Self-consistent-field prediction for the persistence length of wormlike micelles of nonionic surfactants

The persistence length of wormlike micelles is predicted using a molecular realistic self-consistent-field theory by analyzing the curvature energy stored in toroidal micelles. It is assumed that the growth of the torus is unidimensional and its cross section is a perfect circle with radius of the torus Rt and curvature J = 1/Rt. For CnEm nonionic surfactants, it is found that the persistence length lp scales with respect to the tail group length n as lp ~ nx where x is about 2.4-2.9. For sufficiently long hydrophobic tail length, the wormlike micelles become more rigid with increasing temperature and for short-tail surfactants, the reverse is found. Remarkably, curvatures in the order of the inverse persistence length are such that J4 and J6 terms are needed to know the bending energy for this case. This effect is more pronounced the larger the head and the smaller the tail group