DIELECTRIC STUDIES OF MINERAL-FILLED EPOXY

Dielectric studies in epoxy and epoxy composites, containing different volume fractions of three different dielectric fillers, have been per formed using the impedance bridge method for the high frequency region , 10(2) to 10(5) Hz, and the d.c. transient current method for the low frequency region, 10(-4) to 10(-1) Hz. It has been observed that, in the high frequency region, the dielectric constants of the epoxy compo sites increased with the addition of the dielectric filler and with th e increase of the dielectric constant of the filler. The intensity of the beta-relaxation was reduced for the composites compared to an equa l volume of epoxy, owing to the decrease in the concentration of the d iester segments in the composites. From the low frequency data, the ep oxy and epoxy composites behaved more debye-like with increasing tempe rature. Also, the dielectric loss factor increased, but the thermal ac tivation energy value to relaxation decreased two to four times in goi ng from the unfilled to filled materials, which was thought to be attr ibuted to Maxwell-Wagner buildup of interfacial charges at the epoxy/f illers interfaces.