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Simple Fabrication of Metallic Colloidal Doublets Having Electrical Connectivity

Joseph J. McDermott, Chemical Engineering, The Pennsylvania State University, 175 Fenske Lab, The Pensylvania State University, University Park, PA 16802 and Darrell Velegol, Department of Chemical Engineering, The Pennsylvania State University, University Park, PA 16802.

Metallic colloidal doublets of gold-gold, silver-silver, and gold-silver, shown to be electrically connected, were fabricated using the salting out / quenching technique. Micron sized gold and silver colloids were first formed by the aggregation of nanoparticles in the presence of steric stabilizers. Doublets of these particles were then fabricated with greater than 20% yield by the salting out / quenching technique, which relies on controlling aggregation by temporally controlling the interparticle forces. At first the ionic strength is made high (~0.5 M) to allow for quick aggregation of singlets into doublets, and then the ionic strength is made lower (e.g., by adding DI water) to quench the aggregation process. The mechanical stability of the doublets was investigated both under normal conditions and under sonication, and it was shown that the homodoublets of gold-gold and silver-silver were very stable mechanically, while the gold-silver doublets were slightly less stable under sonication. Electrical connectivity of the gold-silver heterodoublets was found by observing the behavior of the doublets in 3% hydrogen peroxide solution. The gold-silver heterodoublets showed autoeletrophoretic movement, consistent with electrical connectivity across the gold-silver interface. The formation of these doublets reveals robustness in the salting out / quenching technique, and the electrical connectivity provides possibilities for numerous applications.