The Isotropic-to-Nematic Transition in Semi-Flexible Micellar Solutions

We present a second virial theory of the isotropic-to-nematic phase transition in solutions of (polydisperse) wormlike micelles interacting via a hard-core excluded volume. Analytical expressions are derived for the osmotic pressures and the chemical potentials of the surfactant molecules in the coexisting phases. In systems where the mean micelle length is large compared to the persistence length P before the transition is reached, there is only a weak coupling between growth and orientational order. In contrast, when the micelles in the isotropic phase at coexistence are basically rigid ( ≪ P ), there is strong coupling; the properties of the nematic phase are then still controlled by flexibility effects.