Critical Casimir Forces

The geometrical confinement of liquid mixtures close to their critical point gives rise to so-called critical Casimir forces. They are due to local fluctuations in the concentration of the mixture, which diverge close to the critical point and thus lead to long-ranged effective interactions. Critical Casimir forces are characterized by a strong temperature dependence but also by a high sensitivity for the corresponding surface properties of the confining walls. This allows one not only to vary the amplitude but even to reverse the sign of critical Casimir forces.