Surface phenomena for lamellar phases in microemulsions

Surface phenomena in fluids exhibiting structure on the nanoscale (microemu lsions, copolymers etc.) are studied. We argue that far such systems the La ndau-Ginzburg functional of suitably chosen order parameter should on the n anoscale have the same form, as the Landau-Ginzburg density-functional for simple fluids on the microscale. We define such order parameter for lamella r ordering by averaging the lamellar structure given by density profiles ov er a period of the density oscillations. The resulting Landau-Ginzburg func tional leads to surface-induced order or disorder and to the associated wet ting phenomena. We verify our hypothesis by explicit mean-field calculation s in a lattice model of microemulsions in the presence of a surface. Perfec t agreement is found. Our results also agree with recent experiments.