Shape and Structure of Micelles

Debye and Anacker proposed that micelles are rod-shaped rather than spherical or disklike. The cross section of such a rod would be circular, with the polar heads of the detergent lying on the periphery and the hydrocarbon tails filling the interior. The ends of the rod would almost certainly have to be rounded and polar. In 1956, Hartley s spherical micelle model was established by Reich from the viewpoint of entropy, and the spherical form is now generally accepted as approximating the actual structure (Fig. 4.3). 

Micelles of ionic surfactants are aggregates composed of a compressive core surrounded by a less compressive surface structure/ and with a rather fluid environment (of viscosity 8-17 cP for solubilized nitrobenzene in SDS and cetyltrimethylammonium bromide micelles). Copper ions attached to micelles have essentially the same hydration shell near the micellar surface as in the bulk phase, and do not penetrate into the nonpolar part of the micelle. In addition, it is known that the volume change caused by binding of divalent metal ions to micelles is very small. The rate of rotation of the hydrated Na ion at the micellar surface is unlikely to change by more than 35% upon adsorption from the bulk to the Stem layer of SDS micelles.  

---

Figure 5.9 Dependence of the shape and structure of micelles on the molecular architecture of the basic surfactant units. The packing possibilities, based on simple geometrical features of the surfactants, build the final shape of the micelles.

---