A micelle is the self assembled sphere formed from surfactants in a hydrophilic liquid such as water. It is formed when surfactant hydrocarbons that have a hydrophilic charged head group and a long hydrophobic tail aggregate. The hydrophobic tails are attracted to each other and try to get out of their hydrophilic environment by bunching up. This leaves the hydrophobic heads pointing outwards where they are content in their environment. Micelles are often spherical, however they can be elliptical as well. Concentration, molecular structure, ionic strength, temperature, and pH, among other variables, all contribute to the geometry of the micelle formed.
Micelles have various applications, that are similar to the applications of surfactants. In biology, they are essential for dissolving any fats, or fat soluble vitamins in the body. Also, they are used in detergents to help cut away grease, again using their dissolving properties.
Reverse micelles are the opposite of typical micelles - they form in a hydrophobic environment. These micelles have the hydrophilic heads aggregating in the center of the sphere, with the hydrophobic tailes pointing outwards. These micelle are used to form miniature test tubes because they create a nanoscale hydrophilic environment at their center where reactions can occur. One application of these is the formation of quantum dots at the center of these reverse micelles.