Electron scattering by Coulomb interactions of coupling agents for high insulating aramid films

Abstract

To optimize the dielectric properties of poly(m-phenylene isophthalamide) (PMIA), nanodiamond (ND) particles are incorporated as doping fillers. However, they often cause issues like uneven dispersion, filler aggregation, interfacial incompatibility, and dielectric mismatch. To address these issues, three coupling agents of (3-Aminopropyl)triethoxysilane (KH550), triethoxyvinylsilane (KH151), and nonafluorohexyltriethoxysilane (F-agent) are utilized to modify ND. Among them, the F-agent modified PMIA/ND composite film shows the best performance, achieving a Young’s modulus of 5.8 GPa and a breakdown strength of 342 kV/mm at 15 wt% doping. The F-agent enhances the ND dispersibility due to an increased Zeta potential, effectively mitigating filler agglomeration. Its fluorine-containing functional groups engage in robust hydrogen bonding with PMIA molecules, strengthening interfacial interactions and compatibility. This promotes a dense and compact structure conducive to a uniform electric field distribution and confines dipole activities for a reduced dielectric loss. Moreover, the negative surface potential of the F-agent induces repulsive Coulomb interactions with free electrons, leading to the carrier scattering effect that shortens the mean free path of electrons and impedes charge transport. Therefore, the leakage current is highly suppressed for a high breakdown strength. These findings provide valuable insights and guidelines for designing high-performance aramid-based dielectric composites.