Guan Yongji, Clark Ryan, Philippi Frederik, Zhang Xiaoping, Welton Tom
Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, White City Campus, London W12 0BZ, United Kingdom.
Institute of Optoelectronics and Electromagnetic Information, School of Information Science and Engineering, Lanzhou University, Lanzhou, Gansu 730000, People's Republic of China.
J Chem Phys. 2022 May 28;156(20):204312. doi: 10.1063/5.0091322.
Ionic liquids (ILs) are novel promising materials widely used in various fields. Their structures and properties can be tuned by means of external perturbations, thus further broadening their applications. Herein, forces proportional to atomic mass (mass-related field) and atomic charge (electric field) are applied in molecular dynamics simulations to the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide to investigate the origin of the resulting changes in structures and dynamics. The results show that both electric and mass-related fields cause the ion cages to expand and deform, eventually leading to their breakdown to produce a transformation of ILs from the cage structure to a channel-like structure, which results in faster self-diffusion of ions in the directions of the applied force and to a lesser extent other directions. Further comparison of electric and mass-related fields demonstrates that only the electric fields reorientate cations to produce a hydrodynamically favored conformation in the force direction, which shows faster diffusion. The cis isomer of the anion is preferred in the presence of the electric fields, whereas applying the forces proportional to mass does not change the anion conformer equilibrium significantly. The results presented in this work aid in the understanding of how ions adjust their structures to adapt to external perturbations and facilitate the application of ILs as electrolytes.
离子液体（ILs）是一类新型的、具有广阔应用前景的材料，广泛应用于各个领域。它们的结构和性质可以通过外部扰动进行调节，从而进一步拓宽其应用范围。在此，在分子动力学模拟中，将与原子质量成正比的力（质量相关场）和与原子电荷成正比的力（电场）应用于离子液体1-丁基-3-甲基咪唑双（三氟甲基磺酰）亚胺，以研究结构和动力学变化的起源。结果表明，电场和质量相关场都会导致离子笼膨胀和变形，最终导致其破裂，使离子液体从笼状结构转变为通道状结构，这导致离子在作用力方向上的自扩散加快，在较小程度上也在其他方向上加快。对电场和质量相关场的进一步比较表明，只有电场会使阳离子重新定向，从而在力的方向上产生有利于流体动力学的构象，扩散速度更快。在电场存在的情况下，阴离子的顺式异构体更受青睐，而施加与质量成正比的力不会显著改变阴离子构象异构体的平衡。这项工作的结果有助于理解离子如何调整其结构以适应外部扰动，并促进离子液体作为电解质的应用。
