Dielectric and mechanical relaxation in epoxy systems with molecules of differing topology

Two epoxy systems with molecules having different topologies and functional ities, i.e. bifunctional linear and trifunctional star-like molecules, are characterized by means of both dielectric and mechanical spectroscopy metho ds in order to detect segmental and molecular relaxation rates as functions of temperature. The dielectric method is also used to determine the ionic conductivity effects in both systems. An effect of pressure at a constant t emperature on the segmental relaxation times and on the conductivity is als o investigated. We also examined coupling between the de-conductivity relax ation process and alpha -relaxation process. As a result it was found that the dependence of the de-conductivity relaxation time on the alpha -relaxat ion time can be described by means of the fractional Debye-Stokes-Einstein power-law relation. Like for our previous high-pressure results on other gr ass formers, it turns out that the pressure dependence of the alpha -relaxa tion time systematically deviates from the exponential form on approaching the glassy state.