NEMATIC STABILITY AND THE ALIGNMENT-INDUCED GROWTH OF ANISOTROPIC MICELLES.

We treat for the first time a phenomenon in micellized soap solutions which arises uniquely from their being colloidal suspensions whose 'particles' do not maintain their integrity. We consider a simple analytical form for the free energy per molecule and compare explicitly the sizes of rod-like micelles in coexisting isotropic (I) and nematic (N) phases. Within Onsager's theory for the long-range alignment of rod-like particles, we conclude that: (i) the growth of micelles at the I yields N transition is driven largely by the orientatial 'entropy of mixing' - bigger rods allow this entropy loss to be minimized; and (ii) the nematic order parameter and the ratio of coexisting sizes are essentially universal, with the average volume fraction at the transition scaling as the reciprocal of the average aggregation number.