Fundamental Interfacial Behavior of Confined Colloid-Polymer Systems

The phase equilibria of confined aqueous colloid-polymer systems are studied experimentally using fluorescence microscopy. The colloidal particles are fluorescent polystyrene spheres and the polymer is polyacrylamide, for which the ratio of the radius of gyration to the colloidal radius equals 0.73. The mixture is confined between a glass slide and a coverslip, such that the spacing between the glass plates varies between 3 - 6 microns.
The phase diagram is determined as a function of the colloidal and polymer concentrations. Liquid–liquid phase coexistence between a colloid-rich phase and a polymer-rich phase occurs at intermediate polymer concentrations, while liquid–solid phase coexistence between a polymer-rich liquid and a colloid-rich solid is observed at high polymer concentrations. The thickness of the interface between these  coexisting phases  is measured using image analysis. For liquid-liquid coexistence, the interfacial thickness is found to diverge as the critical point is approached. It is also observed that the colloid-rich solid and liquid domains coarsen mainly by Ostwald ripening.