QM/MD simulations on the role of SiO2 in polymeric insulation materials

Abstract

Quantum chemical molecular dynamics (QM/MD) simulations based on a self-consistent charge density functional tight-binding (SCC-DFTB) method on SiO₂ filler in polyethylene (PE) showed that: in the absence of SiO₂, the PE was quickly charged by high-energy electrons, which resulted in C–C or C–H bonds breaking; on the contrary, in the presence of SiO₂ nanoclusters, electron trapping and accumulating were dominated by SiO₂ nanoclusters rather than polyethylene, which made polyethylene be preferentially protected and increased the initial time of electrical treeing. In our calculations, we also observed double electric layers around the SiO₂ nanocluster, in agreement with recent suggestions from experimental observations. Furthermore, compared with some other investigated nanoclusters, SiO₂ was regarded as the most promising candidate attributed to the highest electron affinity. We further observed that once the high-energy electrons were supersaturated in the nanoclusters, the polyethylene chains would be unavoidably charged and C–H bond breaking would occur, which resulted from the interaction between H and O or Si in the nanoclusters. Following that, decomposing and cross-linking of the polyethylene chains were involved in the initial growth of electrical treeing. The current observation can potentially be used in power cable insulation.