Abstract
The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.
Highlights
Fluid transport properties in nanochannels have attracted extensive attention [1,2,3]
Fasano et al [9] simulated the diffusion behavior of water molecules in carbon nanotube arrays, and they found that the diffusion coefficient of fluid water was related to the size of the nanochannels and the change in the diffusion coefficient of water molecules could be controlled by inducing an electric field
Liu et al [10] investigated bon nanotube arrays, and they found that the diffusion coefficient of fluid water was related to the size of the nanochannels and the change in the diffusion coefficient of water molecules could be controlled by inducing an electric field
Summary
Fluid transport properties in nanochannels have attracted extensive attention [1,2,3]. There are some reportsofon the influence surface effects on the fluid diffusion be- of self-diffusion coefficient water along the of channel direction was about times that havior in micro-nanochannels. Reported thatcarbontitanium covered channels was hydrophobic, it enhanced the diffusion characteristics of the dioxide (TiO2 ) nanochannels werebut hydrophilic, and the liquid water formed hydrogen water molecules. There are few reports on the diffusion of the fluid in modified used toCurrently, simulate the self-diffusion behavior of water characteristics in the hydroxylated and silanized silica nanochannels. A qualitative description of the relationship to simulate the self-diffusion water in the hydroxylated and silanized silica between the number of silanizedbehavior chains onofthe channel wall and the diffusion coefficient chain lengths. The diffusion behavior described paper refers to number of silanizedbehavior chains on wallunder and the coefficienttherof the thethe dynamic self-diffusion of the fluidchannel molecules the diffusion action of molecular fluid water was obtained. Ability isThe evaluated by the diffusion mechanism [13], where the mean square displacement of water molecules is proportional to time andModel the diffusion ability is evaluated by the diffusion coefficient
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