The interface in demixed colloid-polymer systems: wetting, waves and droplets

Phase transitions in colloid-polymer mixtures have attracted a large amount of attention over the last 20 years (W. C. K. Poon, , 2002, , R859; R. Tuinier, J. Rieger and C. G. de Kruif, , 2003, , 1). By comparison, the interfacial tension between the coexisting phases has received little attention. Here, we show that the ultralow interfacial tension in fluid-fluid demixed colloid-polymer systems, which is roughly one million times smaller than in ordinary liquids, manifests itself in a wide variety of interface characteristics and processes. Discussed are the interfacial wetting behaviour close to a hard wall, the thermal capillary waves at the free interface and the process of droplet coalescence and breakup. These subjects can be studied in a single experiment by combining modern soft matter chemistry and laser scanning confocal microscopy. This combination allows a further exploration of a broad range of interface issues.