Abstract: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 1 -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.

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This paper follows our investigation on the interfacial region within nanodielectrics. Fourier Transform Infrared spectroscopy and Raman spectroscopy were used to analyse the effects of modifying nanofiller with coupling agent. Specifically, silane chemistry was used to treat nanosilica samples; by functionalising nanofiller to different degrees and introducing this into an epoxy matrix, a series of nanocomposite systems were prepared and examined. The dispersion state of the treated nanofiller in epoxy was observed using Scanning electron microscopy, where the optimum distribution was found at a ratio of 4:1 (nanosilica to silane) and the ac breakdown strength is reported to improve with uniformity in dispersion.

The potential of polymeric nanocomposites as solid insulation systems has been a topic of great discussion. Although this approach as a means to engineering materials with improved properties has been well established, many of the fundamentals aspects of this class of materials remains poorly understood. For example, the long term dielectric characteristics of so-called nanodielectrics is one of these topics. Whilst the nature of the interfacial region within such systems is believed to be key in determining performance, further investigation is required in order better to understand the macroscopic behaviour of nanocomposites. Such studies are vital for fundamental change, bringing an alternative to conventional polymers and filled composites and so making a massive impact on industry.This paper concerns interfaces in nanodielectrics and sets out to explore the effect of quantified changes in surface functionalisation. Specifically, we have used vibrational spectroscopy to examine and characterise the relevant effects of modifying the surface chemistry of nanosilica with commercial silane methods. Confocal Raman spectroscopy is used to provide qualitative data concerning the functionalization level, whilst Fourier Transform Infrared spectroscopy is used to provide more quantitative data. In this paper, we present the first step towards the design and quantification of nanoparticle surface chemistry -a step that we believe will ultimately allow the interphase to be optimized to meet demanding dielectric requirements.