In-situMeasurement of the Properties of Curing Systems with Microdielectrometry

Abstract

This paper addresses the in-situ measurement of various properties of curing systems with a particular dielectric method called Microdielectrometry. We have used integrated circuit technology to develop a miniaturized dielectric probe that combines small size with built-in amplification to achieve sensitivity at frequencies as low as 1 Hz. The device combines a planar interdigitated electrode structure with a pair of matched field-effect transistors. Calibration is based entirely on the details of the electrode geometry, and thus is stable with respect to temperature variations, and is reproducible from device to device. Generally, what is measured is the frequency dependent dielectric permittivity (ϵ) and dielectric loss factor (ϵ) in the frequency range 1–1000 Hz. In this paper, the results of isothermal cures of the amine-epoxy system DGEBA-MPDA are presented, and are shown to provide a measurement of a low-frequency dielectric relaxation time which can be correlated with bulk viscosity prior to gelation. We also present a study of the effects of PGE diluent on the DGEBA-DDS system, both during isothermal cures at 140°C, and in post-cure ramped temperature studies. It is shown that as little as 5% diluent produces observable changes in the low-frequency dielectric properties, and that frequencies below 10 Hz are more sensitive than higher frequencies to the effects of diluent on the dominant low-frequency dielectric relaxation associated with the glass transition.