A further investigation to mechanism of the electrorheological effect of waxy oils: Behaviors of charged particles under electric field

Abstract

Exposing waxy oils to an electric field may significantly improve their cold flowability. Our previous study has shown that interfacial polarization, i.e., charged particle accumulation on the wax particle surface, is the primary mechanism of the electrorheological behavior of waxy oils. However, the way that charged particles interact with wax particles under an electric field remains unknown. In this study, we found no viscosity and impedance change for two waxy crude oils after their exposure to a high-voltage electric field. However, the yield stresses were reduced obviously. We thus proposed that the collision of colloidal particles such as resins and asphaltenes with the wax particles could be an essential mechanism that the wax particle structure was weakened. To verify this hypothesis, a series of ad hoc experiments were carried out, i.e., by performing electrorheological tests on model waxy oils containing additives removable under an electric field, including electrically-neutral colloidal particles (Fe3O4), charged colloidal particles (resins), and oil-soluble electrolyte (C22H14CoO4), respectively, and demonstrated that upon application of a high-voltage electric field, charged particles in a waxy oil may move and thus collide with wax particles, and consequently adhere to the wax particle surface. The particle collision results in damage to the wax particle network, and the electrostatic repulsion arising from the adhesion of the charged particle on the wax particle diminishes attraction between wax particles. This study clarifies the process of interfacial polarization.