Molecular Dynamics Simulation Study On The Microscopic Structure And The Diffusion Behavior Of Fluid Molecules In Confined Carbon Nanotubes

Since the carbon nanotube was found, it has been becoming an important kind ofnonmaterial for its high Young’s modulus, good electrical and thermal conductivity,and unique optical and fluid transport properties. Nowadays Molecular DynamicsSimulation as a powerful tool to study dynamical properties of materials is generallyused in physics, chemistry, mechanics, electromagnetic and many other fields. Withthe rapid development of computer technology, it is also becoming one of the bestchoices to study this type of nano-materials. In this paper, we mainly focused on thedynamical properties and microstructures of the fluid in confined spaces. We chosethe confined spaces as carbon nanotubes and the fluid as methanol and water whichare often used in chemistry.Under isothermal and isobaric conditions, the microstructure and the diffusionproperties of the methanol in different pore sizes are studied. The result of the radialdensity distribution of the methanol shows that the order of the molecular position inthe inside the tubes are proportional to the size of the pore diameter. The hydrogenbond number and the coordination number have a direct link to the limited effect. Thediffusion coefficients of the methanol calculated with two different methods indicatesthat methane diffuses in Knudsen diffusion mode. We also have explored thedependence of water diffusion in carbon nanotubes on the pore diameter and thetemeperature. The results show that the diffusion coefficient of water increases asdiameter of carbon nanotubes increasing at the same temperature. The watermolecules inside carbon nanotubes with smaller diameter prefer to form a chainstructure linked with hydrogen bonds around the tube axis, whereas the watermolecules in the larger tubes are preferably gathered near the carbon nanotube wall.