Molecular theory of rod-shaped micelles.

Rod formation is primarily governed by the characteristic Gibbs free energy of rod formation, ΔGrod. Geometrically, a rod-shaped micelle consists of a central cylindrical part of hydrocarbon radius rc and of more or less hemispherical parts at the ends of hydrocarbon radius rs. To smooth out the transition region between the spherical part of an endcap and the cylindrical part a catenoid is introduced. The model includes hydrophobic, electrostatic, and steric interactions, and allows direct adsorption of counterions to the micelle surface. It is used to calculate the optimal radius of the cylindrical part and to determine the according equilibrium configuration of the endcaps. The theoretical results are compared with empirical data for cetylpyridinium salts. Direct counterion adsorption is found to amount to about 50%. A strong steric influence on counterion adsorption is given. [ABSTRACT FROM AUTHOR]