Effect of Interfacial Polarization and Water Absorption on the Dielectric Properties of Epoxy-Nanocomposites

Abstract

Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm −1 . In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm −1 ; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm −1 . In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study.

Enhancement of the Insulation Properties of Poly(2‐oxazoline)‐co‐Polyester Networks by the Addition of Nanofillers

“…Despite the fact that the tendency of surface energies was not reproduced, the most striking observation was the fact that all materials, after an initial weight gain, showed weight losses with respect to the (intermediate) maxima. An analogous tendency has previously been observed in a corresponding study with epoxy‐amine resins and been referred to a structural reorganization of the polymer matrices upon the absorption of water . The initial water absorption was highest in the case of the nanocomposite with SiO 2 fillers, the surfaces of which have the highest abundancy of polar M‐OH groups (Figure ).…”

Heat Dissipation in Epoxy/Amine-Based Gradient Composites with Alumina Particles: A Critical Evaluation of Thermal Conductivity Measurements

“…In summary, the thermal conductivity at r.t. ranged from 0.25 to 0.45 W·m −1 ·K −1 ; unfilled epoxy-amine resins exhibit a thermal conductivity of approx. 0.2 W·m −1 ·K −1 [14].…”

“…Very few polymers with dedicated structural motifs show a higher thermal conductivity of 0.3 W·m −1 ·K −1 [11]. This characteristic can be overcome by the addition of fillers with high thermal conductivity [4,12,13,14]. Due to the low heights of films in power packages or insulation layers down to the μm range, such (inorganic) fillers are preferentially used in nano- and/or submicron-scaled sizes.…”

“…It must be taken into account that particles with diameters above the nano-scale may sediment in a composite material during the curing reaction, yielding a gradient composite with varying composition along the height scale (e.g., increasing content of inorganic fillers from top to bottom) and, consequently, an analogously varying thermal conductivity. The phenomenon of sedimentation eventually occurs to even higher extent due to the agglomeration of (non-functionalized) particles, despite their initial homogeneous dispersion in a polymer matrix [14].…”

Influence of filler/matrix interactions on resin/hardener stoichiometry, molecular dynamics, and particle dispersion of silicon nitride/epoxy nanocomposites

“…Compared with some other nanofiller types, the dispersion state shown here for Si 3 N 4 is much better. For example, the introduction of untreated silica, which is polar and, thus, can be considered compatible with the polar epoxy matrix, has been reported to produce particle agglomerations that can reach the microscale size [59,60]. Even for silica which was treated with a silane coupling agent terminated with an epoxy group, microscale particle agglomerations have been observed [36].…”