Critical Nanoaggregate Concentration of Asphaltenes by Direct-Current (DC) Electrical Conductivity†

The critical nanoaggregate concentration (CNAC) of asphaltenes in toluene has been studied by a variety of methods recently. Here, we explore low-frequency electrical impedance measurements to detect and quantify nanoaggregate formation of asphaltenes. The Nyquist and Bode plots confirm the frequency range necessary for the dominance of (organic) ion conduction as opposed to reactive impedance. Impedance measurements are made as a function of the asphaltene concentration in toluene. We perform ionic conduction measurements at low frequency to avoid electrode polarization effects and then extrapolate to obtain direct-current (DC) conductivity. In a plot of DC conductivity versus asphaltene concentration, we see a clear break between two linear regions that is attributed to nanoaggregate formation. Very close agreement with high-Q ultrasonic measurements is shown for two petroleum asphaltenes with different CNACs. In addition, this work is shown to be consistent with previous alternating-current (AC) conduc...