Simulation Of Dispersion Of Carbon Nanotubes In Water Under Thermal Excitation

Carbon nanotubes(CNTs)have excellent thermal,mechanical,electrical and optical properties,which have attracted wide attention of scholars from all circles,especially single single-walled CNTs with the best performance.The morphology of carbon nanotubes has great influence on their excellent properties.One of the most important problems affecting the performance of carbon tubes is dispersion problem.Due to the high aspect ratio of carbon nanotubes,the van der Waals effect between tubes,and the defects of the preparation technology,the carbon nanotubes are easily entangled and formed into carbon tube clusters,which leads to the significant low dimensional properties of carbon nanotubes that cannot be fully utilized in future applications.Therefore,in the research and application of the properties of carbon nanotubes,the solution of dispersion problem has become a priority.Most of the existing dispersing methods open the carbon tube clusters by physical means or chemical treatment.However,the traditional methods still have many shortcomings: for example,the traditional physical means will break the carbon tube and lose the characteristics of the high aspect ratio of the carbon tube,and the traditional chemical treatment will often introduce more impurities and destroy the perfect structure of the carbon nanotubes,thus reducing their intrinsic properties,not to mention the performance of the performance.In previous studies,we proposed the idea that carbon nanotube clusters could be dispersed in water by thermal excitation.In the form of heat energy,the tubes were dispersed through the explosion boiling of water to achieve the purpose of dispersion without introducing any impurities.Based on this assumption,this paper uses molecular dynamics method to explore the dispersed movement of carbon nanotube bundles in water under thermal excitation.In the first part,the influence of the confined space inside carbon nanotubes on the water substructure and distribution is studied.Although the structure of water molecules is simple,compared with other liquids,water molecules have more unsound solid structure,high surface tension,high specific heat and other special properties.Water molecules often show unusual properties and states in the confined space.The space inside the carbon tube is a natural confined space.The hybrid system of carbon nanotubes/water is also the focus of research.In the first part,the effects of tube diameter,chirality and temperature on the structure and distribution of water in the cavity of single-walled carbon nanotubes were investigated by molecular dynamics method.The results show that at room temperature,the single-walled carbon nanotubes with diameters ranging from 1.018 nm to 1.253 nm tend to form an ordered polycyclic water structure in the tubes,but it is difficult to form an ordered water structure outside this range.Moreover,with the increase of pipe diameter,the structure of multi-ring water changes from ternary ring to six-membered ring.Van der Waals potential distribution analysis shows that water molecules tend to distribute close to the wall of carbon nanotubes and form the ordered structure of water in the above range of tube diameter.Compared with the carbon nanotubes with small diameter difference,the chirality of the nanotubes has little effect on the structure of the multi-annular water.The stability of the polycyclic water structure is temperature-dependent,and the ordered structure of the polycyclic water in the larger diameter carbon nanotubes is more likely to disappear with the increase of temperature.The second part is to explore the diffusion of water molecules between carbon tube bundles.The carbon tubes prepared by experiment seldom exist in the form of single tubes,and most of them are in the form of bundles.The diffusion of water molecules in the gap between carbon tubes is of practical significance for the study of water-dispersed carbon nanotubes.The results show that the water molecules can penetrate into the gap between the carbon tubes at room temperature,and the increase of temperature is beneficial to accelerate the diffusion of water molecules.In the third part,the dispersion behavior of carbon nanotubes in water at high temperature was investigated.According to the analysis of atomic distribution,temperature distribution and mean azimuth shift,the higher the temperature is,the better the dispersion effect is.The dispersion effect of the carbon tube at 800 K is better than that at other temperatures,and there is no aggregation after dispersion in the simulation time.Through the above work,we can see that the method of carbon nanotubes dispersion in water under thermal excitation is feasible,and the carbon tubes do not reaggregate,which is of great significance for the dispersion of carbon nanotubes.