Contact-Free Templating of 3-D Colloidal Structures Using Spatially Nonuniform AC Electric Fields

The formation of ordered and regularly shaped structures of colloidal particles with the aid of spatially non-uniform electric fields is a modern research area of great interest. This work demonstrates how alternating current (AC) electrokinetic effects (dielectrophoresis, electroosmosis) can serve as active and contact-free templates that drive the assembly of colloidal spheres into three-dimensional structures of various shapes and sizes in aqueous or non-aqueous liquids. The concept is demonstrated here with a set of quadrupolar planar microelectrodes having tip-to-tip separation of 100 microns. By controlling the electric field intensity, suspending fluid properties and mode of power delivery to the microelectrodes, assembly of silica microspheres (d=2.0 microns) into 3-D objects of square, circular, diamond and various asymmetric shapes of tens of microns in size can reproducibly be accomplished. Near-refractive index matching of suspensions encouraged ordered-type structures. All assemblies showed s...