Critical Casimir forces in colloidal suspensions

Some time ago, Fisher and de Gennes pointed out that long-ranged correlations in a fluid close to its critical point T-c cause distinct effective forces between immersed colloidal particles which can even lead to flocculation [C. R. Acad. Sc. Paris B 287:207 (1978)]. Here we calculate such forces between pairs of spherical particles as function of both relevant thermodynamic variables, i.e., the reduced temperature t = ( T - T-c)/T-c and the field h conjugate to the order parameter. This provides the basis for specific predictions concerning the phase behavior of a suspension of colloidal particles in a near-critical solvent.