气体分子在聚氯代对二甲苯中渗透行为的数值模拟

Numerical Simulation on the Penetration of Gas Molecules in Poly(Chloro-p-Xylylene)

用数值模拟方法对气体分子在聚氯代对二甲苯(Parylene C)中的溶解、扩散和渗透行为进行了研究。构建了含300个对二甲苯单元的聚氯代对二甲苯分子链模型,经结构优化处理,获得了具有一定有序性,密度、玻璃化转变温度与实验数据接近的聚合物分子链结构模型。计算了该聚合物中的自由体积,结果表明Parylene C聚合物具有很小的自由体积,不易形成分子渗透的有效通道,这是其具有高气体阻隔性能的重要原因。结合分子动力学(MD)和巨正则蒙特卡洛方法(GCMC),计算获得了几种气体分子在Parylene C中的扩散系数、溶解系数和渗透系数,发现相比H2、He、O2、N2等分子,H2O分子更易被Parylene C聚合物吸附溶解。分子动力学模型说明在Parylene C聚合物中,气体扩散和渗透符合跳跃机理。

Numerical simulations were performed to study the solubility,diffusion,permeability of gas molecules in Poly(chloro-p-xylylene)(Parylene C).A model of the molecular chain for Parylene C with 300 repeat p-xylene units was established and structural optimized with molecular dynamics(MD),ordered structure was obtained,the density and glass transition temperature of the structure calculated from the optimized model were consistent very well with experimental values,which meant that the model could be applied to simulate the practical polymer in this numerical study.The free volume and its distributions in the polymeric model was obtained using Atom Values & Surfaces tool of the MS software,and the results indicate that the Parylene C has small free volume.It is not easy to form the available channel for gas molecules penetration,which is important reason why Parylene C has high gas barrier property.The diffusion,solubility and permeability coefficients of some gaseous molecules in the model were also calculated based on the combined methods of Molecular Dynamics(MD) with Great Canonical Monte Carlo methods(GCMC).The simulated data also shows that the H2 O molecules are more easy to be absorbed by Parylene C than H2,He,O2,N2.The trajectories of gas diffusing in the model demonstrate that the molecules transfer or move in polymer with a 'hopping diffusion'behavior.