(420g) Patterning Simple Geometries with Colloids Using a Scanning Laser

Rapid Electrokinetic Patterning (REP) is a relatively new technique used for gathering, sorting, and manipulating colloids at an electrode surface.  REP requires an AC electric field to trap particles at a planar electrode surface, and also requires a heat source to generate a vortex to manipulate trapped particles.  The heat source used was an infrared laser, which was absorbed by one of the Indium Tin Oxide (ITO) electrode surfaces.  The heat absorbed by the surface transfered to the medium, creating a gradient in electrical properties.  The AC field acted on this gradient to produce a net force, inducing a vortex.  The vortex creates a drag force on the particles which can be used to sort the particles.
The ability to collect colloids, move them, and control the geometry of the captured group of colloidal particles was explored.  One- and two- micron polystyrene particles were used in experimentation.  It is shown that simple geometries, such as dots and straight lines, can be formed and controlled.  The time required to gather particles is explored, as well as the maximum moving speed of the geometries explored.  The minimum angle allowed of intersecting geometry is explored, as well as closed geometry, such as elliptical shapes.  Also explored are moving geometries that are made to intersect with each other.