Colloidal polymers with tunable chain stiffness have been successfully assembled in experiments recently.Similar to molecular polymers,chain stiffness is an important feature which can distinctly affect the dynamical ...Colloidal polymers with tunable chain stiffness have been successfully assembled in experiments recently.Similar to molecular polymers,chain stiffness is an important feature which can distinctly affect the dynamical behaviors of colloidal polymers.Hence,we model colloidal polymers with controlled chain stiffness and study the effect of chain stiffness on glassy behaviors.For stiff chains,there are long-ranged periodic intrachain correlations besides two incompatible local length scales,i.e.,monomer size and bond length.The mean square displacement of monomers exhibits sub-diffusion at intermediate time/length scale and the sub-diffusive exponent increases with chain stiffness.The data of localization length of stiff polymers versus rescaled volume fraction for different monomer sizes can gather close to an exponential curve and decay slower than those of flexible polymers.The increase of chain stiffness linearly increases the activation energy of the colloidal-polymer system and thus makes the colloidal polymers vitrify at lower volume fraction.Static and dynamic equivalences between stiff colloidal polymers of different monomer sizes have been checked.展开更多
Three-dimensional (3D) Fick's diffusion equation and fractional diffusion equation are solved for different reflecting boundaries. We use the continuous time random walk model (CTRW) to investigate the time-avera...Three-dimensional (3D) Fick's diffusion equation and fractional diffusion equation are solved for different reflecting boundaries. We use the continuous time random walk model (CTRW) to investigate the time-averaged mean square dis- placement (MSD) of a 3D single particle trajectory. Theoretical results show that the ensemble average of the time-averaged MSD can be expressed analytically by a Mittag-Leffler function. Our new expression is in agreement with previous formu- las in two limiting cases: (^-δ2) ~ △1 in short lag time and (^-δ2} ~ △1 -α in long lag time. We also simulate the experimental data of mRNA diffusion in living E. coli using a 3D CTRW model under confined and crowded conditions. The simulation results are well consistent with experimental results. The calculations of power spectral density (PSD) further indicate the subdiffsive behavior of an individual trajectory.展开更多
Under different temperatures and concentrations, the diffusion of Vitamin C (VC) in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein eq...Under different temperatures and concentrations, the diffusion of Vitamin C (VC) in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein equation. The influences of temperature, concentration, and simulation time on the diffusion coefficient were discussed. The results showed that at higher temperature and lower concentration the normal diffusions appear relatively late, but the linear range of mean square displacement curves continues longer than that at lower temperature and higher concentration. At the same temperature, the normal diffusion time increases and the diffusion coefficient decreases as the simulation concentration increases. These simulation results are in good agreement with experiments. Analyses of the pair correlation functions of the simulation systems showed that hydrogen bonds are mainly formed be- tween the hydrogen atoms of VC molecules and oxygen atoms of H20 molecules, rather than between the O atoms of VC molecules and H atoms of H20 molecules. The diffusion coefficient is higher as the interaction between water molecules and VC molecules is stronger when VC concentration is lower. The water in the model systems affects the diffusion of VC molecules by the short-range repulsion of O(H20)-O(H20) pairs and the non-bond interaction of H(H20)-H(H20) pairs. The short-range repulsion of O(H20)-O(H20) pairs is greater when VC concentration is higher, the diffusion of VC is weaker. The greater the non-bond interaction of H(H20)-H(H20) pairs is, the higher the VC diffusion is. It is expected that this study can provide a theoretical direction for the experiments on the mass transfer of VC in water solution.展开更多
The modified embedded atom method(MEAM)with the universal form of embedding function and a modified energy term along with the pair potential has been employed to determine the potentials for alkali metals:Na,K,by fit...The modified embedded atom method(MEAM)with the universal form of embedding function and a modified energy term along with the pair potential has been employed to determine the potentials for alkali metals:Na,K,by fitting to the Cauchy pressure(C_(12)−C_(44))/2,shear constants Gv=(C_(11)−C_(12)+3C_(44))/5 and C_(44),the cohesive energy and the vacancy formation energy.The obtained potentials are used to calculate the phonon dispersions of these metals.Using these calculated phonons we evaluate the local density of states of neighbours of vacancy using Green’s function method.The local density of states of neighbours of vacancy has been used to calculate mean square displacements of these atoms and formation entropy of vacancy.The calculated mean square displacements of both 1st and 2nd neighbours of vacancy are found to be lower than that of host atom.The calculated phonon dispersions agree well with the experimental phonon dispersion curves and the calculated results of vacancy formation entropy compare well with the other available results.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11804085 and 11847115)the Doctoral Foundation of Heze University(Grant No.XY18BS13).
文摘Colloidal polymers with tunable chain stiffness have been successfully assembled in experiments recently.Similar to molecular polymers,chain stiffness is an important feature which can distinctly affect the dynamical behaviors of colloidal polymers.Hence,we model colloidal polymers with controlled chain stiffness and study the effect of chain stiffness on glassy behaviors.For stiff chains,there are long-ranged periodic intrachain correlations besides two incompatible local length scales,i.e.,monomer size and bond length.The mean square displacement of monomers exhibits sub-diffusion at intermediate time/length scale and the sub-diffusive exponent increases with chain stiffness.The data of localization length of stiff polymers versus rescaled volume fraction for different monomer sizes can gather close to an exponential curve and decay slower than those of flexible polymers.The increase of chain stiffness linearly increases the activation energy of the colloidal-polymer system and thus makes the colloidal polymers vitrify at lower volume fraction.Static and dynamic equivalences between stiff colloidal polymers of different monomer sizes have been checked.
基金supported by the National Natural Science Foundation of China(Grant No.21153002)the Fundamental Research Funds for the Central Universities of China(Grant No.2013zzts151)
文摘Three-dimensional (3D) Fick's diffusion equation and fractional diffusion equation are solved for different reflecting boundaries. We use the continuous time random walk model (CTRW) to investigate the time-averaged mean square dis- placement (MSD) of a 3D single particle trajectory. Theoretical results show that the ensemble average of the time-averaged MSD can be expressed analytically by a Mittag-Leffler function. Our new expression is in agreement with previous formu- las in two limiting cases: (^-δ2) ~ △1 in short lag time and (^-δ2} ~ △1 -α in long lag time. We also simulate the experimental data of mRNA diffusion in living E. coli using a 3D CTRW model under confined and crowded conditions. The simulation results are well consistent with experimental results. The calculations of power spectral density (PSD) further indicate the subdiffsive behavior of an individual trajectory.
基金This work was financially supported by open projectfrom the Key Laboratory of Genetic Breeding and Aquaculture Biology of Freshwater Fisher, Ministry of Agriculture, China (No. BZ2007-06) and the Natural Science Foundation of Jiangsu province, Higher Educa- tion Institution of China (No. 08KJD240003).
文摘Under different temperatures and concentrations, the diffusion of Vitamin C (VC) in water solution was exam- ined by molecular dynamics simulation. The diffusion coefficients were calculated based on the Einstein equation. The influences of temperature, concentration, and simulation time on the diffusion coefficient were discussed. The results showed that at higher temperature and lower concentration the normal diffusions appear relatively late, but the linear range of mean square displacement curves continues longer than that at lower temperature and higher concentration. At the same temperature, the normal diffusion time increases and the diffusion coefficient decreases as the simulation concentration increases. These simulation results are in good agreement with experiments. Analyses of the pair correlation functions of the simulation systems showed that hydrogen bonds are mainly formed be- tween the hydrogen atoms of VC molecules and oxygen atoms of H20 molecules, rather than between the O atoms of VC molecules and H atoms of H20 molecules. The diffusion coefficient is higher as the interaction between water molecules and VC molecules is stronger when VC concentration is lower. The water in the model systems affects the diffusion of VC molecules by the short-range repulsion of O(H20)-O(H20) pairs and the non-bond interaction of H(H20)-H(H20) pairs. The short-range repulsion of O(H20)-O(H20) pairs is greater when VC concentration is higher, the diffusion of VC is weaker. The greater the non-bond interaction of H(H20)-H(H20) pairs is, the higher the VC diffusion is. It is expected that this study can provide a theoretical direction for the experiments on the mass transfer of VC in water solution.
文摘The modified embedded atom method(MEAM)with the universal form of embedding function and a modified energy term along with the pair potential has been employed to determine the potentials for alkali metals:Na,K,by fitting to the Cauchy pressure(C_(12)−C_(44))/2,shear constants Gv=(C_(11)−C_(12)+3C_(44))/5 and C_(44),the cohesive energy and the vacancy formation energy.The obtained potentials are used to calculate the phonon dispersions of these metals.Using these calculated phonons we evaluate the local density of states of neighbours of vacancy using Green’s function method.The local density of states of neighbours of vacancy has been used to calculate mean square displacements of these atoms and formation entropy of vacancy.The calculated mean square displacements of both 1st and 2nd neighbours of vacancy are found to be lower than that of host atom.The calculated phonon dispersions agree well with the experimental phonon dispersion curves and the calculated results of vacancy formation entropy compare well with the other available results.