The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original...The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original formula.In this work,the rationality of the SED relation and its variants is examined by performing molecular dynamics simulations with the Lewis–Wahnstrom model of ortho-terphenyl(OTP).The results indicate the original SED relation is valid for OTP but the three variants are all broken down.The inconsistency between the SED relation and its variants is analyzed from the heterogeneous dynamics,the adopted assumptions and approximations as well as the interactions among molecules.Therefore,care should be taken when employing the variants to judge the validity of the SED relation in supercooled liquids.展开更多
Variants based on the assumption of effective hydrodynamic radius being a constant are usually adopted to test the Stokes-Einstein(SE)relation.The rationality of the assumption is examined by performing molecular dyna...Variants based on the assumption of effective hydrodynamic radius being a constant are usually adopted to test the Stokes-Einstein(SE)relation.The rationality of the assumption is examined by performing molecular dynamics simulations with the truncated Lennard-Jones-like(TLJ)model,Kob-Andersen model and ortho-terphenyl(OTP)model.The results indicate the assumption is generally not established except for special case.The effective hydrodynamic radius is observed to increase with decreasing temperature for TLJ model but is decreased for Kob-Andersen and OTP model;and which is almost a constant for TLJ particle with enough rigidity.The variant of SE relation D~Th is invalid for the three models except for the TLJ particle with enough rigidity.We propose similar inconsistency may be also existed in other liquids and the assumption should be critically evaluated when adopted to test the SE relation.展开更多
The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time a...The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time and T is the temperature. In many glassforming liquids, the breakdown of SE relation often occurred when the dynamics of the liquids becomes glassy, and its origin is still debated among many scientists. Using molecular dynamics simulations and support-vector machine method, it is found that the scaling between diffusion and relaxation fails when the total population of solid-like clusters shrinks at the maximal rate with decreasing temperature, which implies a dramatic unification of clusters into an extensive dominant one occurs at the time of breakdown of the SE relation. Our data leads to an interpretation that the SE violation in metallic glass-forming liquids can be attributed to a specific change in the atomic structures.展开更多
The impact of ring polymer length N and the influence of interchain and intrachain interactions on the size and dynamic behaviors of ring polymers,including the structural relaxation time τ_(R) and self-diffusion coe...The impact of ring polymer length N and the influence of interchain and intrachain interactions on the size and dynamic behaviors of ring polymers,including the structural relaxation time τ_(R) and self-diffusion coefficient D,remain poorly understood at present due to a lack of systematic studies with relatively large N values.This work addressed this issue by applying dynamic Monte Carlo simulations with independently tuned interchain and intrachain interactions to investigate the size and dynamics of the ring melts with chain lengths over a wide range of 0.2N_(e)≤N≤80N_(e)(N_(e) is the entanglement length of corresponding linear chains)under different topological constraints,including all-crossing and intercrossing systems.We found that it was inappropriate to treat the unknotting constraint free energy of the ring chains in the melts as the free energy contributed by the excluded volume interactions of polymers in a good solvent.Scaling exponents of 2.5 and 1.5 reflecting the Ndependence of τ_(R) were obtained for long ring chains in non-crossing and intra-crossing systems,respectively,suggesting that the ring chains behaved as individual clusters and exhibited Zimm-like dynamics in intra-crossing systems.A single scaling exponent of-2 reflecting the Ndependence of D was obtained for ring chains in non-crossing and intra-crossing systems,indicating that the intrachain constraints affected only the value of D,and had little influence on the scaling relationship between D and N.Furthermore,the extended Stokes-Einstein relation broke down for the ring chains in the non-crossing and intra-crossing systems because the structural relaxation and translational diffusion were decoupled for the short ring systems,while both the translational diffusion and rotational relaxations,as well as diffusion at short and long time scales,were decoupled for long ring systems.展开更多
Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantl...Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantly from that in the bulk. Based on the simple quasicrystal model of liquid, analytical expressions of self-diffusion coefficient both in bulk and in slit nanopore are derived from the Stokes–Einstein equation and the modified Eyring's equation for viscosity. The local self-diffusion coefficient in different layers of liquid and the global self-diffusion coefficient in the slit nanopore are deduced from these expressions. The influences of confinement by pore walls,pore widths, liquid density, and temperature on the self-diffusion coefficient are investigated. The results indicate that the self-diffusion coefficient in nanopore increases with the pore width and approaches the bulk value as the pore width is sufficiently large. Similar to that in bulk state, the self-diffusion coefficient in nanopore decreases with the increase of density and the decrease of temperature, but these dependences are weaker than that in bulk state and become even weaker as the pore width decreases. This work provides a simple method to capture the physical behavior and to investigate the dynamic properties of liquid in nanopores.展开更多
Fractional Stokes–Einstein relation described by D ～（τ/T）~ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ =τ^（-1...Fractional Stokes–Einstein relation described by D ～（τ/T）~ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ =τ^（-1）. In this work, the Stokes–Einstein relation in TIP5 P water is examined at high temperatures within 400 K–800 K. Our results indicate that the fractional Stokes–Einstein relation is explicitly existent in TIP5P water at high temperatures, demonstrated by the two usually adopted variants of the Stokes–Einstein relation, D ～τ^（-1）τand D ～ T/τ, as well as by D ～ T/η, where η is the shear viscosity. Both D ～τ^（-1）τand D ～ T/τ are crossed at temperature Tx= 510 K. The D ～τ^（-1）τis in a fractional form as D ～ τ ξwith ξ =-2.09 for T ≤ Txand otherwise ξ =τ^（-1）.25. The D ～ T/τ is valid with ξ =τ^（-1）.01 for T ≤ Txbut in a fractional form for T Tx. The Stokes–Einstein relation D ～ T/η is satisfied below Tx = 620 K but in a fractional form above Tx. We propose that the breakdown of D ～ T/η may result from the system entering into the super critical region, the fractional forms of D ～τ^（-1）τand D ～ T/τ are due to the disruption of the hydration shell and the local tetrahedral structure as well as the increase of the shear viscosity.展开更多
基金supported by the National Natural Science Foundation of China (No. 12104502)the Natural Science Foundation of Sichuan Province (No. 2023YFG0308)
文摘The Stokes–Einstein–Debye(SED)relation is proposed to be broken down in supercooled liquids by many studies.However,conclusions are usually drawn by testing some variants of the SED relation rather than its original formula.In this work,the rationality of the SED relation and its variants is examined by performing molecular dynamics simulations with the Lewis–Wahnstrom model of ortho-terphenyl(OTP).The results indicate the original SED relation is valid for OTP but the three variants are all broken down.The inconsistency between the SED relation and its variants is analyzed from the heterogeneous dynamics,the adopted assumptions and approximations as well as the interactions among molecules.Therefore,care should be taken when employing the variants to judge the validity of the SED relation in supercooled liquids.
基金supported by the National Natural Science Foundation of China(No.12104502)the Science Foundation of Civil Aviation Flight University of China(No.J2021-054)
文摘Variants based on the assumption of effective hydrodynamic radius being a constant are usually adopted to test the Stokes-Einstein(SE)relation.The rationality of the assumption is examined by performing molecular dynamics simulations with the truncated Lennard-Jones-like(TLJ)model,Kob-Andersen model and ortho-terphenyl(OTP)model.The results indicate the assumption is generally not established except for special case.The effective hydrodynamic radius is observed to increase with decreasing temperature for TLJ model but is decreased for Kob-Andersen and OTP model;and which is almost a constant for TLJ particle with enough rigidity.The variant of SE relation D~Th is invalid for the three models except for the TLJ particle with enough rigidity.We propose similar inconsistency may be also existed in other liquids and the assumption should be critically evaluated when adopted to test the SE relation.
基金the National Natural Science Foundation of China(Grant Nos.11804027,and 11525520)the National Basic Research Program of China(Grant No.2015CB856801)the Fundamental Research Funds for the Central Universities(Grant No.2018NTST24).
文摘The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time and T is the temperature. In many glassforming liquids, the breakdown of SE relation often occurred when the dynamics of the liquids becomes glassy, and its origin is still debated among many scientists. Using molecular dynamics simulations and support-vector machine method, it is found that the scaling between diffusion and relaxation fails when the total population of solid-like clusters shrinks at the maximal rate with decreasing temperature, which implies a dramatic unification of clusters into an extensive dominant one occurs at the time of breakdown of the SE relation. Our data leads to an interpretation that the SE violation in metallic glass-forming liquids can be attributed to a specific change in the atomic structures.
基金the National Key R&D Program of China (No. 2020YFA0713601)the National Natural Science Foundation of China (Nos. 21790340 and 22073092)the Programs of Chinese Academy of Sciences (No. QYZDYSSW-SLH027)。
文摘The impact of ring polymer length N and the influence of interchain and intrachain interactions on the size and dynamic behaviors of ring polymers,including the structural relaxation time τ_(R) and self-diffusion coefficient D,remain poorly understood at present due to a lack of systematic studies with relatively large N values.This work addressed this issue by applying dynamic Monte Carlo simulations with independently tuned interchain and intrachain interactions to investigate the size and dynamics of the ring melts with chain lengths over a wide range of 0.2N_(e)≤N≤80N_(e)(N_(e) is the entanglement length of corresponding linear chains)under different topological constraints,including all-crossing and intercrossing systems.We found that it was inappropriate to treat the unknotting constraint free energy of the ring chains in the melts as the free energy contributed by the excluded volume interactions of polymers in a good solvent.Scaling exponents of 2.5 and 1.5 reflecting the Ndependence of τ_(R) were obtained for long ring chains in non-crossing and intra-crossing systems,respectively,suggesting that the ring chains behaved as individual clusters and exhibited Zimm-like dynamics in intra-crossing systems.A single scaling exponent of-2 reflecting the Ndependence of D was obtained for ring chains in non-crossing and intra-crossing systems,indicating that the intrachain constraints affected only the value of D,and had little influence on the scaling relationship between D and N.Furthermore,the extended Stokes-Einstein relation broke down for the ring chains in the non-crossing and intra-crossing systems because the structural relaxation and translational diffusion were decoupled for the short ring systems,while both the translational diffusion and rotational relaxations,as well as diffusion at short and long time scales,were decoupled for long ring systems.
基金Supported by Guangdong Science and Technology Project(2012B050600012)
文摘Dynamical properties of liquid in nano-channels attract much interest because of their applications in engineering and biological systems. The transfer behavior of liquid confined within nanopores differs significantly from that in the bulk. Based on the simple quasicrystal model of liquid, analytical expressions of self-diffusion coefficient both in bulk and in slit nanopore are derived from the Stokes–Einstein equation and the modified Eyring's equation for viscosity. The local self-diffusion coefficient in different layers of liquid and the global self-diffusion coefficient in the slit nanopore are deduced from these expressions. The influences of confinement by pore walls,pore widths, liquid density, and temperature on the self-diffusion coefficient are investigated. The results indicate that the self-diffusion coefficient in nanopore increases with the pore width and approaches the bulk value as the pore width is sufficiently large. Similar to that in bulk state, the self-diffusion coefficient in nanopore decreases with the increase of density and the decrease of temperature, but these dependences are weaker than that in bulk state and become even weaker as the pore width decreases. This work provides a simple method to capture the physical behavior and to investigate the dynamic properties of liquid in nanopores.
基金supported by the National Natural Science Foundation of China(Grant No.2153200)the China Postdoctoral Science Foundation(Grant No.2016M602712)
文摘Fractional Stokes–Einstein relation described by D ～（τ/T）~ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ =τ^（-1）. In this work, the Stokes–Einstein relation in TIP5 P water is examined at high temperatures within 400 K–800 K. Our results indicate that the fractional Stokes–Einstein relation is explicitly existent in TIP5P water at high temperatures, demonstrated by the two usually adopted variants of the Stokes–Einstein relation, D ～τ^（-1）τand D ～ T/τ, as well as by D ～ T/η, where η is the shear viscosity. Both D ～τ^（-1）τand D ～ T/τ are crossed at temperature Tx= 510 K. The D ～τ^（-1）τis in a fractional form as D ～ τ ξwith ξ =-2.09 for T ≤ Txand otherwise ξ =τ^（-1）.25. The D ～ T/τ is valid with ξ =τ^（-1）.01 for T ≤ Txbut in a fractional form for T Tx. The Stokes–Einstein relation D ～ T/η is satisfied below Tx = 620 K but in a fractional form above Tx. We propose that the breakdown of D ～ T/η may result from the system entering into the super critical region, the fractional forms of D ～τ^（-1）τand D ～ T/τ are due to the disruption of the hydration shell and the local tetrahedral structure as well as the increase of the shear viscosity.
