Molecular modeling of electron trapping in polymer insulators
Molecular modeling of electron trapping in polymer insulators
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DOI：
10.1063/1.481802
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发表时间：
2000-07-01
影响因子：
4.4
通讯作者：
Quirke, N
中科院分区：
文献类型：
--
作者：
Meunier, M;Quirke, N
高压电缆聚合物绝缘中空间电荷的存在与电击穿有关。有大量的文献涉及空间电荷的实验表征以及空间电荷形成和放电的唯象模型。然而，分子性质、空间电荷形成和最终击穿之间的直接联系仍有待建立。在本文中，我们提出了一个新的计划，构成了连接微观缺陷的空间电荷的形成的第一步。虽然我们的目标是了解在分子水平上的缺陷的作用，在电子捕获和聚乙烯中的空间电荷的形成，我们开始考虑一个“模型”材料，蜡十三烷（n-C13 H28）。很明显，物理（例如，构象缺陷）和化学缺陷（例如，断裂的键）可能存在于绝缘材料中，并且都可能俘获电子。在本论文中，我们着重于物理缺陷的作用。我们的分析表明，通过定义的缺陷能量的分子电子亲和势，电子陷阱和材料的分子性质之间的关系建立。用密度泛函理论（DFT）计算了蜡分子的电子亲和势及其随分子构象的变化。通过对无定形蜡进行分子动力学模拟，我们能够确定可能的构象缺陷，并通过使用从头计算方法估计捕获能量。在这些蜡质材料的构象缺陷预测产生浅陷阱的能量低于0.3 eV。这些结果用于估计聚乙烯中构象陷阱中电子的能量、数量和停留时间。(C)2000年美国物理学会。[S0021-9606（00）70121-8]。
The presence of space charge in the polymeric insulation of high-voltage cables is correlated with electric breakdown. There is a vast literature concerned with the experimental characterization of space charge and with phenomenological models of space charge formation and discharge. However, a direct link between molecular properties, space charge formation and eventual breakdown has still to be established. In this paper, we suggest a new scheme that constitutes a first step in linking microscopic defects to the formation of space charge. Although our goal is to understand the role of defects at the molecular level in electron trapping and the formation of space charge in polyethylene, we start by considering a "model" material; the wax tridecane (n-C13H28). It is clear that both physical (e.g., conformational defects) and chemical defects (e.g., broken bonds) may be present in insulating materials and may both trap electrons. In the present paper, we focus on the role of physical defects. Our analysis suggests that by defining the defect energy in terms of the molecular electron affinity, a relationship is established between the electron trap and the molecular properties of the material. The electron affinity and its variation with wax molecule conformation have been calculated using density functional theory (DFT, as implemented in the code DMol). By performing molecular-dynamics simulations of amorphous waxes, we are able to determine likely conformational defects, and by using ab initio methods estimate the trapping energies. Conformational defects in these waxy materials are predicted to produce shallow traps with energies below 0.3 eV. These results are used to estimate the energy, number, and residence times of electrons in conformational traps in polyethylene. (C) 2000 American Institute of Physics. [S0021-9606(00)70121-8].