Supercritical Fluid

A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point where distinct liquid and gas phases do not exist. It can effuse through solids like a gas, and dissolve materials like a liquid. SCFs have the low viscosity of gas and the high density of a liquid, making it impossible to liquefy the matter using any amount of pressure. However, it is possible to go from a gas to a liquid without crossing the boundary between the vapor and liquid phase using a supercritical fluid just by lowering the temperature of the liquid (Observe phase diagram below).

 

 

Supercritical fluids have no surface tension because they are not subject to the vapor-liquid boundary so no molecules have the attraction to the interior of the liquid. The supercritical fluid of a substance can have very different properties than regular fluids. For instance, water that is supercritical differs from regular water in the fact that it is non-polar and acidic.

Supercritical fluids can occur in nature. For example, in places like underwater volcanoes, specifically those located deep beneath the ocean's surface, supercritical water is formed because of the immense pressure due to the depth and the intense heat from the vents of the volcano. This water can lead to the formation of crystals used in some jewelry.

 Supercritical fluids are useful in science today for purposes ranging from the extraction of floral fragrance from flowers and the process of creating decaffeinated coffee, to applications in food science and functional food ingredients, pharmaceuticals, cosmetics, polymers, powders, bio- and functional materials, nano-systems, natural products, biotechnology, fossil and biofuels, microelectronics, and environment