  From experimental studies it is well-known that colloidal particles suspended
in a near-critical binary solvent exhibit interesting aggregation phenomena,
often associated with colloidal phase transitions, and assumed to be driven by
long-ranged solvent mediated (SM) interactions (critical Casimir forces), set
by the (diverging) correlation length of the solvent. We present the first
simulation and theoretical study of an explicit model of a ternary mixture that
mimics this situation. Both the effective SM pair interactions and the full
ternary phase diagram are determined for Brownian discs suspended in an
explicit two-dimensional supercritical binary liquid mixture. Gas-liquid and
fluid-solid transitions are observed in a region that extends well-away from
criticality of the solvent reservoir. We discuss to what extent an effective
pair-potential description can account for the phase behavior we observe. Our
study provides a fresh perspective on how critical fluctuations of the solvent
might influence colloidal self-assembly.
