Peng Hailong, Kubo Momoji, Shiba Hayato
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
Phys Chem Chem Phys. 2018 Apr 18;20(15):9796-9805. doi: 10.1039/c8cp00698a.
Molecular dynamics simulations are performed on a 1-dodecyl-3-methylimidazolium hexafluorophosphate ([C12mim][PF6]) ionic liquid using a united-atom model. The ionic liquid exhibits second step relaxation at temperatures below a crossover point, where the diffusion coefficient shows an Arrhenius to non-Arrhenius transition. Annealing below this crossover temperature makes an isotropic to mesophase transition, where the smectic A (SmA) phase or crystal-like smectic B (SmB) phase forms. Hundreds of nanoseconds are required for completing these transitions. A normal diffusion process is found for anions along the layer-normal and -lateral directions in the SmA phase, but only in the lateral directions in the SmB phase. We find a preserved orientational order for the imidazolium-ring rotational and the alkyl-chain reorientational dynamics in both of the smectic phases.
使用联合原子模型对1-十二烷基-3-甲基咪唑六氟磷酸盐（[C12mim][PF6]）离子液体进行分子动力学模拟。该离子液体在低于交叉点的温度下表现出第二步弛豫，此时扩散系数呈现出从阿仑尼乌斯型到非阿仑尼乌斯型的转变。在该交叉温度以下进行退火会发生从各向同性到中间相的转变，形成近晶A（SmA）相或类晶近晶B（SmB）相。完成这些转变需要数百纳秒。在SmA相中发现阴离子沿层法线和横向方向存在正常扩散过程，但在SmB相中仅沿横向方向存在正常扩散过程。我们发现，在两个近晶相中，咪唑环旋转和烷基链重取向动力学的取向有序得以保留。
