Observation of colloidal crystals with the cesium chloride structure

Binary mixtures of hard sphere-like colloidal particles, of the same size but different polymer composition, when suspended in some liquids phase separate and form crystals with the Cesium Chloride structure. We attribute this behavior to a cross-attraction between particles of the different species. In other suspending liquids this apparent cross-attraction is absent; hard sphere-like behavior is observed with the expected randomly stacked close packed crystal structure with no positional correlation of the two particle types.