分子动力学模拟研究纳米碳管中甲醇-水混合溶液的结构与输运性质

利用分子动力学模拟方法,对比考察了平衡条件、外压作用、梯度电场作用下,摩尔比为1:1的甲醇-水混合溶液在纳米碳管(CNT)中的静态结构以及输运行为.研究发现:在平衡体系与外压作用下,纳米碳管内甲醇与水呈现出明显的不混溶现象,甲醇主要分布于管壁附近,水分子主要分布于纳米碳管轴心附近;而在梯度电场作用下,纳米碳管由疏水性向亲水性转变,更多的水分子分布于管壁,导致纳米碳管内甲醇-水的不混溶现象消失.另一方面,在外压作用下,纳米碳管内甲醇与水呈现单向移动;而在梯度电场下,甲醇与水呈现快速的双向移动,其流通量较相应外压作用体系高出近一个数量级,但由于双向的流通量大小相近,导致净流通量与外压作用下的净流通量差异不大.

Molecular Dynamics Simulation Study of Structural and Transport Properties of Methanol-Water Mixture in Carbon Nanotubes

Molecular dynamics simulations of a methanol-water mixture (molar ratio 1:1) were performed to determine the differences among the structural and transport properties in three carbon nanotube (CNT) systems: an equilibrium system, a system with an external pressure, and a system with a gradient electric field. The simulations showed that in both the equilibrium system and the system with an external pressure, the methanol-water mixture is clearly immiscible in the CNTs, with the water molecules distributed mainly around the tube axis, and the methanol molecules located near the tube wall; however, in the system with a gradient electric field, the hydrophobic CNTs become hydrophilic, and the phenomenon of methanol-water separation disappears. In contrast, unlike the unidirectional transport observed in the system with an external pressure, the particles move in two directions in the system with a gradient electric field, with a flow one order of magnitude larger than that in the corresponding external pressure system. However, in the system with a gradient electric field, the net flux is small, because the flows for the two directions are similar. There is thus a small flux difference between the system with an external pressure and the system with a gradient electric field.