Polyolefin-Based Cross-Linked Networks for Self-Healing and Thermostable Capacitors

This study aimed to prepare liquid-filled hybrid network capacitors that are self-healing and maintain reliable performance at high temperatures by selectively cross-linking or branching polyethylene (PE) in the presence of low-molar-mass polypropylene (PP). PE was modified by reactive extrusion with different ratios of dicumyl peroxide in the presence of PP to prepare intermediates that could be injection molded into discs. During thermal processing, PE undergoes cross-linking or branching, while PP is known to undergo chain scissoring, resulting in the formation of a cross-linked or branched PE matrix that is responsible for improved thermostability. In contrast, the PP forms a mobile phase, which is responsible for self-healing. A range of peroxide concentrations was evaluated, confirming that structures from slightly branched to cross-linked could be obtained after extrusion and injection molding. Thin-film capacitors were subsequently fabricated by spin-coating inks on a conductive substrate and characterized to determine their dielectric performance. The optimal PE matrix structure was obtained with a low initiator loading, resulting in a branched structure with a relatively low dielectric constant (∼2.5), which resulted in improved thermostability up to 150 °C. Capacitor devices that experienced electrical breakdown were able to self-heal and function again after annealing at 160 °C.