浓度对NaCl水溶液影响的分子动力学模拟

采用分子动力学(MD)模拟方法对温度为298K，浓度分别为0．87mol／L、2．2mol／L和4．1mol／L的NaCl溶液进行了研究，考察了浓度对溶液微观结构和动态性质的影响。模拟发现，浓度对离子近程水化的结构有一定的影响，随着溶液浓度的增加O-O径向分布函数变化显著，高浓度时水分子周围不再有明显的第二配位圈。MD模拟得到的溶液微观构型的图像显示，Na^ 水化圈内的水分子以氧原子靠近阳离子，Cl^-水化圈内的水分子以氢原子靠近阴离子。Na^ 的水化数随着溶液浓度的增加逐渐减小，Cl^-的水化数随着溶液浓度的增加逐渐变大，水分子在阴离子和阳离子的水化圈内的停留时间均随着电解质浓度的增加而增加。溶液浓度的增加，加剧了离子微观反向运动的振荡，自扩散系数降低。

Molecular Dynamics Simulations of Concentration Effects on Aqueous NaCl Solutions

A series of constant-temperature molecular dynamics simulations of aqueous NaCl solutions at different salt concentrations, ranging from 0.87 mol/L to 4.1 mol/L, was carried out to investigate the structural and the dynamical properties. It was found that significant structural changes occurred in the oxygen-oxygen radial distribution function of water molecules and no well-defined second hydration shell was found around a central water molecule with increasing ion concentration. The orientation of water molecules in the first hydration shell could be seen in visualizations of the equilibrium configurations of the solution. The hydration numbers of positive ions were found to decrease and that of negative ions increased gradually at higher ion concentrations. The residence times of water molecules near ions showed that an increasing trend as the ion concentration was increased. An increase of ion concentration led to an enhancement of the oscillations in the microscopic dynamics of the molecules and the self-diffusion coefficients of both ions and solvent molecules decrease with ion concentration.