Space charge analysis and trap evaluation in silicone rubber by density functional study

摘要

This paper presents the fundamental characteristics of the electronic structures of silicone rubber (uncured SR) and cured (crosslinked) SR molecules. Localized states and trapping sites are evaluated by the molecular orbitals (MOs) and the density of state (DOS). The introduction of vinyl groups slightly changes the energy level distribution and introduces the electron-localized states (shallow trapping sites). However, it can be observed clearly that a hole trapping site (0.5 eV) is created by the benzene group. Moreover, some shallower trapping sites are also formed by the vinyl and the benzene groups alternately (0.3-0.4 eV). The cured SR molecular chains show a reduced energy gap compared with the uncured one. The crosslinked structures introduce the hole and the electron traps. Interestingly, a deep hole trapping site (1.2 eV) was found in the cured SR structure. These localized states or trapping characteristics are ascribed to the interaction of chains, the chemical groups and the crosslinks in the cured SR structure. Space charge of a virgin SR sample can be responsible for the trapping site characteristics, especially for the hole deep trap.