Higher hydrogen fractions in dielectric polymers boost self-healing in electrical capacitors.

Abstract

Electrical capacitors are omnipresent in modern electronic devices, in which they swiftly release large portions of energy on demand. The capacitors may suffer from arc discharges due to local structural heterogeneities in their components and inappropriate exploitation practices. High energies of the arc discharge are transferred as phonons to the electrode and dielectric film, which burn out locally. The dielectric breakdown takes place. The complete burnout leads to the isolation of the failed region and the capacitor's self-healing. The emerging soot can form a semiconducting channel and damage the capacitor. The efficiency of self-healing depends on the dielectric properties of the soot and its amount. We employ reactive molecular dynamics simulations to reveal the regularities of the high-temperature polymer destruction and record by-products emerging during this process. We found the formation of multiple volatile low-molecular compounds and contaminated quantum carbon dots (CQD) designated as soot. The percentage of carbon in soot is higher compared to the polymer. Furthermore, the CQD contains numerous unsaturated C-C bonds and aromatic C6-rings suggesting an enhanced electrical conductivity. The size of the CQD depends on the available volume, i.e., on the spatial scale of the dielectric breakdown. The elemental composition of the soot is unique for each polymer. Polypropylene undergoes the most efficient self-healing thanks to containing a large molar fraction of hydrogen atoms. The results are addressed to the experts in electrical engineering and polymer fine-tuning.