Structure Evolution of Ferrofluid Emulsions

Abstract

The evolution of field-induced structure in a colloidal system through dipole interactions has recently been studied in cells with little or no confinement. For example, one study [1] was carried out in an electrorheological (ER) fluids. A dipole interaction aligns the particles into chains, and different chains further coalesce to form columns. The coarsening is believed to be due to thermal fluctuations along chains. The theory [1] has predicted that for an infinitely long chains the coarsening due to thermal fluctuation should follow a power law of the form: d ~ t ^5/9. The experimental result for a cell thickness of 0.7 mm shows that the chain coarsening varies in time in accordance with the power law d ~ t ^0.4, where d is a characteristic length of the structure. This experiment has considered the effect of cell thickness or width along the field direction to be essentially infinite due to image dipoles formed at the boundaries. Therefore, in that case the system is unconfined.