Abstract Owing to advanced power electronic and electrical applications developing towards miniaturisation and integration, the thickness‐dependent DC breakdown mechanism of epoxy/multiwall‐carbon‐nanotube nanocomposites is under investigation. The results indicate that the breakdown strength of nanocomposites containing 0.05 wt% multiwall‐carbon‐nanotubes rises by ∼18%, and the breakdown strength falls exponentially with increasing thickness. To clarify the microscopic mechanism, a simulation model of DC breakdown, including carriers transport and segmental dynamics, is developed, and the accordant simulation results with experimental results indicate that the thickness‐dependent DC breakdown of epoxy/multiwall‐carbon‐nanotube nanocomposites is determined both by segment chain dynamics and charge transport. According to the breakdown model analysis, the effects of multiwall‐carbon‐nanotube on enhanced breakdown strength are caused by the increased amount of deep traps in the interfacial region, while the influence of thickness is attributed to the enlarged segment chain displacement and electric field distortion as the voltage raising time increases.
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