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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 9: POSTER: Colloids and Nanoparticles
CPP 9.12: Poster
Monday, March 26, 2007, 16:00–18:00, Poster B
Employing TIRM to measure critical casimir forces in a binary liquid — •Laurent Helden, Christopher Hertlein, and Clemens Bechinger — 2. Physikalisches Institut, Pfaffenwaldring 57, D-70550 Stuttgart
The technique of total internal reflection microscopy (TIRM) is capable to measure interactions of a spherical colloidal particle close to planar wall. Forces as small as 5 fN can be detected, thus TIRM can be employed to directly measure extremely weak interactions like critical casimir forces.
Due to concentration fluctuations 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 directly measured interaction potentials for a polystyrene particle suspended in a mixture of water and 2,6 -lutidine approaching Tc. In agreement with theoretical predictions strongly temperature dependent forces were detected. The sign of the forces depends on the wetting properties of probe particle and substrate.