Molecular Dynamics Simulations Of Solution Confined In Nanotube

The confinement of micro-porous media,such as sol-gels,zeolites and carbon nanotube can lead to dramatic changes of liquid in their static and dynamic properties from those of the bulk system.To understand the special properties of confined fluids is not only meaningful in theoretical research,but also important in oil exploration,catalyst applications and many other fields.At the same time,with the development of computer science and technology, molecular dynamics sumulation can answer many questions emerged in experiment and becomes a useful guide to researcher now.In this dissertation,molecular dynamics simulations on the vibrational energy transfer and diffusion of I₂/Ar solution confined in a cylindrical nanotube have been presented.The radial density profiles of solvent and solute vibrational energy relaxation time,as well as the solvent diffusion coefficient along the nanotube are calculated as a function of radius of the nanotube.The results show that:1) T₁ decreases as the radius increases;2) D_z increases as the radius increases;3) The confinement effect of the nanotube weakens quickly as the radius becomes larger,and as a result,both T₁ and D_z tend towards the values of the bulk system.On the other hand,as an atomic system,the weak interaction between solute confined in single-walled carbon nanotube and the surrounding environment is more complicated.The quantum-classical dynamics simulation technique has been used to study the solute vibrational line shifts and its distributions as well as the spatial distribution of solvent atoms confined in single-walled carbon nanotube.The results show that:1) The environment-induced vibrational frequency of solute I₂ confined in SWNT is slightly blueshifted compared to the bulk system and increases as the radius increases;2) The solvent contribution to the line shift is bigger than that of SWNT;3) Only a few solvent can determine the frequency shift,which locate in three parts:the atoms with blueshifting are located around the end of I₂ molecule;the redshifting atoms are located in two places:one is near the end of the I₂ molecule in a linear geometry but at a significantly larger distance than the blueshifting argon atoms;the other is at small Ar-I₂ center-of-mass distance with a "T-shape" configuration in which argon atom is located above the center-of-mass of I₂.