# "The universal force of critical fluctuations: Casimir, wetting, colloids and all that."

PHYSICS DEPARTMENT COLLOQUIUM

### The universal force of critical fluctuations:

Casimir, wetting, colloids and all that.

** Andrea Gambassi **
SISSA-International School for Advanced Studies and INFN, Trieste (Italy)

In 1948, Hendrik Casimir predicted that two uncharged conducting surfaces in vacuum attract

each other due to the quantum fluctuations of the electromagnetic field which are spatially

confined by these surfaces. The classical analogue of this effect originates from the confinement

of thermal fluctuations in fluids near continuous phase transitions, such as the demixing

of a mixture of two liquids or the normal-superfluid transition in 4He, and it was first

investigated theoretically by Michael Fisher and Pierre-Gilles de Gennes in 1978.

Early indirect experimental evidence of the force of these fluctuations - known as critical

Casimir force - were provided by detailed studies of complete wetting films. Its first direct

measurement at the sub-micrometer scale, instead, was done only in 2008 by monitoring the

Brownian motion of a colloidal particle close to a surface, both immersed in a near-critical

liquid mixture. I will present recent advances in the theoretical and experimental study

of the universal properties of this novel fluctuation-induced force, discussing in particular

its non-equilibrium behavior and possible relevant applications to soft matter systems.

**Date: ** November 27, 2013 (Wednesday)

**Time: ** 16:00-17:00

**Place: ** EE01