Phase diagrams of electric-field-induced aggregation in conducting colloidal suspensions

To develop a theory for electric-field-driven phase transitions in concentrated suspensions, we extended our microscopic theory [Phys. Rev. E 52, 1669, (1995); 54, 5428, (1996)] beyond the dilute regime. Based on the model of the Maxwell-Wagner interfacial polarization of colloids, our theory overcomes the limitations of Brillouin’s formula for the electric energy of conducting materials which is applicable only for negligibly small energy dissipation and slow time variations of the field. We found that the phase diagrams of “the particle concentration vs the electric field strength” for colloids are similar to the phase diagrams for the first-order phase separation in quenched conventional binary systems with a high-temperature miscibility gap. This explains why a variety of colloids exhibit similar field-induced aggregation patterns. Our theory provides a reasonable interpretation of the available experimental data on field-induced aggregation phenomena in electrorheological fluids and aqueous suspensions, whereas currently used theoretical models are in variance with many of the data. The theoretical results enable one to trace how the variations of the electrical properties of the constituent materials influence the topology of the suspension phase diagram and to evaluate the effects of the field strength and frequency on the particle aggregation.