单壁碳纳米管受限空间内水的分布

碳纳米管管腔作为分子物质的纳米通道,其储存或输送水的能力具有重要研究价值.为了研究碳纳米管管腔受限空间对水分子团簇结构和分布的影响,本文采用分子动力学方法探究了管径、手性和温度对单壁碳纳米管管腔内水的结构和分布的影响.结果表明:在常温下,管径尺寸范围为1.018—1.253 nm的单壁碳纳米管管内易形成有序的多元环水结构,此范围以外碳纳米管管内难以形成水的有序结构;且随着管径尺寸增大,多元环水呈现由三元环至六元环的结构变化;范德瓦耳斯势分布分析表明,在上述管径范围内,水分子趋向于贴近碳纳米管管壁分布而形成水的有序结构.对比管径尺寸差别较小的碳纳米管,其手性对多元环水结构影响不大.多元环水结构的稳定性表现出温度依赖性,管径较大的碳纳米管内的多元环水的有序结构更易随温度升高而消失.

Water distribution in confined space of single-wall carbon nanotube

Since the discovery of carbon nanotubes(CNTs),they have attracted extensive attention from scholars in various fields because of their excellent properties.The hollow-structured CNTs are often regarded as conduits and containers,which can act as nano-channels for various molecular substances in the membrane structure.As a source of life,water is indispensable to any living organism.In the application of carbon nanotubes as nanochannels,the most important is the ability of carbon nanotubes to store and transport liquids,especially nanoscaled aqueous solutions.Water molecular clusters in confined spaces exhibit unusual structures and properties.The study of special water structures in carbon nanotubes is of great theoretical importance in chemistry,biology and materials science.There are great difficulties in making the experiment on a nanoscale,but molecular dynamic simulation enables us to better study and analyze the structure and properties of water in confined space of CNT on a nanoscale.One has also studied the influence of temperature on the structure of water,but there are few studies focusing on the effect of temperature on the structure of water in confined space.Therefore,molecular dynamics simulation is used to investigate the effects of CNT diameter,CNT chirality and temperature on the water structure and distribution in a confined space.The simulation calculation is completed by GROMACS,the SPE/C water model is used for water molecules,and GROMOS9654a7 force field is used.Because of the presence of carbon nanotubes,water molecules tend to line up against the walls of the tubes,both inside and outside.In addition,water molecules tend to form highly ordered multiring structures in the carbon nanotubes with a size of 1.018–1.253 nm at a certain temperature.It is difficult to form the ordered structure of water in the outer carbon nanotubes.In the above range,with the increase of pipe diameter,the structure of multi-element ring water changes from three-element ring to six-element ring.On the one hand,the ordered structure depends on the diameter of the carbon nanotube,but the chirality of the carbon nanotube does not have a great influence on it.On the other hand,the stability of the ordered structure is temperature-dependent,and the ordered structure of multiple ring water in the carbon nanotube with a larger diameter is more likely to disappear with the increase of temperature.The van der Waals potential distribution is calculated by Multiwfn,and it is concluded that the van der Waals potential inside the tube is extremely low,resulting in a very large dispersion effect,and molecules can spontaneously move from the outer area to the tube.The van der Waals potential can also be negative outside the tube.This explains why water molecules tend to line up against the wall of the tube.