EVOLUTION OF ION MOBILITY IN CURED EPOXY-AMINE SYSTEM AS DETERMINED BY TIME-OF-FLIGHT METHOD

The concept of the time-of-flight (TOF) method for the determination o f ionic carriers' mobility is presented. This method is used for the m odel system, the properties of which (including viscosity) change with time: the isothermally cured epoxy-amine system. It is demonstrated t hat the form of the TOF current signals depend on the material of the electrodes. The Cu, Ag, Al, and Au electrodes were tested; of these, t he Cu and Au electrodes have yielded the most distinct TOF signals and therefore were chosen for further experiments. The investigated sampl es were placed between parallel electrodes with guard rings distanced with polyethylene terephthalate (PET) films of different thickness (0. 02-0.2 mm). According to the predictions, it was found that the TOF of the ionic carriers increases with an increase of the distance between the electrodes (for constant electric field) and decreases with an in crease of the electric field (for constant distance). The series of me asurements performed for the well-known epoxy resin system diglycidyle ther of bisphenol A with no-4,4'-dimethyl-3,3'-dimethyldicyclohexylmet hane, isothermally cured at different temperatures, have confirmed tha t in a course of the curing, below the gelation, the conductivity decr eases following the decrease of the ionic mobility due to the viscosit y increase during the reaction. However, with an advancement of reacti on, deviations from that linear relationship are observed. (C) 1997 Jo hn Wiley & Sons, Inc.