Supercritical Water Videos
This video was kindly provided by Dr. Andy Shen and Prof. Bill Bassett of the Cornell University Department of Geological Sciences in the 1990's. It shows water going through its supercritical phase transition in a hydrothermal diamond anvil cell (see Bassett, W.A., Shen, A.H., Bucknum, M., and Chou, I-Ming (1993) A new diamond anvil cell for hydrothermal studies to 2.5 GPa and from -190 to 1200 C. Rev. Sci. Instrum., 64, 2340-2345). Initially a bubble of air is seen together with some water contained in the diamond anvil cell sample chamber. One is looking through one of the diamonds of the cell. The amount of water and free space in the form of air (the small quantity of low density air has a negligible effect on the water) has been carefully chosen so that the system will go supercritical along upon heating along the isochore (i.e. constant volume trajectory). At first boiling within the bubble is shown, but at 1 minute, 44 seconds the phase boundary between water vapor and liquid water simply disappears while the system is undergoing a supercritical phase transition. Phase separation into liquid + gaseous water is then shown at 2 minutes, 1 second, followed by criticality again. A brucite mineral crystal is in the upper right corner. Hydrothermal processes involving supercritical water are important to the formation of crystals of minerals within the earth and also are used for the fabrication of single crystals of materials such as quartz, used in every quartz watch. If you have trouble with the embedded video, here is a simple link to the mp4 version of the movie.
This much newer video from a Japanese scientist posted on YouTube reveals the details of the behavior in the various phases much better. The frame rate is increased 5x.
Supercritical Carbon Dioxide Video
This movie is of supercritical carbon dioxide. Initially the carbon dioxide is phase separated into liquid and gas. Liquid and gas can coexist because the pressure in the glass tube is above the pressure required for liquefaction. The heat gun is turned on, the liquid boils and expands, and then phase boundary (meniscus) between liquid and gas disappears. Next there is a second clip showing phase separation upon cooling the supercritical fluid. Critical opalescence is observed. It is easy to understand from this video why there is no surface tension in a "hybrid liquid/gas" supercritical fluid. If you have trouble with the embedded video, here is a simple link to the mp4 version of the movie.