The grain boundary is an interface and the surface tension is one of its important thermodynamic properties. In this paper, the surface tension of the Σ9 grain boundary for α-Fe at various temperatures and pressures...The grain boundary is an interface and the surface tension is one of its important thermodynamic properties. In this paper, the surface tension of the Σ9 grain boundary for α-Fe at various temperatures and pressures is calculated by means of Computer Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It. is shown that the contribution of entropy to surface tension of grain boundary can be ignored.展开更多
For the determination of surface tension of liquid droplets by molecular dynamics simulations, the most timeconsuming part is the calculation of pressure tensor in the transition layer, which makes it difficult to enh...For the determination of surface tension of liquid droplets by molecular dynamics simulations, the most timeconsuming part is the calculation of pressure tensor in the transition layer, which makes it difficult to enhance the precision of the computation. A new method for the calculation of surface tension of liquid droplets to reduce the calculation quantity of pressure tensor in transition layer to the minimum is proposed in this paper. Two thousand particles are taken as example to show how to carry out our scheme.展开更多
A molecular dynamics simulation model is established based on the well-known Lennard-Jones 12-6 potential function to determine the surface tension of a Lennard-Jones liquid-vapor interface. The simulation is carried ...A molecular dynamics simulation model is established based on the well-known Lennard-Jones 12-6 potential function to determine the surface tension of a Lennard-Jones liquid-vapor interface. The simulation is carried out with argon as the working fluid of a given molecular number at different temperature and different truncated radius. It is found that the surface tension of a Lennard-Jones fluid is likely to be bigger for a bigger truncated radius, and tends to be constant after the truncated radius increased to a certain value. It is also found that the surface tension becomes smaller as the temperature increases.展开更多
In view of the continued disputes on the fundamental question of whether the surface tension of a vapour bubble in liquid argon increases, or decreases, or remains unchanged with the increase of curvature radius, a cy...In view of the continued disputes on the fundamental question of whether the surface tension of a vapour bubble in liquid argon increases, or decreases, or remains unchanged with the increase of curvature radius, a cylindrical vapour bubble of argon is studied by molecular dynamics simulation in this paper instead of spherical vapour bubble so as to reduce the statistical error. So far, the surface tension of the cylindrical vapour bubble has not been studied by molecular dynamics simulation in the literature. Our results show that the surface tension decreases with radius increasing. By fitting the Tolman equation with our data, the Tolman length σ = -0.6225 sigma is given under cut-off radius 2.5σ, where σ = 0.3405 nm is the diameter of an argon atom. The Tolman length of Ar being negative is affirmed and the Tolman length of Ar being approximately zero given in the literature is negated, and it is pointed out that this error is attributed to the application of the inapplicable empirical equation of state and the neglect of the difference between surface tension and an equimolar surface.展开更多
In 1949, Tolman found the relation between the surface tension and Tolman length, which determines the dimensional effect of the surface tension. Tolman length is the difference between the equimolar surface and the s...In 1949, Tolman found the relation between the surface tension and Tolman length, which determines the dimensional effect of the surface tension. Tolman length is the difference between the equimolar surface and the surface of tension. In recent years, the magnitude, expression, and sign of the Tolman length remain an open question. An incompressible and homogeneous liquid droplet model is proposed and the approximate expression and sign for Tolman length are derived in this paper. We obtain the relation between Tolman length and the radius of the surface of tension(R_(s)) and found that they increase with the Rs decreasing. The Tolman length of plane surface tends to zero. Taking argon for example, molecular dynamics simulation is carried out by using the Lennard–Jones(LJ) potential between atoms at a temperature of 90 K. Five simulated systems are used, with numbers of argon atoms being 10140, 10935, 11760, 13500, and 15360, respectively. By methods of theoretical study and molecular dynamics simulation, we find that the calculated value of Tolman length is more than zero, and it decreases as the size is increased among the whole size range. The value of surface tension increases with the radius of the surface of tension increasing, which is consistent with Tolman’s theory. These conclusions are significant for studying the size dependence of the surface tension.展开更多
To investigate the microscopicmechanism underlying the influence of surface-chemical gradient on heat andmass recovery,a molecular dynamicsmodel including droplet condensation and transport process has been developed ...To investigate the microscopicmechanism underlying the influence of surface-chemical gradient on heat andmass recovery,a molecular dynamicsmodel including droplet condensation and transport process has been developed to examine heat and mass recovery performance.This work aimed at identify optimal conditions for enhancing heat and mass recovery through the combination of wettability gradient and nanopore transport.For comprehensive analysis,the structure in the simulation was categorized into three distinct groups:a homogeneous structure,a small wettability gradient,and a large wettability gradient.The homogeneous surface demonstrated low efficiency in heat and mass transfer,as evidenced by filmwise condensation.In contrast,the surface with a small wettability gradient experienced a transition from dropwise condensation to filmwise condensation,resulting in a gradual decrease in the efficiency of vapor heat and mass transfer.Only a large wettability gradient could achieve periodic and efficient dropwise condensation heat and mass transfer which was attributed to the rapid droplet coalescence and transport to the nanopore after condensing on the cold surface.展开更多
In 1805, Thomas Young was the first to propose an equation(Young's equation) to predict the value of the equilibrium contact angle of a liquid on a solid. On the basis of our predecessors, we further clarify that ...In 1805, Thomas Young was the first to propose an equation(Young's equation) to predict the value of the equilibrium contact angle of a liquid on a solid. On the basis of our predecessors, we further clarify that the contact angle in Young's equation refers to the super-nano contact angle. Whether the equation is applicable to nanoscale systems remains an open question. Zhu et al. [College Phys. 4 7(1985)] obtained the most simple and convenient approximate formula, known as the Zhu–Qian approximate formula of Young's equation. Here, using molecular dynamics simulation, we test its applicability for nanodrops. Molecular dynamics simulations are performed on argon liquid cylinders placed on a solid surface under a temperature of 90 K, using Lennard–Jones potentials for the interaction between liquid molecules and between a liquid molecule and a solid molecule with the variable coefficient of strength a. Eight values of a between 0.650 and 0.825 are used. By comparison of the super-nano contact angles obtained from molecular dynamics simulation and the Zhu–Qian approximate formula of Young's equation, we find that it is qualitatively applicable for nanoscale systems.展开更多
Molecular dynamics simulations were performed to study the surface properties of water in a temperature range from 228 to 293 K by using the extended simple point charge (SPC/E) and four-site TIP4P potentials. The cal...Molecular dynamics simulations were performed to study the surface properties of water in a temperature range from 228 to 293 K by using the extended simple point charge (SPC/E) and four-site TIP4P potentials. The calculated surface tension increases with the decrease of temperature, and moreover the slopes of the surface tension-temperature curves show a weak rise below 273 K, whereas no obvious anomalies appear near 228 K, which accords with the previous experiments. Compared with the measured values, the SPC/E potential shows a good agreement, and the TIP4P potential underestimates the surface tension. The main reason for that may be the reasonable description of the surface structure of supercooled water for the SPC/E. When simulating the orientational distributions of water molecules near the surface, the SPC/E potential produces higher ordering and larger surface potentials than the TIP4P potential.展开更多
The thermodynamic property of asphalt binder is changed by the addition of crumb rubber,which in turn influences the self-healing property as well as the cohesion and adhesion within the asphalt-aggregate system.This ...The thermodynamic property of asphalt binder is changed by the addition of crumb rubber,which in turn influences the self-healing property as well as the cohesion and adhesion within the asphalt-aggregate system.This study investigated the self-healing and interface properties of crumb rubber modified asphalt(CRMA)using thermodynamic parameters based on the molecular simulation approach.The molecular models of CRMA were built with representative structures of the virgin asphalt and the crumb rubber.The aggregate was represented by SiO2 and Al2O3 crystals.The selfhealing capability was evaluated with the thermodynamic parameter wetting time,work of cohesion and diffusivity.The interface properties were evaluated by characterizing the adhesion capability,the debonding potential and the moisture susceptibility of the asphalt-aggregate interface.The self-healing capability of CRMA is found to decrease as the rubber content increases.The asphalt-Al2O3 interface with higher rubber content has stronger adhesion and moisture stability.But the influence of crumb rubber on the interfacial properties of asphalt-SiO2 interface has no statistical significance.Comparing with the interfacial properties of the asphalt-SiO2 interface,the asphalt-Al2O3 interface is found to have a stronger adhesion but a worse moisture susceptibility for its enormous thermodynamic potential for water to displace the asphalt binder.展开更多
Molecular dynamics simulations on the interface between liquid water and liquid n-alkane (including octane, nonane, decane, undecane and dodecane) have been performed with the purpose to study the interfacial properti...Molecular dynamics simulations on the interface between liquid water and liquid n-alkane (including octane, nonane, decane, undecane and dodecane) have been performed with the purpose to study the interfacial properties: (Ⅰ) density profile; (Ⅱ) molecular orientation; (Ⅲ) interfacial tension and the temperature effect on the interfacial tension. Simulation results show that at the interface the structures of both water and n-alkane are different from those in the bulk. Water has an orientational preference due to the number of hydrogen bonds per molecule maximized. N-alkane has a more lateral orientation with respect to the interface in order to be in close contact with water. The calculated individual phase bulk density and interfacial tension of water/n-alkane systems are in good agreement with the corresponding experimental ones.展开更多
There are a few studies on the use of ferro-nanofluids for enhanced oil recovery,despite their magnetic properties;hence,it is needed to study the adsorption of iron oxide(Fe2 O3 and Fe3 O4) nanoparticles(NPs) on rock...There are a few studies on the use of ferro-nanofluids for enhanced oil recovery,despite their magnetic properties;hence,it is needed to study the adsorption of iron oxide(Fe2 O3 and Fe3 O4) nanoparticles(NPs) on rock surfaces.This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface.Molecular dynamics simulation was used to determine the interfacial energy(strength) and adsorption of Fe2 O3 and Fe3 O4 nanofluids infused in reservoir sandstones.Fourier transform infrared spectroscopy and X-ray photon spectroscopy(XPS) were used to monitor interaction of silicate species with Fe2 O3 and Fe3 O4.The spectral changes show the variation of dominating silicate anions in the solution.Also,the XPS peaks for Si,C and Fe at 190,285 and 700 eV,respectively,are less distinct in the spectra of sandstone aged in the Fe3 O4 nanofluid,suggesting the intense adsorption of the Fe3 O4 with the crude oil.The measured IFT for brine/oil,Fe2 O3/oil and Fe3 O4/oil are 40,36.17 and 31 mN/m,respectively.Fe3 O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2 O3,due to their larger number of active surface sites and saturation magnetization,which accounts for the effectiveness of Fe3 O4 in reducing IFT.展开更多
For the diffusion-controlled adsorption, the expression of dynamic surface adsorption P(t) was ob- tained by solving the diffusion equation. Two cases, i.e. the short and long time limits, were mainly discussed in t...For the diffusion-controlled adsorption, the expression of dynamic surface adsorption P(t) was ob- tained by solving the diffusion equation. Two cases, i.e. the short and long time limits, were mainly discussed in this paper. From the measured dynamic surface tension of aqueous surfactant sodium dodecyl sulfate (SDS) solutions at 25 ℃, the adsorption kinetics of SDS at air/solution interface was studied. It was proved that for both of the short and long time limits, the adsorption process of SDS was controlled by diffusion.展开更多
基金The project supported by the National Natural Science Foundation of Chinathe Science Foundation of Chinese Academy of Sciences.
文摘The grain boundary is an interface and the surface tension is one of its important thermodynamic properties. In this paper, the surface tension of the Σ9 grain boundary for α-Fe at various temperatures and pressures is calculated by means of Computer Molecular Dynamics (CMD). The results agree satisfactorily with the experimental data. It. is shown that the contribution of entropy to surface tension of grain boundary can be ignored.
基金Project supported by the National Natural Science Foundation of China(Grant No.10772189)the Knowledge Innovation Program of Chinese Academy of Sciences
文摘For the determination of surface tension of liquid droplets by molecular dynamics simulations, the most timeconsuming part is the calculation of pressure tensor in the transition layer, which makes it difficult to enhance the precision of the computation. A new method for the calculation of surface tension of liquid droplets to reduce the calculation quantity of pressure tensor in transition layer to the minimum is proposed in this paper. Two thousand particles are taken as example to show how to carry out our scheme.
基金Funded by the National Natural Science Foundation of China (No.50076048)
文摘A molecular dynamics simulation model is established based on the well-known Lennard-Jones 12-6 potential function to determine the surface tension of a Lennard-Jones liquid-vapor interface. The simulation is carried out with argon as the working fluid of a given molecular number at different temperature and different truncated radius. It is found that the surface tension of a Lennard-Jones fluid is likely to be bigger for a bigger truncated radius, and tends to be constant after the truncated radius increased to a certain value. It is also found that the surface tension becomes smaller as the temperature increases.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11072242)
文摘In view of the continued disputes on the fundamental question of whether the surface tension of a vapour bubble in liquid argon increases, or decreases, or remains unchanged with the increase of curvature radius, a cylindrical vapour bubble of argon is studied by molecular dynamics simulation in this paper instead of spherical vapour bubble so as to reduce the statistical error. So far, the surface tension of the cylindrical vapour bubble has not been studied by molecular dynamics simulation in the literature. Our results show that the surface tension decreases with radius increasing. By fitting the Tolman equation with our data, the Tolman length σ = -0.6225 sigma is given under cut-off radius 2.5σ, where σ = 0.3405 nm is the diameter of an argon atom. The Tolman length of Ar being negative is affirmed and the Tolman length of Ar being approximately zero given in the literature is negated, and it is pointed out that this error is attributed to the application of the inapplicable empirical equation of state and the neglect of the difference between surface tension and an equimolar surface.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0700500)the Scientific Research and Innovation Team of Cangzhou Normal University,China(Grant No.cxtdl1907)+2 种基金the Key Scientific Study Program of Hebei Provincial Higher Education Institution,China(Grant No.ZD2020410)the Cangzhou Natural Science Foundation,China(Grant No.197000001)the General Scientific Research Fund Project of Cangzhou Normal University,China(Grant No.xnjjl1906)。
文摘In 1949, Tolman found the relation between the surface tension and Tolman length, which determines the dimensional effect of the surface tension. Tolman length is the difference between the equimolar surface and the surface of tension. In recent years, the magnitude, expression, and sign of the Tolman length remain an open question. An incompressible and homogeneous liquid droplet model is proposed and the approximate expression and sign for Tolman length are derived in this paper. We obtain the relation between Tolman length and the radius of the surface of tension(R_(s)) and found that they increase with the Rs decreasing. The Tolman length of plane surface tends to zero. Taking argon for example, molecular dynamics simulation is carried out by using the Lennard–Jones(LJ) potential between atoms at a temperature of 90 K. Five simulated systems are used, with numbers of argon atoms being 10140, 10935, 11760, 13500, and 15360, respectively. By methods of theoretical study and molecular dynamics simulation, we find that the calculated value of Tolman length is more than zero, and it decreases as the size is increased among the whole size range. The value of surface tension increases with the radius of the surface of tension increasing, which is consistent with Tolman’s theory. These conclusions are significant for studying the size dependence of the surface tension.
基金supported by the National Natural Science Foundation of China(No.52206093)the University Outstanding Youth Fund Project of Anhui Province(Nos.2022AH020028 and 2022AH030037)+2 种基金the Natural Science Foundation of Anhui Province(Nos.1908085QF292 and 2308085ME173)Anhui Province Outstanding Young Talents Support Program(No.gxyqZD2022058)Guangdong Basic and Applied Basic Research Foundation(Nos.2024A1515011379 and 2023A1515110613).
文摘To investigate the microscopicmechanism underlying the influence of surface-chemical gradient on heat andmass recovery,a molecular dynamicsmodel including droplet condensation and transport process has been developed to examine heat and mass recovery performance.This work aimed at identify optimal conditions for enhancing heat and mass recovery through the combination of wettability gradient and nanopore transport.For comprehensive analysis,the structure in the simulation was categorized into three distinct groups:a homogeneous structure,a small wettability gradient,and a large wettability gradient.The homogeneous surface demonstrated low efficiency in heat and mass transfer,as evidenced by filmwise condensation.In contrast,the surface with a small wettability gradient experienced a transition from dropwise condensation to filmwise condensation,resulting in a gradual decrease in the efficiency of vapor heat and mass transfer.Only a large wettability gradient could achieve periodic and efficient dropwise condensation heat and mass transfer which was attributed to the rapid droplet coalescence and transport to the nanopore after condensing on the cold surface.
基金Project supported by the National Natural Science Foundation of China(Grant No.11072242)the Key Scientific Studies Program of Hebei Province Higher Education Institute,China(Grant No.ZD2018301)Cangzhou National Science Foundation,China(Grant No.177000001)
文摘In 1805, Thomas Young was the first to propose an equation(Young's equation) to predict the value of the equilibrium contact angle of a liquid on a solid. On the basis of our predecessors, we further clarify that the contact angle in Young's equation refers to the super-nano contact angle. Whether the equation is applicable to nanoscale systems remains an open question. Zhu et al. [College Phys. 4 7(1985)] obtained the most simple and convenient approximate formula, known as the Zhu–Qian approximate formula of Young's equation. Here, using molecular dynamics simulation, we test its applicability for nanodrops. Molecular dynamics simulations are performed on argon liquid cylinders placed on a solid surface under a temperature of 90 K, using Lennard–Jones potentials for the interaction between liquid molecules and between a liquid molecule and a solid molecule with the variable coefficient of strength a. Eight values of a between 0.650 and 0.825 are used. By comparison of the super-nano contact angles obtained from molecular dynamics simulation and the Zhu–Qian approximate formula of Young's equation, we find that it is qualitatively applicable for nanoscale systems.
文摘Molecular dynamics simulations were performed to study the surface properties of water in a temperature range from 228 to 293 K by using the extended simple point charge (SPC/E) and four-site TIP4P potentials. The calculated surface tension increases with the decrease of temperature, and moreover the slopes of the surface tension-temperature curves show a weak rise below 273 K, whereas no obvious anomalies appear near 228 K, which accords with the previous experiments. Compared with the measured values, the SPC/E potential shows a good agreement, and the TIP4P potential underestimates the surface tension. The main reason for that may be the reasonable description of the surface structure of supercooled water for the SPC/E. When simulating the orientational distributions of water molecules near the surface, the SPC/E potential produces higher ordering and larger surface potentials than the TIP4P potential.
基金supported by the Special Fund for Basic Scientific Research of Central College of Chang’an University(Nos.300102218405,300102218413,and 310821153502)the Department of Science&Technology of Shaanxi Province(Nos.2016ZDJC-24 and 2017KCT-13).
文摘The thermodynamic property of asphalt binder is changed by the addition of crumb rubber,which in turn influences the self-healing property as well as the cohesion and adhesion within the asphalt-aggregate system.This study investigated the self-healing and interface properties of crumb rubber modified asphalt(CRMA)using thermodynamic parameters based on the molecular simulation approach.The molecular models of CRMA were built with representative structures of the virgin asphalt and the crumb rubber.The aggregate was represented by SiO2 and Al2O3 crystals.The selfhealing capability was evaluated with the thermodynamic parameter wetting time,work of cohesion and diffusivity.The interface properties were evaluated by characterizing the adhesion capability,the debonding potential and the moisture susceptibility of the asphalt-aggregate interface.The self-healing capability of CRMA is found to decrease as the rubber content increases.The asphalt-Al2O3 interface with higher rubber content has stronger adhesion and moisture stability.But the influence of crumb rubber on the interfacial properties of asphalt-SiO2 interface has no statistical significance.Comparing with the interfacial properties of the asphalt-SiO2 interface,the asphalt-Al2O3 interface is found to have a stronger adhesion but a worse moisture susceptibility for its enormous thermodynamic potential for water to displace the asphalt binder.
文摘Molecular dynamics simulations on the interface between liquid water and liquid n-alkane (including octane, nonane, decane, undecane and dodecane) have been performed with the purpose to study the interfacial properties: (Ⅰ) density profile; (Ⅱ) molecular orientation; (Ⅲ) interfacial tension and the temperature effect on the interfacial tension. Simulation results show that at the interface the structures of both water and n-alkane are different from those in the bulk. Water has an orientational preference due to the number of hydrogen bonds per molecule maximized. N-alkane has a more lateral orientation with respect to the interface in order to be in close contact with water. The calculated individual phase bulk density and interfacial tension of water/n-alkane systems are in good agreement with the corresponding experimental ones.
文摘There are a few studies on the use of ferro-nanofluids for enhanced oil recovery,despite their magnetic properties;hence,it is needed to study the adsorption of iron oxide(Fe2 O3 and Fe3 O4) nanoparticles(NPs) on rock surfaces.This is important as the colloidal transport of NPs through the reservoir is subject to particle adsorption on the rock surface.Molecular dynamics simulation was used to determine the interfacial energy(strength) and adsorption of Fe2 O3 and Fe3 O4 nanofluids infused in reservoir sandstones.Fourier transform infrared spectroscopy and X-ray photon spectroscopy(XPS) were used to monitor interaction of silicate species with Fe2 O3 and Fe3 O4.The spectral changes show the variation of dominating silicate anions in the solution.Also,the XPS peaks for Si,C and Fe at 190,285 and 700 eV,respectively,are less distinct in the spectra of sandstone aged in the Fe3 O4 nanofluid,suggesting the intense adsorption of the Fe3 O4 with the crude oil.The measured IFT for brine/oil,Fe2 O3/oil and Fe3 O4/oil are 40,36.17 and 31 mN/m,respectively.Fe3 O4 infused with reservoir sandstone exhibits a higher silicate sorption capacity than Fe2 O3,due to their larger number of active surface sites and saturation magnetization,which accounts for the effectiveness of Fe3 O4 in reducing IFT.
文摘For the diffusion-controlled adsorption, the expression of dynamic surface adsorption P(t) was ob- tained by solving the diffusion equation. Two cases, i.e. the short and long time limits, were mainly discussed in this paper. From the measured dynamic surface tension of aqueous surfactant sodium dodecyl sulfate (SDS) solutions at 25 ℃, the adsorption kinetics of SDS at air/solution interface was studied. It was proved that for both of the short and long time limits, the adsorption process of SDS was controlled by diffusion.