Monday, July 21, 20083:00 PM - 4:00 PMCNLS Conference Room (TA-3, Bldg 1690)|
Direct measurement of critical Casimir forces
Clemens BechingerUniversität Stuttgart, Physikalisches Institut
Similar to electromagnetic vacuum fluctuations
which can induce long-ranged interactions between
uncharged, conducting surfaces, a related effect was predicted almost 30 years ago to occur in confined binary mixtures close to their critical point. This so-called critical Casimir effect has attracted considerable attention because it can strongly modify the interaction potential of colloidal particles immersed in a binary fluid.
We present the first direct measurement of such
critical Casimir forces between a colloidal
particle and a flat surface in a water – 2,6-lutidine mixture. With total internal
reflection microscopy (TIRM) which is capable to
resolve forces down to 5fN, we obtain distance
resolved particle-wall interaction profiles. Upon
approaching the critical point we observe
long-ranged interactions which are attractive or
repulsive depending on the specific boundary
conditions of the walls. This behavior is in good
agreement with recent theoretical predictions.
C. Hertlein, L. Helden, A. Gambassi, S. Dietrich,
and C. Bechinger, Direct measurement of critical
Casimir forces, Nature 451, 172 (2008).
Host: Charles Reichhardt, T-13