基于第一性原理的表面氟化聚乙烯界面势垒特性研究

Interfacial Barrier Characteristic of Surface Fluorinated Polyethylene Based on First Principle

为了从分子层面解释表面氟化聚乙烯相比于聚乙烯空间电荷更少的原因,采用第一性原理对构建的表面氟化聚乙烯模型进行计算。探讨了分子模型的静电势能分布、范德华表面局部电子亲和能、态密度和核-壳模型的轨道分布及平面平均静电势能,从微观角度对聚乙烯表面氟化界面的电子结构进行了分析研究。结果表明:聚乙烯的最低未占轨道(LUMO)具有链间特性,而氟化层具有链中特性。随着轨道序号的上升,轨道分布在二者界面呈现出从氟化层的链上转移至聚乙烯链间的过渡特征。聚乙烯本体具有负的电子亲和能,而氟化层具有正的电子亲和能,聚乙烯和氟化层结构界面处会形成电子势垒,起到抑制电子注入的作用。

In order to explain the reason why the surface fluorinated polyethylene has less space charge than the pure polyethylene from the molecular level, a surface fluorinated polyethylene model was built and calculated by first principle. The electrostatic potential energy distribution of the molecular model,the local electron affinity of van der Waals surface, density of states, and the orbital distribution and plane average electrostatic potential energy of core-shell model were discussed. The electronic structure of fluorinated interface on the polyethylene surface was analyzed from micro perspective. The results show that the lowest unoccupied orbit(LUMO) of polyethylene has inter-chain characteristics, while the fluorinated layer has intra-chain characteristics. With the increase of the orbital number, the orbital distribution characteristics on the interface transfer from the intra-chain of fluorinated layer to the inter-chain of polyethylene. The electron affinity of polyethylene is negative, while the electron affinity of fluorinated layer is positive, so that there is electronic barrier between fluorinated layer and polyethylene, which plays a role in inhibiting electron injection.