RELATIONSHIP BETWEEN PARTICLE-SIZE AND MAGNETORESISTANCE IN CARBON AEROGELS PREPARED UNDER DIFFERENT CATALYST CONDITIONS

Previous studies of the temperature dependence of the high-field positive magnetoresistance were carried out for carbon aerogels with a fixed [resorcinol]/[catalyst] (R/C) molar ratio of 200 but different mass densities. The present work focuses on the effect of the particle size on the transport properties of carbon aerogels of both high and low mass densities by varying the R/C ratio within the range of 50-300, the smaller R/C ratio corresponding to smaller particle size. Correlations of new results with SQUID and Raman findings identify the nanosize particles to be the localization sites for transport processes. The particle size can be estimated from the Coulomb-gap variable-range hopping model, which has been successful in explaining the low-temperature magnetoresistance data obtained for all carbon aerogels samples. The particle size thus extracted is consistent with transmission electron microscopy measurements on the carbon aerogels and is directly correlated with the R/C ratio. In polymeric carbon aerogels (R/C = 50), the average particle size becomes comparable with the width of the glassy-carbon-like ribbons within the particles, indeed blurring the distinction between particles and inter-particle links.