Reversible phase transition of colloids in a binary liquid solvent.

We report fluid-fluid and fluid-solid phase transitions of charge-stabilized polystyrene particles suspended in a binary liquid mixture of 3-methylpyridine and water. These thermally reversible phase transitions occur in the homogeneous phase of the binary liquid mixture below the coexistence temperature of the two liquids. Close density matching of the particles and the solvent allows us to follow the phase behavior until complete coexistence of macroscopic phases with temperature as the control parameter. We use small angle x-ray scattering to characterize these phases as colloidal gas, liquid, fcc crystal, and glass.