ELECTRIC-FIELD-INDUCED PATTERN-FORMATION IN COLLOIDAL DISPERSIONS

THE formation of patterned colloidal structures from dispersions of pa rticles has many potential uses in materials processing(1-3). Structur es such as chains of particles that form in the presence of electric o r magnetic fields are also central to the behaviour of electrorheologi cal fluids(4-6) and ferrofluids(7). Electrohydrodynamic effects in aqu eous suspensions have been described by Rhodes et al.(8). Here we show that such effects can be used to create structures within a non-aqueo us colloidal dispersion of dielectric particles, When the conductivity of a particle-rich spherical region (bolus) is higher than that of th e surrounding fluid, an electric field deforms the bolus into a prolat e ellipsoid. If the conductivities are reversed (by adding salt to the surrounding fluid, for example), a disk-like shape results. In this w ay, we form colloidal columns, disks and more complex structures. Once formed, these could be frozen in place by solidifying the fluid matri x by gelation or polymerization(9).