Alignment of particles by an electric field

Particles in a photopolymerizable liquid were aligned by an electric field. Polymerization of the liquid allowed the composite to be sectioned or fractured on various planes and the aligned structures and their sequence of formation to be studied. Three populations of glass spheres (narrow size distribution, 25 μm average diameter; broad size distribution, 11 μm average diameter; and broad size distribution, 18 μm average diameter) and one population of barium titanate particles (0.2 μm average diameter that typically formed 1.2 μm average diameter aggregates) were used. For each of the systems studied (containing either 10 vol % glass spheres or 4 vol % barium titanate), the structure formed in three distinct stages. String formation occurred first, by the longitudinal attraction of particles, ribbon formation followed, by the lateral attraction of neighboring strings, and column formation (coarsening) occurred at long times under the field, by the collapse of the ribbons. The growth of the aligned particle strings was measured, and the result was adequately described by a simple model. The measured flocculation times, for pairs of particles to coalesce, were shorter than predicted, probably because of the slight conductivity of the fluid.