A computational study on the charge-trapping characteristics of nano-silica-doped polydimethylsiloxane composites

Widely used as an insulating material in power cables, polydimethylsiloxane (PDMS) requires improved dielectric properties. Doping with nanoparticles is recognized as a feasible modification method, in which changes in charge-trapping characteristics are considered to be the key factor. However, the physical mechanism by which nanoparticles affect the charge-trapping characteristics of polymers is not yet fully understood. Using molecular dynamics, quantum chemistry, and first-principles methods, possible ways in which silica nanoparticles could affect the charge-trapping characteristics of PDMS are explored here. The results demonstrate that structural disorder in undoped PDMS results in electron traps of <0.4 eV and hole traps of <0.65 eV. After doping with silica nanoparticles, the changes in PDMS molecular structures are much smaller than those caused by the intrinsic structural disorder of PDMS. Therefore, the indirect effect by which silica nanoparticles change the charge-trapping characteristics of the polymer by affecting the structures of adjacent PDMS molecules is relatively weak. The results of first-principles calculations show that a 0.8 eV conduction band offset and a 1.4 eV valence band offset exist at the silica/PDMS interface region. These band offsets act as charge traps to block the charge transport process and change the charge-trapping characteristics of PDMS composites.