In Situ Autofluorescence Imaging Unveils Interfacial Confinement Effect on Electrical Treeing in Multiphase Polymers

In the field of multiphase polymer interface science, electrical tree damage remains a critical scientific challenge for maintaining insulation reliability. However, the limited spatial resolution of existing characterization techniques has impeded in situ 3D visualization of interfacial electrical trees, significantly restricting mechanistic investigations into their evolution. This study reports the observation of autofluorescence in non-fluorescent polymers, such as cross-linked polyethylene (XLPE) and silicone rubber (SIR), specifically localized within electrical tree damage zones. Confocal scanning microscopy enabled 3D imaging with nanoscale resolution without exogenous fluorescent probes, and successfully monitored the real-time morphology of electrical trees. Electrothermal coupling induces polymer chain scission, resulting in the formation of π-π^* conjugated structures in XLPE and cyclic siloxane oligomers in SIR. These molecular alterations markedly reduced the energy gaps of frontier molecular orbitals (ΔE), decreasing by 4.4-4.61 eV in XLPE and 1.84-2.56 eV in SIR, thereby enhancing autofluorescence intensity via radiative transitions. Notably, interfacial confinement effects restricted XLPE chains into compact conformations, forming an insulating barrier that inhibited vertical penetration of electrical trees while promoting lateral expansion along the interface. This method uniquely integrates 3D visualization and non-destructive evaluation capabilities, establishing a versatile platform for investigating interfacial failure mechanisms in multiphase insulation systems.