How interfacial strength affects dielectric performance in Silica/Poly(methyl acrylate) nanocomposites?

In dielectric nanocomposites, the key issue to reconciling high permittivity and high dielectric ratio is to clarify the underlying mechanism of interfacial dielectric behavior. In this work, we initially investigate how the surface chemistry of SiO2 may influence interactions with the matrix, the interfacial structure, and the dielectric performance of PMA, then study the effect of the SiO2 filling content on the structure and performance. We demonstrate that the introduction of SiO2 can induce the interfacial aggregation of the PMA chains, regulate the local conformation, and thus improve interfacial polarization ability. Too weak attraction arising from sparse hydrogen bonding cannot greatly influence the transformation of molecular conformation to achieve high dielectric permittivity. Excessive interaction originated from the dense hydrogen bonding and interfacial overlapping would anchor the polymer chains on the SiO2 surface and restrict the activity of dipole reorientation, leading to a negative effect on the dielectric ratio. To achieve an optimal effect of interfacial polarization, we find that the suitable interfacial adhesion energy of SiO2 is −100∼−110 kJ mol−1 nm−2, which positively impacts both dielectric permittivity and dielectric ratio. On the other hand, if the concentration of SiO2 is too high, it will produce the interfacial overlapping effect, resulting in the degradation of polarization ability and comprehensive dielectric properties.