- Surfactants from micelles at well-defined concentrations when immersed in water. The first formed aggregates are approximately spherical in shape. As the concentration of surfactant is increased or, upon the addition of salt or other additives, a transformation ofthe micellar shape often takes place. The structure/size and other properties of such micelles have been a rather intense field of study for many years. On the basis of rheology, scattering, and different NMR methods, it seems clear that many of these systems are composed of long threadlike micelles, often called" wormlike" micelles, which are entangled. In effect, their properties are similar to polymers in the semidilute concentration regime, the main difference being that the surfactant micelles have a weight distribution which is a true equilibrium property (hence they are often referred to as" living polymers").