8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.165Trapping colloids via critical Casimir forcesMatthias Tröndle, 1 Andrea Gambassi, 2 Ludger Harnau, 1 and Siegfried Dietrich 11 Max Planck Institute for Intelligent Systems and University of Stuttgart, Heisenbergstr. 3,70569, Stuttgart, Germany2 SISSA - International School for Advanced Studies and INFN, Trieste, ItalyColloids immersed in a (near-) critical binary liquid mixture are subject to effective critical Casimirforces mediated by the solvent. Since the direction of these forces depends on the adsorption preferencesat the surfaces, colloids opposite to substrates patterned with stripes of different chemicalboundary conditions experience normal and lateral critical Casimir forces. Upon approaching thecritical demixing point of the solvent, this generates laterally confining potentials for the colloids.The strength of these potentials is (reversibly) tunable by minute temperature changes. Experimentalmeasurements of such colloid-trapping potentials agree with the corresponding theoreticalpredictions. A suitable choice of substrate patterns may even lead to levitation of colloids at a stabledistance above the substrate due to the critical Casimir effect. This provides a new mechanismfor controlling colloids as model systems, opening encouraging perspectives for applications.165