Small system thermodynamics is briefly discussed in relation to statistical mechanics and applied to solutions of noninteracting multi component micelles and vesicles. It is shown that the Gibbs-Duhem equation does not hold for the lipid membranes of vesicles as well as for micelles. Polydispersity of micelles and thermal fluctuations of the extensive thermodynamic functions are discussed, and equations of temperature and pressure dependencies of solubilities of surfactants in water are derived.
