用分子动力学模拟研究阳离子链长对离子液体输运特性的影响

阐述了用分子动力学（molecular dynamics,MD）模拟方法研究在T=303K条件下[mmim][TFSA]、[emim][TFSA]、[bmim][TFSA]、[C6 mim] [TFSA]和[C8mim] [TFSA]5种离子液体的输运特性.模拟力场采用修正后的OPLS力场.根据模拟轨迹计算得到5种离子液体的密度值.根据均方位移（MSD）的斜率计算得到的离子液体阴阳离子自扩散系数.采用Nernst-Einstein （NE）方程计算得到离子液体摩尔导电率.这些模拟结果与实验值很吻合.离子液体的自扩散系数和电导率随着阳离子链长的增长而变小,主要原因是阳离子链长增长使离子液体中的氢键作用和范德华作用变强.计算所得离子液体摩尔导电率略大于实验测量值则归因于离子关联运动的结果.

Molecular dynamics simulations of ionic liquids and the influence of the cationic chain length on the transport properties

The molecular dynamics （MD） simulations of 5 ionic liquids [[mmim3 [TFSA], [emim] [TFSA], [bmim] [TFSA], （C6 mim] [TFSA] and （C8 mim~ （TFSA]] were described to explore the influence of the cationic chain length on the transport properties. The modified OPLS force field was choosed as simulations force field. The densities of ionic liquids were evaluated from MD trajectories; the self-diffusion cosefficients were determined by cal- culating the slopes of the MSDs of the ions; the ionic conductivity was calculated by the Nernst Einstein equation. All results from the MD simulations are coincided well with the experimental values. The self diffusion coefficients and the ionic conductivity of ionic liquids get smaller with the cationic chain become longer, which are attributed to the stronger hydrogen bonding and Van der Waals effects. The calculated molar conductivities of ionic liquids are slightly larger than the measured values, the reason are attributed to the result of the motional correlation.