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[摘要]：Direct current (DC) and alternating current (AC) (120 and 1000 Hz) conductivity and AC dielectric properties of solid precipitated asphaltenes have been studied at temperatures of 5-105 degrees C. The temperature dependencies revealed the presence of a structural transition, ascribed to changes in the predominant type of intermolecular bonding. Apparently, at solid surfaces, this transition occurs at absolute temperatures about 20% lower than in the solid bulk. Analysis of conductivity mechanisms is supplemented by a comparison of UV-vis-NIR absorption spectra for solid asphaltenes and their solution in toluene. It is concluded that, in solid asphaltenes, surface conductivity is always predominant over the bulk one. The major transport mechanism of charge carriers at asphaltene surfaces appears to be unidirectional electron hopping between spatially close shallow localized traps. The dielectric constant of solid asphaltenes below 35-40 degrees C was found to be both frequency-and temperature-independent and was evaluated as epsilon = 4.3 - 5.4. |
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