Zou Jian, Ji Baohua, Feng Xi-Qiao, Gao Huajian
Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
Small. 2006 Nov;2(11):1348-55. doi: 10.1002/smll.200600055.
We recently reported the discovery via molecular-dynamic simulations that single-walled carbon nanotubes (SWCNTs) with different diameters, lengths, and chiralities can coaxially self-assemble into multi-walled carbon nanotubes (MWCNTs) in water via the spontaneous insertion of smaller tubes into larger ones. Here, we extend that study to investigate the various water structures formed between two selected SWCNTs after such coaxial assembly. Depending on the tube geometry, typical water structures, besides the bulk phase, include a one-dimensional (1D) ordered water chain inside the smaller tube, a uniform or nonuniform water shell between the two tubes, and a "boundary layer" of water near the exterior wall of the larger tube. It was found that a concentric water shell consisting of up to three layers of water molecules can form between the two SWCNTs, which leads to a class of carbon-water-carbon composite nanotubes. Analysis of the potential energy of the SWCNT-water system indicated that the composite nanotubes are stabilized by both the tube-tube and tube-water van der Waals interactions. Geometrically confined between the two SWCNTs, water mono- and bilayers are found to be stable, highly condensed, and ordered, although the average number of hydrogen bonds per water molecule is reduced. In contrast, a water trilayer between the two CNTs can be easily disrupted by thermal fluctuations.
我们最近通过分子动力学模拟报告了一项发现，即不同直径、长度和手性的单壁碳纳米管（SWCNTs）在水中可通过较小的管子自发插入较大的管子而同轴自组装成多壁碳纳米管（MWCNTs）。在此，我们扩展该研究以探究这种同轴组装后两个选定的SWCNTs之间形成的各种水结构。根据管子的几何形状，除本体相外，典型的水结构包括较小管子内部的一维（1D）有序水链、两根管子之间均匀或不均匀的水壳以及较大管子外壁附近的水“边界层”。研究发现，两根SWCNTs之间可形成由多达三层水分子组成的同心水壳，这导致了一类碳 - 水 - 碳复合纳米管。对SWCNT - 水系统势能的分析表明，复合纳米管通过管 - 管和管 - 水范德华相互作用得以稳定。尽管每个水分子的平均氢键数量减少，但在两根SWCNTs之间几何受限的单层和双层水被发现是稳定、高度凝聚且有序的。相比之下，两根碳纳米管之间的三层水很容易因热涨落而被破坏。
