Electric Conductance in Liquid Hydrocarbons

The spatial variations of charge density in current carrying unsaturated and saturated hydrocarbons have been determined by means of a probe technique between 20 and 65C for electric stresses of 50 to 300 volts and electrode separations of up to 1 cm. The charge distributions observed with unsaturated hydrocarbons were found to be quite different from those obtained for saturated hydrocarbons both in shape and time dependence. With all unsaturated hydrocarbons tested, an excess negative charge was found in the vicinity of the anode. For these materials, a total space charge was found which depended inversely on electrode separation whereas it was essentially nil for aliphatic hydrocarbons. The voltage-current characteristics of these materials were also determined for electric fields ranging from 1 to 106 volts/cm using dynamic as well as steady-state methods to elucidate the time dependence of the conduction process. The results of these experiments have been interpreted to suggest two different conduction mechanisms for the two classes of compounds. In the case of saturated hydrocarbons, electrical conduction has been attributed to the presence of polar impurities or trapped electrons which originate both at the electrode surface and in the bulk of the liquid. The conduction of electricity in unsaturated, aromatic hydrocarbons was attributed to the hopping of electrons. The observed voltage-current characteristics were found to be inconsistent with the predictions obtained from classical theories.