Self-Healing Versus Local Specific Density in Metalized-Film Polypropylene Capacitors: A Reactive Molecular Dynamics Investigation

Self-healing occurs in metalized-film capacitors after electrical breakdown, thanks to the unique chemical properties of their insulating polymeric films. Polypropylene (PP) is the most successful self-healing polymer because it produces the largest fraction of volatile products, whose electrical conductivity is negligible. Similar to other insulating films, PP exhibits structural defects and voids, which are responsible for local density gradients and foster dielectric breakdowns. Herein, we investigate how specific density impacts the chemical processes constituting the self-healing of PP at high temperatures and pressures. The reactive (ReaxFF) molecular dynamics Hamiltonian was used to propagate atomic movements over time. We report that local density reduction boosts self-healing efficacy. A fraction of gas molecules formed −H2, C2H2, C2H4, and CH4─is inversely proportional to the initial PP density. In turn, the sizes of the soot species (carbon-rich unsaturated aliphatic and aromatic molecules) modestly depend on the pressure and gas densities. While the soot particles merge and thereby increase in mass upon cooling the system after dielectric breakdown, their largest directly observed sizes in no simulation exceeded ∼4% of the system size.