Temperature-induced transition to a nonmicellar state

We study the self-assembly of amphiphile molecules in water as a function of temperature and concentration in Monte Carlo simulations on a two-dimensional lattice, in which each water molecule occupies a single site, and each amphiphile occupies three sites. We determine the free amphiphile concentration and the aggregate-size distribution P(n) as functions of total surfactant concentration for different temperatures. The degree of micellar organization is characterized by Δ≡P(nmax)−P(nmin), where nmin and nmax>nmin are the aggregate sizes at which P exhibits its local minimum and maximum. We show that Δ vanishes continuously as we increase the temperature, and find the exponent associated with this micellar to nonmicellar transition.