A molecular dynamics simulation of pressure-driven gas permeation in a micropore potential field on silica membranes
A molecular dynamics simulation of pressure-driven gas permeation in a micropore potential field on silica membranes
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DOI：
10.1016/j.memsci.2007.01.039
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发表时间：
2007-04-20
影响因子：
9.5
通讯作者：
Tsuru, Toshinori
中科院分区：
文献类型：
--
作者：
Yoshioka, Tomohisa;Asaeda, Masashi;Tsuru, Toshinori
采用分子动力学模拟方法研究了压力驱动气体透过玻璃SiO2膜的机理。利用改进的Born-Mayer-Huggins（BMH）对势和Stillinger-Weber（SW）三体相互作用，采用熔融淬冷法制备了虚拟非晶SiO2膜。采用双控制平面非平衡分子动力学（DCP-NEMD）方法模拟了上游压力恒定时的气体渗透现象，渗透分子被模拟为Lennard-Jones颗粒。氦和CO2分子的渗透率对温度和孔径的依赖关系进行了研究。对于直径为8和6埃的圆柱形孔，计算的氦分子渗透的温度依赖性与正常努森渗透机制预测的趋势相似，而在CO2渗透的情况下，观察到的温度依赖性大于氦和努森机制的显着偏差。对于较小的6埃孔模型，偏差更明显。一个考虑孔壁势场影响的简单气体渗透模型较好地解释了CO2在高温区的渗透特性。并从横向电位和密度分布的角度探讨了渗透机理。根据观察到的气体渗透速率的温度依赖性并使用简单的气体渗透模型预测的微孔内的势值与给定势参数产生的势场深度非常一致。研究结果还表明，密度（压力）之间的孔隙入口和出口，这可能是由一个有吸引力的孔壁电位增强，可能是渗透的真正驱动力，特别是在高温区域的孔隙的差异。(c)2007 Elsevier B. V.保留所有权利。
The mechanisms involved in pressure-driven gas permeation through a micropore on vitreous SiO2 membranes were examined molecular dynamics (MD) simulation. Virtual amorphous SiO2 membranes were prepared by the melt-quench method utilizing modified Born-Mayer-Huggins (BMH) pair potential and Stillinger-Weber (SW) three-body interactions. A dual control plane non-equilibrium MD (DCP-NEMD) technique was employed to simulate gas permeation phenomena under a constant upstream pressure, in which the permeating molecules were modeled as Lennard-Jones particles. The dependencies of the permeance of helium and CO2 molecules on temperature and pore size were examined. For cylindrical pores about 8 and 6 angstrom in diameter, the calculated temperature dependencies for the permeance of helium molecules were similar to the tendencies predicted by the normal Knudsen permeation mechanism, while in the case Of CO2 permeation, a temperature dependency larger than helium and a significant deviation from the Knudsen mechanism were observed. The deviation was more obvious for the smaller 6 angstrom pore model. A simple gas permeation model that takes the effect of the pore wall potential field into consideration satisfactorily explained the permeation properties Of CO2 in the high temperature region. The permeation mechanism was also examined from the viewpoint of the lateral potential and density distribution in a micropore. The values for the potential within micropores, predicted from the observed temperature dependencies of the gas permeation rate and using the simple gas permeation model, were in good agreement with the depth of the potential field resulting from the given potential parameters. The findings also indicate that the density (pressure) difference in a micropore between the pore entrance and exit, which could be enhanced by an attractive pore wall potential, might be the true driving force for permeation, particularly in the high temperature region. (c) 2007 Elsevier B.V. All rights reserved.