Colloidal Electrostatic Interactions Near a Conducting Surface

Marco Polin [1], David G. Grier [1] and Yilong Han [2]
[1] Center for Soft Matter Research, New York University, 4 Washington Pl. New York, NY 10003
[2] Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd St., Philadelphia, PA 19104

Date: September 10, 2007

Abstract:

Like-charged colloidal spheres dispersed in deionized water are supposed to repel each other. Instead, artifact-corrected video microscopy measurements reveal an anomalous long-ranged like-charge attraction in the interparticle pair potential when the spheres are confined to a layer by even a single charged glass surface. These attractions can be masked by electrostatic repulsions at low ionic strengths. Coating the bounding surfaces with a conducting gold layer suppresses the attraction. These observations suggest a possible mechanism for the anomalous confinement-induced attractions.