温度对吡啶离子液体性质影响的分子动力学模拟研究

The influence of temperature on the properties of pyridinium ionic liquids studied by molecular dynamics simulation

运用分子动力学模拟方法研究了温度对三种吡啶离子液体[BPy][BF_4]、[HPy][BF_4]、[OPy][BF_4]热力学性质的影响,得到了每个体系的密度、自扩散系数、电导率和黏度等.研究结果表明:随着温度升高,同一种离子液体的密度减小,阴阳离子的自扩散系数明显增大,电导率升高,而黏度降低.在同一温度下,随着阳离子上烷基链的增长,离子液体的密度减小,但热力学性质的变化规律并不完全同步.烷基链长最短的[BPy][BF_4]的自扩散系数和电导率在每个温度下均为最大,而黏度最小;但烷基碳链更长的[OPy][BF_4]和[HPy][BF_4]的各种性质相差不大,甚至当温度大于323 K时,烷基链较长的[OPy][BF_4]的自扩散系数比[HPy][BF_4]的大.

The influences of temperature on the thermodynamic properties of pyridinium ionic liquids [ BPy ] [ BF4 ], [ HPy] [ BF4 ] and [ OPy] [ BF4 ] were studied by molecular dynamics simulation. Densities, diffusion coefficients, electrical conductivities and viscosities of three simulation systems were calculated. The results show that, when the temperature of the system rises, the density and the viscosity decrease, and the self- diffusion coefficient and the conductivity increase obviously. Under the same temperature, the density values decrease with cationic alkyl chain length increasing. However, the changing law of the thermodynamic properties is not syn- chronous. The self- diffusion coefficient and the conductivity of [ BPy] [ BF4 ], whose alkyl chain length is the shortest, are the largest at each temperature, but the viscosity is minimum. And various properties of [ OPy ] [ BF4 ] and [ HPy ] [ BF4 ] are similar, although the alkyl carbon chain of [ OPy ] [ BF4 ] is longer than that of [ HPy] [ BF4 ]. Even when the temperature is greater than 323 K, the self - diffusion coefficient of [ OPy] [ BF4 ] larger than that of [ HPy ] [ BE4 ]