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

To develop a theory for electric-field-driven phase transitions in concentr ated 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 overco mes the limitations of Brillouin's formula for the electric energy of condu cting materials which is applicable only for negligibly small energy dissip ation and slow time variations of the field. We found that the phase diagra ms of "the particle concentration vs the electric field strength" for collo ids 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 t he available experimental data on field-induced aggregation phenomena in el ectrorheological fluids and aqueous suspensions, whereas currently used the oretical models are in variance with many of the data. The theoretical resu lts enable one to trace how the variations of the electrical properties of the constituent materials influence the topology of the suspension phase di agram and to evaluate the effects of the field strength and frequency on th e particle aggregation. [S1063-651X(99)14208-9].