A "Water Shell" Model for the Dielectric Properties of Hydrated Silica-filled Epoxy Nano-composites

Abstract

The dielectric properties of epoxy resin have been studied as a function of hydration. The epoxy was studied in an un-filled state, filled with 40 μm SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> particles, and filled with 50 nm SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> particles. The relative humidity was controlled by saturated salt solutions at ambient temperatures from 298-353 K. Measurements were made using dielectric spectroscopy over the frequency range 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> - 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> Hz. The hydration isotherm (i.e. the mass uptake of water) was established by measuring the mass as a function of relative humidity (RH). It was found that the nanocomposites absorb up to 60% more water than the unfilled and micro-filled epoxies. Dielectric spectroscopy shows different conduction and quasi- DC behaviours at very low frequencies (<10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> Hz) with activation energies dependent on the hydration and temperature. These observations have led to the development of a "water shell" model.