On the Effect of Nanoparticle Surface Chemistry on the Electrical Characteristics of Epoxy-Based Nanocomposites

The effect of nanosilica surface chemistry on the electrical behavior of epoxy-based nanocomposites is described. The nanosilica was reacted with different volumes of (3-glycidyloxypropyl)trimethoxysilane and the efficacy of the process was demonstrated by infrared spectroscopy and combustion analysis. Nanocomposites containing 2 wt % of nanosilica were prepared and characterized by scanning electron microscopy (SEM), AC ramp electrical breakdown testing, differential scanning calorimetry (DSC) and dielectric spectroscopy. SEM examination indicated that, although the nanoparticle dispersion improved somewhat as the degree of surface functionalization increased, all samples nevertheless contained agglomerates. Despite the non-ideal nature of the samples, major improvements in breakdown strength (from 182 ± 5 kV·mm^-1 to 268 ± 12 kV·mm^-1) were observed in systems formulated from optimally treated nanosilicas. DSC studies of the glass transition revealed no evidence for any modified interphase regions between the nanosilica and the matrix, but interfacial effects were evident in the dielectric spectra. In particular, changes in the magnitude of the real part of the permittivity and variations in the interfacial α'-relaxation suggest that the observed changes in breakdown performance stem from variations in the polar character of the nanosilica surface, which may affect the local density of trapping states and, thereby, charge transport dynamics.