Simultaneous monitoring of viscoelastic and dielectric properties of curing epoxy resins using a vibrating electrode

Abstract

Both dielectric and mechanical dynamic analysis can characterize the curing of epoxy resins. As the reproducibility of this process is poor, data from separate measurements cannot be compared. To allow for a simultaneous measurement of frequency-dependent viscoelastic (0.5–8 kHz) and dielectric (50–800kHz) properties, a vibrating electrode is used. The curing measurements of four different epoxy-amine systems show a frequency-dependent drop in both the dielectric and compliance real parts. Higher frequencies are sensitive to the relaxation of smaller molecules, hence, the step due to vitrification occurs first at higher frequencies. Accompanied by a loss maximum the dielectric step shifts down over four decades to a lower frequency region and appears eventually in the mechanical spectrum. The simultaneous investigation reveals that the dielectric and the longitudinal compliance function have almost the same frequency dependent reaction kinetic behavior. The mechanical time behavior can be extrapolated in the frequency domain by a power law to obtain the dielectric time parameters and vice versa.