health of personnel.

Study on the damage mechanism of moisture intrusion to the FRP/RPUF interface of composite cross-arms when considering the influence of temperature

Moisture is more likely to infiltrate the FRP/RPUF interface with relatively weak internal insulation of composite insulated cross-arms in humid and hot working environments, leading to interface degradation. However, the damage mechanism after water infiltration into the FRP/RPUF interface under temperature conditions remains unclear. This study conducted moisture infiltration experiments and explored the damage mechanism after moisture infiltration into the FRP/RPUF interface under the influence of temperature using molecular dynamics simulations. The moisture absorption process at the FRP/RPUF interface is divided into two stages: Fick or Langmuir moisture absorption and physical moisture absorption. During the Fick or Langmuir moisture absorption stages, increased temperature enhanced the diffusion coefficient of water molecules and accelerated the moisture absorption rate of the material. Simultaneously, the proportion of bound water to free water in the system decreased, increasing the free volume fraction within the material. As the equilibrium between bound and free water was reached, the system could accommodate more moisture, thereby increasing the saturation moisture absorption capacity of the interface material. During the physical moisture absorption stage, increased temperature accelerated the decomposition rate of the material, intensifying the degree of interface bonding failure. Simultaneously, the thermal motion of the water molecules became more vigorous, increasing the influx of moisture into the sample through interface cracks. Consequently, the moisture absorption capacity and rate of the sample increased.

A computational investigation of DMSO/water separation through functionalized GO multilayer nanosheet membrane using molecular dynamics simulation and deep neural network model for membrane performance prediction

In this molecular dynamics (MD) simulation study, the separation of dimethyl sulfoxide (DMSO) from water was investigated using multilayer functionalized graphene oxide (GO) membranes. The GO nanosheets were modified with chemical groups (-F, -H) to alter their properties. The study analyzed the influence of pressure and functional groups on the separation rate. Additionally, a deep neural network (DNN) model was developed to predict membrane behavior under different conditions in water treatment processes. Results revealed that the fluorine-functionalized membrane exhibited higher permeation compared to the hydrogen-functionalized one, with potential of mean force (PMF) analysis indicating higher energy barriers for water molecules passing through the hydrogen-functionalized membrane. The study used density profile, water density map analysis, and radial distribution function (RDF) analysis to understand water and DMSO molecule interactions. The diffusion coefficient of water molecules was also calculated, showing higher diffusion in the fluorine-functionalized system. Overall, the findings suggest that functionalized GO membranes are effective for DMSO-water separation, with the fluorine-functionalized membrane showing superior performance. The DNN model accurately predicts membrane behavior, contributing to the optimization of membrane separation systems.

Anticorrosion mechanism of FACs-GO hybrids in ER coatings by EIS and MD simulation

To explore the enhancement of corrosion resistance and the microscale anti-corrosion mechanism of the epoxy resin (ER) composite coatings, this study prepared ER composite coatings using fly ash microbeads (FACs) and graphene oxide (GO) as fillers, conducted immersion corrosion experiments, and characterized the corrosion resistance of the coatings using electrochemical impedance spectroscopy (EIS). The experimental results showed that the FACs-GO/ER composite coating immersed for 7 days exhibited an impedance modulus three orders of magnitude higher than that of the pure ER coating. Furthermore, molecular dynamics (MD) simulations were carried out to calculate the interaction energy between ER matrix and fillers, free volume, and water molecule diffusion coefficient. It is revealed by MD simulations that the FACs-GO hybrid filler combined the performance advantages of both FACs and GO fillers, significantly improving dispersibility and compatibility within the ER matrix. The hybrid/ER composite material exhibited the lowest free volume, indicating enhanced densification of the ER material. The diffusion coefficient of water molecules in the FACs-GO/ER composite MD model decreased, indicating that the hybrid filler effectively enhanced the barrier properties of the ER composite coating against corrosive media. Therefore, the excellent dispersibility and shielding adsorption of FACs-GO hybrid fillers improved the corrosion resistance of the coating and revealed the microscale corrosion resistance mechanism of FACs-GO hybrid fillers in ER coatings.

Interactions between fluorocarbon surfactant and coal dust at macro, meso and molecular scales and their applications in coal dust control

Surfactants play an important role in the field of coal dust prevention, among which fluorocarbon surfactants have the advantages of low surface tension and have the potential to become mine dust suppressants. In this study, the wettability of fluorocarbon surfactant (OBS) on coal dust was studied from macro experiments, meso dust mist coupling and micro molecular simulation. The results showed that the surface tension of 0.06% OBS was as low as 17.6 mN/m, and the median particle size of coal dust reached 60.25 μm after wetting coal dust. Coal dust particles are easier to bond with each other into large particles, thus promoting settlement; During the meso collision between droplets and coal dust particles, OBS droplets showed excellent wetting and spreading effect, and the droplet state was stable, and the optimal spraying velocity was determined to be 20–30 m/s; At the molecular level, the diffusion coefficient of water molecules in the OBS system is minimally 0.46 Å2/ps, indicating a strong ability to constrain water molecules. The strength and energy of the hydrogen bonds formed with water molecules were greater than those of hydrocarbon surfactants, resulting in the best adsorption of water molecules. Additionally, it was found that the law of attractive and competitive adsorption of different surfactants in wetting coal dust is based on the difference in positive and negative electrostatic potential, where the greater the difference, the stronger the interaction. This provides a theoretical reference for judging the wetting performance of different surfactants at the molecular level.

Characterization of the wetting properties of ionic liquids on lignite surfaces: Molecular dynamics simulations

In order to study the wetting mechanism of imidazole ionic liquids on lignite surfaces, molecular dynamics simulations combined with quantum chemistry were used to analyze the molecular level of 1-butyl-3-methylimidazolium chloride salt ([Bmim][Cl]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF4]) adsorption and wetting processes on the surface of lignite molecules. The electrostatic potentials and frontline orbital energy levels of [Bmim][Cl], [Bmim][BF4], and [Emim][BF4] and coal molecular models were analyzed to determine their nucleophilic and electrophilic regions based on the density flooding theory (DFT) in Gaussian 09 program. The water-coal system and ionic liquid–water-coal system were constructed from a microscopic perspective by dynamics simulations, and the relative concentration distribution of each system in the z-axis direction, the diffusion coefficients of water molecules in each system, and the non-bonding interactions of each system were analyzed. The results showed that [Emim][BF4] has the largest front-line orbital energy polarity and the best wettability for coal. [Emim][BF4] was more likely to interact with water molecules to form hydrogen bonds and had the highest number of hydrogen bonds with water molecules. The molecular dynamics simulations revealed that the adsorption of ionic liquids on the surface of lignite increased the adsorption thickness between water-coal systems, which led to a more extensive diffusion of water molecules, which increased the negative interaction energy between water-modified lignite and further improved the hydrophilicity of lignite, with [Emim][BF4] molecules having the strongest ability to improve the hydrophilicity of lignite. These results further demonstrated that [Bmim][Cl], [Bmim][BF4], and [Emim][BF4] can significantly improve the wettability of coal dust, which was important for improving the effect of coal seam water injection and reducing the dust concentration.

Pathway for Water Transport through Breathable Nanocomposite Membranes of PEBAX with Ionic Liquid [C12C1im]Cl.

Water transport through membranes is an attractive topic among the research dedicated to dehydration processes, microenvironment regulation, or more simply, recovery of freshwater. Herein, an atomistic computer simulation is proposed to provide new insights about a water vapor transport mechanism through PEBAX membranes filled with ionic liquid (IL) [C12C1im]Cl. Starting from experimental evidence that indicates an effective increase in water permeation as the IL is added to the polymer matrix (e.g., up to 85·10-3 (g·m)/(m2·day) at 318.15 K for PEBAX@2533 membranes loaded with 70% of IL), molecular dynamics simulations are proposed to explore the key role of IL in water transport inside membranes. The polar region composed of anions and cationic head groups of the IL is demonstrated to serve as the pathway for water transport through the membrane. Water molecules always stay near the pathway, which becomes wider and thus has a larger water-accessible area with increasing IL concentration. Hence, the diffusion coefficients of water molecules and ions increase as the IL concentration increases. The simulation provides useful indications about a microscopic mechanism that regulates the transport of water vapor through a kind of PEBAX/IL membrane, resulting in full agreement with the experimental evidence.

Structure and properties of montmorillonite containing Ca2+, Sr2+, and Ba2+ cations simultaneously

Most raw montmorillonites (MMT) used for radioactive waste disposal (HLW) contain Ca in the interlayer space. When HLW and MMT come into contact, various ions, such as Sr2+ and Ba2+, enter the mineral. Therefore, the article presents the results of modeling, based on molecular dynamics, for four different models for the replacement of part of Ca2+ with Sr2+ and Ba2+ ions in Ca-MMT.The general trend of MMT swelling does not change significantly after the introduction of Sr2+ and Ba2+ ions. The diffusion coefficient of water molecules increases with an increase in the number of H2O layers between mineral layers or the presence of a certain amount of large radius ions in the series Ca-MMT, Ca-Ba-MMT, Ca-Sr-MMT, Ca-Sr-Ba-MMT. It shown that in the state of single-layer clay hydration, all the studied cations form outer-sphere complexes. During two-layer clay hydration, Ca2+ tends to form outer-sphere complexes, while Sr2+ and Ba2+ ions predominantly form inner-sphere complexes. With a further increase in the number of water molecules, the interaction of Ca2+ with the basal surface of the MMT mineral layer increases.

Scalable Fabrication of Superhydrophobic Coating with Rough Coral Reef-Like Structures for Efficient Self-Cleaning and Oil-Water Separation: An Experimental and Molecular Dynamics Simulation Study.

Superhydrophobic coating has a great application prospect in self-cleaning and oil-water separation but remains challenging for large-scale preparation of robust and weather-resistant superhydrophobic coatings via facile approaches. Herein, this work reports a scalable fabrication of weather-resistant superhydrophobic coating with multiscale rough coral reef-like structures by spraying the suspension containing superhydrophobic silica nanoparticles and industrial coating varnish on various substrates. The coral reef-like structures effectively improves the surface roughness and abrasion resistance. Rapid aging experiments (3000h) and the outdoor building project application (3000 m2 ) show that the sprayed superhydrophobic coating exhibits excellent self-cleaning properties, weather resistance, and environmental adaptability. Moreover, the combined silica-coating varnish-polyurethane (CSCP) superhydrophobic sponge exhibits exceptional oil-water separation capabilities, selectively absorbing the oils from water up to 39 times of its own weight. Furthermore, the molecular dynamics (MD) simulation reveals that the combined effect of higher surface roughness, smaller diffusion coefficient of water molecules, and weaker electrostatic interactions between water and the surface jointly determines the superhydrophobicity of the prepared coating. This work deepens the understanding of the anti-wetting mechanism of superhydrophobic surfaces from the perspective of energetic and kinetic properties, thereby paving the way for the rational design of superhydrophobic materials and their large-scale applications.

Synergistic effects of dodecane-castor oil acid mixture on the flotation responses of low-rank coal: A combined simulation and experimental study

The utilization of an appropriate collector or surfactant is crucial for the beneficiation of low-rank coal. However, in previous studies, the selection of surfactants was primarily based on flotation procedures, which hinders the understanding of the interaction mechanism between surfactant groups and oxygen-containing functional groups at the surface of low-rank coal. In this study, we investigate the flotation of low-rank coal in the presence of a composite collector by using a combined theoretical and experimental approach. The maximum flotation mass recovery achieved was 82.89% using a 3:1 mixture of dodecane and castor oil acid. Fourier-transform infrared and X-ray photoelectron spectroscopic analyses showed that castor oil acid was effectively adsorbed onto the surface of low-rank coal, enhancing the hydrophobicity of the coal. In addition, the diffusion coefficient of water molecules in the water-composite collector-coal system was greater than that in the dodecane system. Moreover, due to the presence of castor oil acid in the flotation process, the adsorption distance of dodecane and low-rank coal became shorter. Molecular dynamics simulations revealed that the diffusion and interaction of surfactant molecules at the interface of low-rank coal particles and water was enhanced because the adsorption of the dodecane-castor oil acid mixture is primarily controlled by hydrogen bonds and electrostatic attraction. Based on these results, a better surfactant for flotation of low-rank coal is also proposed.

Molecular Dynamics Study on Mechanical Properties of Cellulose with Water Molecules Diffusion Behavior at Different Oxygen Concentrations

Six groups of cellulose-water-oxygen simulation models with oxygen concentrations of 0%, 2%, 4%, 6%, 8%, and 10% were established by molecular dynamics software to analyze the effect of oxygen concentration on the mechanical properties of wood cellulose during water vapor heat treatment in terms of the number of hydrogen bonds, the diffusion coefficient of water molecules, the mean square displacement of cellulose chains, and mechanical parameters. The results showed that the diffusion coefficient of water molecules increased steadily as oxygen concentration increased, which affected cell size and density to some extent. The mean square displacement of the cellulose chain at a higher oxygen concentration was larger than at a lower oxygen concentration, indicating that the cellulose chain became more unstable at high oxygen concentration. This trend was consistent with the amount of hydrogen bonds inside the cellulose chains. The analysis of mechanical parameters showed that Young’s modulus and shear modulus showed a trend of increasing and then decreasing with increasing oxygen concentration, and wood cellulose had good resistance to deformation and rigidity at 2% oxygen concentration. Therefore, during the heat treatment of wood, appropriately increasing the oxygen concentration will potentially improve the rigidity and distortion resistance of wood.

Molecular Study of Nonequilibrium Transport Mechanism for Proton and Water in Porous Proton Exchange Membranes

The transport process of proton and water through a porous proton exchange membrane (PEM) under pressure difference is significant to fuel cell performance. Nonequilibrium molecular dynamics simulations were conducted to investigate the diffusion mechanisms of hydronium ions and water molecules under pressure differences. Here, different driving forces (0.15 kcal/(mol·Å)–0.45 kcal/(mol·Å)) were applied to hydronium ions and water molecules as they transported through Nafion 117 membrane at temperatures between 300 K and 350 K. Results indicated that the transport diffusion coefficient of water molecules was larger than that of hydronium ions under different pressure drops due to the lower molecular weight and diffusion activation energy of water molecules (20.25 kJ/mol). Hydronium ions formed stronger hydrogen bonds with sulfonic acid groups than water molecules, which resulted in a higher diffusion activation energy for hydronium ions (21.15 kJ/mol). The proton conductivity rose with the increase in pressure difference. Moreover, the transport diffusion coefficient of water molecules and hydronium ions were positively correlated with temperature. This is because the kinetic energy of molecules increased and the pore size of the Nafion membrane enlarged at high temperatures. In addition, the dynamics of the hydrogen bond between hydronium ions and sulfonic acid groups/water molecules were accelerated at elevated temperatures, which further promoted proton transfer.

Molecular Dynamics Study on the Diffusion Behavior of Water Molecules and the Dielectric Constant of Vegetable/Mineral Oil Blends.

Insulating oil plays a crucial role in internal insulation of oil-impregnated transformers. It has been demonstrated in a variety of experimental studies that mineral oil (MO) and vegetable oil (VO) can be blended in different ratios to improve insulation properties; however, the mechanisms underlying this phenomenon remain unclear. In this study, a molecular dynamics (MD) simulation approach was used to investigate diffusion of water molecules in VO/MO blends and dielectric constants of a mixture. The results show that the diffusion coefficient of water molecules is negatively correlated with the proportion of VO; thus, addition of VO helps to improve the insulation properties of a mixture. Due to introduction of strong polar functional groups, a decrease in the diffusion behavior of water molecules can be attributed to an increase in the interaction energy and formation of hydrogen bonds between water molecules and the mixed oil system. There is a direct correlation between the dielectric constant of a mixture and VO content; however, it is very sensitive to water content. The presence of strong polar water molecules or functional groups in a mixture leads to an increase in the dielectric constant, which results in a reduction in insulating properties. Accordingly, presence of polar groups plays an important role in determining the insulating properties of a mixture. To increase the insulation performance of a mixture, it is important to consider the diffusion-inhibiting and dielectric effects of the stronger polar groups in vegetable oil compared to those in mineral oil.

Deep Learning to Reveal the Distribution and Diffusion of Water Molecules in Fuel Cell Catalyst Layers

Water management in the catalyst layers (CLs) of proton-exchange membrane fuel cells is crucial for its commercialization and popularization. However, the high experimental or computational cost in obtaining water distribution and diffusion remains a bottleneck in the existing experimental methods and simulation algorithms, and further mechanistic exploration at the nanoscale is necessary. Herein, we integrate, for the first time, molecular dynamics simulation with our customized analysis framework based on a multiattribute point cloud dataset and an advanced deep learning network. This was achieved through our workflow that generates simulated transport data of water molecules in the CLs as the training and test dataset. Deep learning framework models the multibody solid-liquid system of CLs on a molecular scale and completes the mapping from the Pt/C substrate structure and Nafion aggregates to the density distribution and diffusion coefficient of water molecules. The prediction results are comprehensively analyzed and error evaluated, which reveals the highly anisotropic interaction landscape between 50,000 pairs of interacting nanoparticles and explains the structure and water transport property relationship in the hydrated Nafion film on the molecular scale. Compared to the conventional methods, the proposed deep learning framework shows computational cost efficiency, accuracy, and good visual display. Further, it has a generality potential to model macro- and microscopic mass transport in different components of fuel cells. Our framework is expected to make real-time predictions of the distribution and diffusion of water molecules in CLs as well as establish statistical significance in the structural optimization and design of CLs and other components of fuel cells.

Degradation of thermal stability and micromechanical properties of the C-S-H phase induced by ultra-confined water at elevated temperatures.

Water in the nanometer to micrometer-sized pores of calcium silicate hydrate (C-S-H) is essential for the binding process of cementitious materials. The quantity, location, and physical state of water in C-S-H pores under extreme conditions significantly influence the strength and durability of cementitious materials. The present study employed ReaxFF and molecular dynamics (MD) simulation to evaluate the effects of water ultra-confined in the nanopores on the structure, bonds, dynamics, and tensile mechanism of the C-S-H grains at elevated temperatures. The results indicate that the temperature elevation may interfere with the water molecule's hydrogen-bond network between the C-S-H grains, causing a notable nanometer-scale pore expansion. Simultaneously, the diffusion coefficient of water molecules confined in nanopores gradually increased, and their dynamic characteristics shifted from a glassy nature to free water. Additionally, high temperatures promoted hydrolysis reactions and the breakage of chemical bonds in the C-S-H framework, causing disintegration of the silicate skeleton and a decrease in the mechanical attributes of C-S-H. Moreover, the uniaxial tensile test at high temperatures revealed that the silicate chain groups in the C-S-H substrates underwent thermal curling. In contrast to interlayer-bound water, under the action of tension, water molecules in nanopores are viscous, forming water layers.

The selective heating effect of microwave irradiation on a binary mixture of water and polyethylene oxide: a molecular dynamics simulation approach.

In this study, we investigate the molecular mechanisms of a microwave-driven selective heating process by performing molecular dynamics simulations for three different systems including pure water, pure polyethylene oxide (PEO), and water-PEO mixed systems in the presence of a microwave with two different intensities of electric field such as 0.001 V Å-1 and 0.01 V Å-1 at a frequency of 100 GHz. First, from performing molecular dynamics simulations of CO and CO2 in the presence of the microwave, it is confirmed that the molecular dipole moment is responsible for the rotational motion induced by the oscillating electric field. Second, by analyzing the MD simulations of the pure water system, we discover that the dipole moment of water exhibits a time lag with respect to the microwave. During the heating process, however, the temperature, kinetic, and potential energies increase synchronously with the oscillating electric field of the microwave, showing that the heating of the water system is caused by the molecular reaction of water to the microwave. Comparing the water-PEO mixed system to the pure water and pure PEO systems, the water-PEO mixed system has a higher heating rate than the pure PEO system but a lower heating rate than the pure water system. Therefore, we conclude that heating the water-PEO mixed system is driven by water molecules selectively activated by microwave irradiation. We also calculate the diffusion coefficients of water molecules and PEO chains by describing their mean square displacements, demonstrating that the diffusion coefficients are increased in the presence of microwaves for both water and PEO in pure and mixed systems. Lastly, during the microwave heating process, the structures of the water-PEO mixed system are altered as a function of the intensity of electric field, which is mainly driven by the response of water molecules.

Effect of graphene on the properties of epoxy in hygrothermal environment by molecular dynamics method

<abstract> <p>The physical and mechanical properties of graphene-reinforced epoxy (epoxy/graphene) in hygrothermal environment need to be comprehensively understood. This is because it is necessary to predict the durability of epoxy/graphene when epoxy/graphene is used in an aggressive environment with high humidity and high temperature. Based on the molecular dynamics method, the influences of water content (2, 4 and 6%) and temperature (298,333 and 368 K) on the physical and tensile properties of epoxy/graphene were studied in this research. The results showed that after the addition of graphene, the free volume fraction of epoxy and the diffusion coefficient of water molecules in the epoxy decreased, and the density, tensile strength and deformation performance of epoxy increased. In the hygrothermal environment, the tensile strength degradation rate of epoxy/graphene was lower than that of pure epoxy. The failure mechanism and mechanical response of epoxy/graphene during the tensile process in the nanoscale were revealed. The research results provide a reference for the design and performance optimization of epoxy/graphene composites in a hygrothermal environment.</p> </abstract>

Diffusion behavior of water molecules in binary mixed vegetable oils under the synergistic effect of temperature and nano-TiO2

Temperature and water are two important factors affecting the insulating properties of power insulating oil. Meanwhile, nanoparticles have received attention from researchers as the latest improvement method for the electrical performance and insulation properties of insulating oil. Therefore, in this study, we constructed models of pure binary mixed vegetable insulating oils and mixed insulating oils modified with nano-TiO2. The diffusion behaviour of water in the binary mixed vegetable insulating oil under the synergistic effect of temperature and nanoparticles was investigated. Results indicate that the diffusion coefficient of water molecules in the nano-TiO2 modified vegetable insulating oil decreased up to 30.7 % compared to the unmodified vegetable insulating oil. With the introduction of nanoparticles, the free volume of the oil model is reduced by 18.23 % on average, and the space for water molecules to move is greatly reduced. The average interaction energy of oil and water molecules decreased by 9.53 %, and a large number of water molecules formed hydrogen bonds with O atoms on the nanoparticles. The nano-TiO2 particles have a negative electrostatic potential distributed on the surface and have a strong electrostatic attraction to the free H3O+ in the oil. Compared with pure oil, water molecules in modified oil need higher temperature and higher kinetic energy to get rid of hydrogen bond with nanoparticles. Therefore, the introduction of nanoparticles has largely reduced the influence of temperature on the diffusion of water molecules.