Dielectric Properties of Some Polymer-Powder Disperse Systems

Abstract

The dielectric properties of some polymer-powder disperse systems were investigated, using polyvinylacetate (PVAc), poly-methyl-meth-acrylate (PMMA) and poly-buthyl-methacrylate (PBMA) as the polymer components, and calcined non-active alumina, active alumina, silica gel and carbon black as the powder components.Bridge method, covering frequency range between 30cps and 5M cps, and temperature range between 10 and 160°C was used as the measuring apparatus, and the following results were obtained.(1) The dielectric constants of these disperse systems except the case of carbon black could be computed by Bruggeman's theory which assumed simple mixing. For carbon black powder, on the other hand, the measured dielectric constants were abnormally greater than that of the calculated values by Hanai's theoretical equation suggesting the existence of interfacial polarization. This phenomenon could be explained as the result of particle to particle chain formation.(2) Dielectric losses Δe obtained from Cole-Coles plots decreased with increase of the volume fraction of the fillers. The anomaly was also observed in the case of carbon black, indicating the occurence of interfacial polarization and the chain formation.(3) The width of the distribution curves of the relaxation time of these disperse systems became broader and the value of β in Cole-Cole's equation decreased remarkably, The tendencies appearing in the Δe and β values were more notable in the case of active fillers than in the case of non-active fillers.(4) Under constant temperature the characteristic frequency in which the dielectric losses gave its maximum values was observed to shift a little, no matter whether the absorption at segments in polymer chains were α or β, on the lower side of the frequency ordinates in the case of active fillers, and on the higher side in the case of non-active fillers, than when it was the case with unloaded polymers.From the results shown in (2), (3) and (4), are deducible the occurence of new relaxation mechanism corresponding to the particle-dipole interaction in these disperse systems.(5) The apparent activation energy calculated by the plots of log fmax vs. 1/T for both mechanisms of the α and β absorption curves was scarcely affected by the addition of filler powders.