ELECTROPHYSICAL PROPERTIES OF COMPOSITES BASED ON THE EPOXY RESIN AND EXPANDED GRAPHITE.

The composites of epoxy resin-expanded graphite(EG)-vermiculite and epoxy resin-expanded graphite-perlite were obtained and their electrophysical properties were analysed at low frequencies and in the microwave range. High values (> 30) of real and imaginary components of the complex permittivity for both systems were achieved with a content of EG of less than 2 wt. %. The values of the percolation threshold and critical index of systems were defined: for a system with vermiculite the percolation transition (φc = 0.0018); and for a system with perlite (φc =0.0039). The method of impedance spectroscopy (10-2–106 Hz) shows that for all investigated composites there is no dependence of electrical conductivity to frequency, but up to a value of 103 Hz, indicating a low level of ionic conductivity. It was found that the difference in electrophysical characteristics of two systems with the same content of the expanded graphite arises due to the nature of the surface of the dielectric components. The best indicators, namely, the lower percolation threshold and the achievement of maximum electrical conductivity values at lower EG, are in the system with vermiculite. It is due to the hydrophobic properties of the surface the filler particles, as well as the effect of the flow of a dielectric particle of vermiculite by a suspension of an epoxy resin-EG, while the particles perlite is impregnated with it. Changing the content of such dielectric ingredients allows us to expand the functionality of composites when used for shielding from electromagnetic fields. [ABSTRACT FROM AUTHOR]