Field- and concentration-dependence of electrostatics in non-polar colloidal asphaltene suspensions

Electrostatic stabilization has recently been found to be an important factor in non-polar colloidal asphaltene suspensions. However, the nature of charging in asphaltene systems may be quite different than in other non-polar colloid systems. For instance, the origin of charging in asphaltene colloids arises from both positive and negative charges native to the asphaltenes. In part due to this bimodality of surface charge, some dispersants are shown to stabilize asphaltene colloids at concentrations below their cmc. This effect does not arise from ionic effects of the dispersant, but rather from preferential dispersant adsorption onto charged sites on the colloidal asphaltene surface. Due to the long-range nature of electrostatics in non-polar systems, electrophoretic mobility can depend on both electric-field and particle volume fraction. We investigate the field- and concentration- dependence of electrophoretic mobility in non-polar colloidal asphaltene suspensions. Our results suggest that colloidal asphaltene suspensions stabilized by non-ionic dispersants can exhibit large screening lengths even in the presence of dispersant micelles. Due in part to the large screening length, a decrease in electrophoretic mobility can occur even at low colloidal particle concentrations.