Thursday, November 11, 2010: 12:50 PM
Topaz Room (Hilton)
Controlling the kinetics of colloidal aggregation is an easy and effective method of fabricating colloidal assemblies. A new controlled assembly technique, 'Quenched Electrostatic Assembly' (QEA) has been developed that allows for the assembly of two- and three-component colloidal trimers in a specific order, but with random orientation. The QEA technique introduces oppositely charged larger core and smaller satellite particles into solution together. The satellites begin to electrostatically adhere to the core particles. After the desired number of satellites has adhered, the aggregation is quenched by the addition of polymeric nanoparticles with the same charge as the satellites. These nanoparticles quickly coat the remaining bare regions of each core, effectively blocking further satellites from adhering. Fusing the nanoparticle coating by heating the assembled trimers above the glass transition of the nanoparticles greatly increases the mechanical stability of the assemblies. This technique is used to produce trimers of three different colloidal particles that are mechanically and thermodynamically stable, with a maximum theoretical yield of 15%. Quenched Electrostatic Assembly has been used to form trimers out of particles of varying sizes and materials, including out of gold and silver microparticles. By forming trimers with a semiconducting core and gold and silver satellites, we fabricate complex colloidal motors that move in hydrogen peroxide solution through the mechanism of autoelectrophoresis. The movement of these trimers can be controlled by exposing the semiconducting core to light with energy equal to or more than the semiconductor band gap, changing the conductivity of the core particle.