Properties, main applications and perspectives of worm micelles.

This tutorial review deals with one of the most remarkable forms of surfactant aggregates, described as having a flexible, elongated cylindrical shape. Three structural scale lengths are pertinent to the flexibility and mobility of worm micelles: the cross-sectional radius, r(cs), the overall (contour) length, L, and the persistence length, l(p). The diversity of l(p) values in amphiphilic systems is demonstrated as well as the relation between L and l(p). The review also discusses the viscoelasticity of worm micelles and the relaxation mechanisms underlying this dominant property. Many aspects of viscoelasticity--such as non-linearity, shear banding, flow-induced phase transition, rheochaos--are only shortly described. The prevailing application of worm micelles, namely as fracture fluids and drag reducing agents are discussed in detail, stressing the effect of variations in the surfactant molecular structure on the efficacy of worm micelles. The vague possibility of using "smart" worm micelles in the foreseeable future is tersely outlined.