مطالعات شبیه سازی ام دی در تأثیر ساختار غشا و پویایی بر خواص نفوذ گاز از طریق غشاء میکرو سیلیس آمورف

Imaginary amorphous silica membranes were prepared on a computer and gas permeation simulations were conducted using a dual control plane non-equilibrium molecular dynamics (DCP-NEMD) method. The Melt-Quench technique was employed to prepare various types of imaginary amorphous silica membranes which had different densities (from 1.3 to 2.2 g/cm3) and different mean pore sizes. Helium was adopted as a permeating gas species and its permeability was calculated at temperatures from 300 to 800 K. The Knudsen diffusion-like temperature dependencies of permeability could be observed for densities below 1.7 g/cm3, while the activated diffusion for the higher density models. We have also examined the effect of 3-body membrane potential parameters on membrane dynamics and gas permeation properties. The larger thermal vibration of oxygen atoms both in siloxane bonds and silanol groups on membranes could be observed for greater γ1 parameter is the SW potential function, which might result in the change of activation energy for gas permeation.

Sol–gel derived microporous amorphous silica membranes are assumed to have small openings formed by network of siloxane bonds (network pore) [1,2]. Small molecules such as helium and hydrogen are able to permeate through network pores, that exist in dense phase occupying the greater part of a silica membrane surface. Therefore, to reveal the amorphous silica structure and gas permeation characteristics of small molecules are important to develop silica based microporous gas separation membranes. Molecular simulations of gas permeation through microporous silica membranes have been already conducted bymany research groups to obtain useful findings[3–10]. In this work, the effects of silica membrane density andmembrane potential parameters on gas permeation properties were examined using molecular dynamics simulations from a microscopic point of view. Some dense amorphous silica membranes were fabricated using the Melt-Quench (MQ) method [11], and the permeation rate of He was calculated using a simple non-equilibrium molecular dynamics simulation technique. The goal of this work is to develop a molecular dynamics simulator which can reproduce gas permeation characteristics on real microporous silica-based membranes.

Virtual amorphous silica membranes were prepared and gas permeation simulations were conducted using DCP-NEMD method. The Knudsen diffusion-like temperature dependencies of permeance could be observed for membranes whose density was smaller than 1.7 g/cm3, while the activated diffusion for denser membranes. The size of pores from about 0.25 to 0.3 nm would be effective for activated diffusion behavior of helium, and pores of 0.35 nm or larger ones would lead to Knudsen-like diffusion. It was also suggested that both the static amorphous silica structure and dynamical characteristics of a membrane depended on the value of 1 parameter in the SW potential function, and that gas permeation properties through microporous silica membranes might be influenced by the thermal movement of silica network.