Jh. Kaiser, MICROWAVE EVALUATION OF THE CONDUCTIVE FILLER PARTICLES OF CARBON BLACK-RUBBER COMPOSITES, Applied physics. A, Solids and surfaces, 56(4), 1993, pp. 299-302
Samples of carbon black loaded nitrile rubber are measured at microwav
e frequencies (waveguide transmission and reflection). The observed di
electric relaxation is interpreted using a two phase effective medium
model (Bottcher formula). The two phases are identified with free rubb
er as insulating matrix and a conductive filler of a priori unknown pa
rameters (volume fraction, permittivity, conductivity). Supported by S
EM and dc measurements the results allow to associate the filler phase
with adsorbate covered carbon black. In this way the bulk conductivit
y of carbon black loaded rubber can be explained by (statistical) perc
olation, which has been not possible taking pure carbon black particle
s as the percolating elements. Because the effective conductivity of t
he filler particles deduced from the microwave measurements characteri
zes mainly the particles' surface it is supposed that the adsorbate ma
y become conductive by the chemical and physical interactions of polym
er and carbon black during the preparation of the composite. Reference
is made to the doping of rubber resulting in conductivities of the sa
me order of magnitude.