Maxwell–Wagner–Silars relaxations due to glass occlusions in a thermoset composite

Abstract

Maxwell–Wagner–Silars (MWS) dielectric relaxations have been studied in thermoset composites made with hollow glass microspheres and reinforced with aramid fiber. Over the temperature range reported (140–230 °C) the glass microspheres show a conductivity of 10−10–10−5 (Ω cm)−1 so that MWS loss peaks fall in the 102–105 Hz frequency range. The apparent activation energy for the relaxation is about 20 kcal/mole. The observed MWS relaxation times depend only on temperature and not on volume fraction of microspheres as predicted by MWS theory. Also, the enhancement of activation energy for the relaxation over the activation energy for conduction of the glass seems to be explainable from the standpoint of the frequency and temperature dependence of the glass dielectric constant.

Interfacial behavior of epichlorohydrin–ethyleneoxide–allylglycidyl ether/fluorinated carbon black observed from mechanical and dielectrical properties

“…The values of activation energy of MWS relaxation, E a MWS , calculated from an Arrhenius equation are listed in Table III for three samples of CHR composites. It has been suggested that E a MWS values do not depend on filler content 18, 19. We point out that the E a MWS decreases with increasing fluorine content on the CB surface.…”

“…It has been suggested that E a MWS values do not depend on filler content. 18,19 We point out that the E a MWS decreases with increasing fluorine content on the CB surface. The reduction of the ␥ d by fluorine modification promotes the weak interaction between CHR and CB particles.…”

“…Therefore many researchers have regarded the peak composed of MWS and α‐relaxation processes as the peak of MWS relaxation process. The double peak can be seen in the frequency dispersion of dissipation factor tan δ as shown in Figure 4(A), where it is shown that the peak in the higher‐frequency region (∼ 100 kHz) is attributed to the α‐relaxation process, and the peak in the frequency region ranging on the order of about 1 kHz is attributed to the MWS relaxation process 17–20, 26. The information derived from Figure 4(A) is helpful for strictly estimating the molecular mobility on the carbon black surface.…”

“…The activation energy calculated from the MWS relaxation frequency for the composites made of polymer matrix and more conductive filler depends not only on the respective values of the conductivities and permittivities but also on the shape and size of the fillers 16, 17. However, the relationship between the MWS relaxation and the mobility of polymer chain on filler surface is not yet clear, given that it is very difficult to separate the peak of MWS relaxation and α‐relaxation of the polymer matrix 18–20…”

Molecular dynamics of copolyester/clay nanocomposites as investigated by viscoelastic and dielectric analysis

“…The obtained values of the activation energy are about 0.9 eV. It has been reported in the literature that E A‐MWS values do not change much with filler content 39, 40…”