Ternary surfactant mixtures in semi-infinite geometry

Oil-water-surfactant mixture is investigated near the planar surface by mea n-field theory applied to a certain lattice model. Close to the coexistence of the microemulsion with the lamellar phase, the model predicts either su rface-induced ordering or surface-induced disordering transitions, dependin g on the nature of the surface. The new order-parameter, describing the lam ellar order, is defined. The Landau-Ginzburg functional based on the new "l amellar order parameter'' is introduced. The functional has a form introduc ed earlier for surface-induced ordering and disordering in simple fluids. C onnection of the continuous model to the lattice one is discussed. (C) 1999 American Institute of Physics. [S0021-9606(99)51115-X].