Electric Field-Stimulated Autofluorescence for In Situ 3D Characterization of Polymer Defects

The absence of in situ detection approaches for internal defect structures in polymers (such as microscale fillers, voids, and electrical trees) has long impeded advanced materials characterization. Herein, it is demonstrate that moderate electric fields can selectively induce intense autofluorescence at defect sites within various polymers, including epoxy resins, polyethylene, silicone rubber, and polydimethylsiloxane. Such defects may evolve gradually in polymeric materials under intense electric field stress. In later stages, they can generate significant ionizing radiation, accelerating material degradation and failure. Integrating electric field-stimulated autofluorescence with confocal laser scanning microscopy enables early detection of such defects via three-dimensional (3D) autofluorescence imaging prior to severe irreversible damage. This approach achieves submicron 3D resolution, facilitating high-clarity real-time visualization of electrical tree defect dynamics. Multiscale analyses reveal that external electric fields enhance intermolecular orbital overlap, resulting in reduced HOMO-LUMO energy gaps and attenuated electrostatic potential gradients on the molecular surface. These effects promote exciton-dominated fluorescence amplification under 552 nm excitation. Compared with existing characterization techniques, this probe-free method offers significant advantages, including in situ and three-dimensional imaging capabilities, thereby establishing a broadly applicable platform for analyzing microscale structures in polymers.