Dynamic behavior of surfactant molecules, sodium dodecyl sulfonate (SDSN), cetyl trimethyl ammonium bromide (CTAB) and triton X-100, and their micelles in water solution at various concentrations were studied by chemi...Dynamic behavior of surfactant molecules, sodium dodecyl sulfonate (SDSN), cetyl trimethyl ammonium bromide (CTAB) and triton X-100, and their micelles in water solution at various concentrations were studied by chemical shift, self diffusion coefficient (D) and nuclear magnetic resonance relaxation (T1 and T2) measurements. Experimental results show that there exist turning points at surfactant concentration (C) nearby the critical micelle concentration (cmc) for all of the above-mentioned parameters, which approach the constant values when C equals 5 to 10 times cmc. T1 and T2 measurements show that when C<cmc, Triton X-100 molecules exhibit fast isotropic motion in water solution. After micellization, the motion of hydrophobic chains is far away from the extreme narrowing condition, however, the long hydrophilic oxyethylene chains move relatively freely, although their T1 and T2 become shorter in comparison with those of the molecules in mono-molecular state. The behavior of the hydrophobic chains within the micellar core of SDSN and CTAB is similar to that of Triton X-100 to some extent.展开更多
A new equation of self-diffusion coefficients for real fluids is proposed over wide temperature and density ranges.The new equation is derived from the molecular dynamics simulation data of LJ model fluid in literatur...A new equation of self-diffusion coefficients for real fluids is proposed over wide temperature and density ranges.The new equation is derived from the molecular dynamics simulation data of LJ model fluid in literature,which could be applied to gas,liquid and supercritical fluid (0≤ ρ * ≤1.0,0.8≤ T *≤4.0) with AAD 4.95% .With a generalized expression for the LJ parameters of pure real fluids according to the corresponding state principle and critical properties,the proposed equation is extended to pure real substances with the prediction accuracy 18.83%.Correlated LJ parameters are also used for comparison and the total AAD is 3.43% for 19 pure substances and 1299 data points.The new self-diffusion equation could be used in process design and development.展开更多
We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with t...We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.展开更多
基金Project supported by the National Climbing Project
文摘Dynamic behavior of surfactant molecules, sodium dodecyl sulfonate (SDSN), cetyl trimethyl ammonium bromide (CTAB) and triton X-100, and their micelles in water solution at various concentrations were studied by chemical shift, self diffusion coefficient (D) and nuclear magnetic resonance relaxation (T1 and T2) measurements. Experimental results show that there exist turning points at surfactant concentration (C) nearby the critical micelle concentration (cmc) for all of the above-mentioned parameters, which approach the constant values when C equals 5 to 10 times cmc. T1 and T2 measurements show that when C<cmc, Triton X-100 molecules exhibit fast isotropic motion in water solution. After micellization, the motion of hydrophobic chains is far away from the extreme narrowing condition, however, the long hydrophilic oxyethylene chains move relatively freely, although their T1 and T2 become shorter in comparison with those of the molecules in mono-molecular state. The behavior of the hydrophobic chains within the micellar core of SDSN and CTAB is similar to that of Triton X-100 to some extent.
基金江苏省自然科学基金 (No .BK9712 4)国家杰出青年科学基金 (No .2 992 5 616)资助项目
文摘A new equation of self-diffusion coefficients for real fluids is proposed over wide temperature and density ranges.The new equation is derived from the molecular dynamics simulation data of LJ model fluid in literature,which could be applied to gas,liquid and supercritical fluid (0≤ ρ * ≤1.0,0.8≤ T *≤4.0) with AAD 4.95% .With a generalized expression for the LJ parameters of pure real fluids according to the corresponding state principle and critical properties,the proposed equation is extended to pure real substances with the prediction accuracy 18.83%.Correlated LJ parameters are also used for comparison and the total AAD is 3.43% for 19 pure substances and 1299 data points.The new self-diffusion equation could be used in process design and development.
基金supported by the National Natural Science Foundation of China (Grant No. 51076128)the National High Technology Research and Development Program of China (Grant No. 2009AA05Z107)
文摘We use non-equilibrium molecular dynamics simulations to calculate the self-diffusion coefficient, D, of a Lennard Jones fluid over a wide density and temperature range. The change in self-diffusion coefficient with temperature decreases by increasing density. For density ρ＊ = ρσ3 = 0.84 we observe a peak at the value of the self-diffusion coefficient and the critical temperature T＊ = kT/ε = 1.25. The value of the self-diffusion coefficient strongly depends on system size. The data of the self-diffusion coefficient are fitted to a simple analytic relation based on hydrodynamic arguments. This correction scales as N-α, where α is an adjustable parameter and N is the number of particles. It is observed that the values of a 〈 1 provide quite a good correction to the simulation data. The system size dependence is very strong for lower densities, but it is not as strong for higher densities. The self-diffusion coefficient calculated with non-equilibrium molecular dynamic simulations at different temperatures and densities is in good agreement with other calculations fronl the literature.
