Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 12: Confined Fluids
CPP 12.1: Talk
Tuesday, February 26, 2008, 11:00–11:15, C 230
Direct measurement of the critical Casimir force in a binary liquid using TIRM — •Christopher Hertlein, Laurent Helden, and Clemens Bechinger — 2. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany
A colloidal particle suspended in a binary liquid at the critical composition close to a substrate experiences a critical Casimir force upon approaching the critical temperature of decomposition Tc. We have measured interaction potentials for a single polystyrene particle suspended in a mixture of water and 2,6 -lutidine approaching Tc using Total Internal Reflection Microscopy (TIRM). TIRM is a technique for precise measurements of colloid - wall interaction potentials based on single particle evanescent wave light scattering. The measured interaction potentials display a clear contribution of the critical Casimir force which becomes stronger upon approaching Tc and is either attractive or repulsive depending on the preference for water or lutidine of substrate and/or particle. Theoretical calculations are in excellent agreement with experimental results. Switching the interaction from attraction to repulsion in situ is currently under investigation and could prove useful to control and fine-tune particle substrate potentials.