Tailoring interfacial crosslinking sites to improve the dielectric properties of epoxy/POSS nanocomposites

Interfacial characteristics are critical to the insulation performance of dielectric nanocomposites (NCs). However, the impact of physicochemical properties on interfacial characteristics and resultant dielectric properties is still unclear. In this study, the interfacial characteristics of epoxy resin/polyhedral-oligomeric-silsesquioxane (EP/POSS) are tailored by POSS functional groups, including octa-glycidyl (OG) and epoxycyclohexyl (ECH), to improve the dielectric performance. The characterization and experimental results show that the EP/OG-POSS exhibits better interfacial compatibility and dielectric performance than the EP/ECH-POSS. The molecular dynamic simulation results show that compared with the EP/ECH-POSS, the better interfacial compatibility of the EP/OG-POSS is derived from the intrinsically stronger interfacial interaction between the OG-POSS and EP, which results in a higher interfacial crosslinking degree and a more compact interfacial structure. It further reduces the free volume and mean square displacement of molecular chains. Thus, besides the self-crosslinking of EP matrix, the incorporation of the OG-POSS introduces more interfacial crosslinking sites, which can also act as deep traps for charges. The more the interfacial crosslinking sites, the deeper the traps. These deep traps hinder the charge transport, ultimately improve the volume resistivity and maintain uniform space charge distribution. Therefore, an effective approach is proposed to improve the charge-trapping behavior and dielectric properties of NCs by tailoring interfacial crosslinking sites.