Solid loading effects on the assembly of alumina particles in aqueous suspensions due to the dielectrophoretic forces

Current work in situ investigated the mechanisms of the interparticle interactions that evolve in dilute aqueous alumina suspensions subjected to alternating current (AC) electric field and the effects of solid loading of suspensions. The interactions were investigated for alumina suspension compositions in the 0.005‒0.04 vol.% solid loading range. Field-induced interactions evolved via particle motion and dynamic assembly, chain formation parallel to the direction of the applied field and chain growth, chain cross-linking, and chain thickening. The evolution time of each of those events was rapidly accelerated with solid loading. While chain cross-linking was negligible in low solid loading suspensions, a dense network of thick chains evolved in higher solid loading suspensions. An important takeaway was that with the increasing solid loading, individual chains could only grow independently up to a comparable length in most of the suspensions but at a rapidly decreasing field duration. Solid loading effects originated due to the decrease in the interparticle distances and increase in the number of particles in a given volume with solid loading, increasing attractive dielectrophoretic (DEP) interaction forces and accelerating the interactions. Insights were shed into the role of AC field in the freeze-casting of ceramics from concentrated suspensions.