Correlation between Microstructural Instabilities and Dielectric Failure in LDPE Nanocomposites

This work investigates the link between nanoindentation pop-in events and short-time AC breakdown strength in low-density polyethylene (LDPE)alumina Nanocomposites (NCs) designed for high-voltage insulation. LDPE-alumina films with varying nanofiller volume fractions are prepared and their morphology, chemical groups, crystallinity, and surface topography are characterized using FE-SEM, FTIR, XRD and AFM analyses to contextualize mechanical and dielectric responses. Quasistatic Nano-Indentation (NI) technique is employed to obtain force-displacement curves, from which Hardness, plastic work, round-trip efficiency and pop-in events are extracted, revealing mechanical stress-induced microstructural and interfacial instabilities at higher filler loadings. Parallelly the dielectric failure is assessed through AC breakdown tests to obtain Weibull scale and shape parameters for each composite. Results show that alumina loading beyond an optimal level introduces mechanically weak interfacial regions that manifest as distinct pop-in events and larger irreversible indentation depths, accompanied by reduced AC breakdown strength. A clear correlation emerges between the onset/intensity of pop-in behaviour i.e., interfacial defect density, and the degradation of breakdown performance, highlighting that nanoindentation pop-ins can serve as a sensitive mechanical proxy for dielectric reliability in LDPE-alumina NCs.