SCIENCE AT THE EDGE SEMINAR

	Friday, September 13, 2002
	11:30 a.m., Room 1400 Biomedical and Physical Sciences Building
	Refreshments at 11:15 a.m. in Room 1400A BPS Building

Title:
        Colloid Scale Engineering

Speaker:
	Eric W. Kaler
	Department of Chemical Engineering
	Colburn Laboratory
	University of Delaware
	Newark, DE  19716

Abstract:
A balance of repulsive and attractive molecular forces drives natural
assembly of molecules into complex organic and inorganic assemblies with
dimensions from nanometers to microns.  Our current nascent efforts to mimic
nature involve harnessing these same forces to produce synthetic assemblies
of the same colloidal-scale dimensions. In addition, alternating electric
fields easily move and guide colloidal particles, and so provide a
convenient way to guide assembly of functional structures between on-chip
conductive patterns using dielectrophoresis.  The range of possibilities for
engineering of these materials will be illustrated with three examples.
First, planar electrodes on either side of a large gap have been used for
the assembly of electrically switchable 2D colloidal crystals.  Single
domain, specifically oriented crystals of area >25 mm2 are obtained in less
than a second without prior templating.  Second, microscopic electronically
readable biosensors have been assembled from bio-functionalized latex
particles by combining dielectrophoresis with tuning of the colloidal
forces.  Finally dielectrophoresis is used to assemble metallic
nanoparticles into porous wires of micrometer diameter and millimeter
length.  These wires have good Ohmic conductance for both AC and DC
currents. The microwires form rudimentary self-assembled and self-repairing
"wet" circuits and are promising for application as sensors or in
bioelectronic circuits.