  In this Letter we consider a liquid mixture confined between two thermally
conducting walls subjected to a stationary temperature gradient. While in a
one-component liquid non-equilibrium fluctuation forces appear inside the
liquid layer only, non-equilibrium fluctuations in a mixture induce a
Casimir-like force on the walls. The physical reason is that the temperature
gradient induces large concentration fluctuations through the Soret effect.
Unlike temperature fluctuations, non-equilibrium concentration fluctuations are
also present near a perfectly thermally conducting wall. The magnitude of the
fluctuation-induced Casimir force is proportional to the square of the Soret
coefficient and is related to the concentration dependence of the heat and
volume of mixing.
