Theoretical Study On Characteristics Of Self-diffusion In Slit Nanopore Based On The Quasicrystal Structural Model Of Liquid

With the development of nanotechnology, the study on properties of fluids confined innanopores has attracted more and more attention. As transmission performances of fluids innanopores have an important influence on the membrane separation, oil exploration, thedevelopment of porous materials, catalysis, adsorption, environmental protection, medical,and pharmaceutical ect, The diffusion coefficient is an important parameter in the processes ofchemical production, research and design, which is a feature of diffusion behavior for fluids.Only if the structural characteristics and dynamics behaviors of fluid in nanopores could beunderstood from the perspective of molecule level, it can provide some guidance for practicalapplication. Most researchers use molecular dynamics and monte carlo simulation method toinvestigate the diffusion behavior of fluids in nanopore. However these methods can notreveal the mechanism of transmission performance in nanopore, a pressing need exists todevelop corresponding theories.Based on the optimized quasicrystal structural model of liquid, the effective potentialenergy of the molecules of liquids which are at the original balance position and in transitionprocess was calculated, and combined with correction formula of Erying’s viscosity, theexpression of viscosity in slit nanopore was deduced. Then the expression of self-diffusion inlayer of liquid confined within slit nanopore was derived by using the relationship betweenself-diffusion coefficient and viscosity of liquid, which derived from hydromechanics theoryand Erying’s activation theory. According to the definition of diffusion, average diffusioncoefficient of stratified fluids. Furthermore, the self-diffusion coefficient expression of liquidsconfined in slit nanopore was deduced.The self-diffusion coefficient in the nanopore was compared with that in free space, andthe effects of pore walls, pore widths, density, and temperature on the self-diffusioncoefficient were all investigated and discussed. The results indicated that the self-diffusioncoefficient of liquids in nanopore increased with the increasing of pore widths. As the porewidths increased, the self-diffusion coefficient in slit nanopore would be close to that in freespace. Similar to that in free space, the self-diffusion coefficient in nanopore decreased withthe increasement of density, and increased with the increasement of temperature. However theimpact of density on self-diffusion coefficient was not strong as that in free space. Except thepore which only accommodate one layer liquids, the pore width has no infulencement on theself-diffusion coefficient of liquids close to the pore wall. The influence of temperature on theself-diffusion coefficient of liquids close to the pore wall in different widths of pore was the same. The liquid which tightly attached to the pore wall was solid-state. The phase behaviorof the liquid in the slit nanopore depend on the size of the pore width. These phenomena arewell explained from the perspective of theory study, which would play an important guidancefor the study on the characteristics of self-diffusion coefficient in nanopore.