Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University , SE-106 91 Stockholm, Sweden.
Theoretical Chemistry, Chemical Center, Lund University , P.O. Box 124, SE-221 00 Lund, Sweden.
ACS Appl Mater Interfaces. 2017 Feb 8;9(5):4976-4987. doi: 10.1021/acsami.6b14429. Epub 2017 Jan 27.
Atomistic molecular dynamics simulations have been performed to study microscopic the interfacial ionic structures, molecular arrangements, and orientational preferences of trihexyltetradecylphosphonium-bis(mandelato)borate ([P][BMB]) ionic liquid confined between neutral and charged gold electrodes. It was found that both [P] cations and [BMB] anions are coabsorbed onto neutral electrodes at different temperatures. The hexyl and tetradecyl chains in [P] cations lie preferentially flat on neutral electrodes. The oxalato and phenyl rings in [BMB] anions are characterized by alternative parallel-perpendicular orientations in the mixed innermost ionic layer adjacent to neutral electrodes. An increase in temperature has a marginal effect on the interfacial ionic structures and molecular orientations of [P][BMB] ionic species in a confined environment. Electrifying gold electrodes leads to peculiar changes in the interfacial ionic structures and molecular orientational arrangements of [P] cations and [BMB] anions in negatively and positively charged gold electrodes, respectively. As surface charge density increases (but lower than 20 μC/cm), the layer thickness of the mixed innermost interfacial layer gradually increases due to a consecutive accumulation of [P] cations and [BMB] anions at negatively and positively charged electrodes, respectively, before the formation of distinct cationic and anionic innermost layers. Meanwhile, the molecular orientations of two oxalato rings in the same [BMB] anions change gradually from a parallel-perpendicular feature to being partially characterized by a tilted arrangement at an angle of 45° from the electrodes and finally to a dominant parallel coordination pattern along positively charged electrodes. Distinctive interfacial distribution patterns are also observed accordingly for phenyl rings that are directly connected to neighboring oxalato rings in [BMB] anions.
采用原子分子动力学模拟方法研究了中性和带电金电极间三己基十四烷基膦双（扁桃酸根）硼酸酯([P][BMB])离子液体的界面离子结构、分子排列和取向偏好。结果表明，[P]阳离子和[BMB]阴离子在不同温度下均被共吸附到中性电极上。[P]阳离子中的己基和十四烷基链优先平躺吸附在中性电极上。[BMB]阴离子中的草酰基和苯基环在靠近中性电极的最内层混合离子层中呈现交替的平行-垂直取向。温度升高对受限环境中[P][BMB]离子物种的界面离子结构和分子取向的影响很小。在带电金电极中，分别导致[P]阳离子和[BMB]阴离子的界面离子结构和分子取向发生特殊变化。随着表面电荷密度的增加（但低于 20 μC/cm），由于[P]阳离子和[BMB]阴离子分别在带负电和带正电的电极上连续积累，在形成明显的阳离子和阴离子内层之前，混合最内层界面层的层厚逐渐增加。同时，同一[BMB]阴离子中两个草酰基环的分子取向逐渐从平行-垂直特征变为部分以与电极成 45°角的倾斜排列为主，最后沿带正电电极以主导的平行配位模式为主。相应地，与[BMB]阴离子中相邻草酰基环直接相连的苯基环也观察到了独特的界面分布模式。
