Using a Ginzburg-Landau free energy, we show that the failure of an oil/water interface to be wetted by a microemulsion is directly related to its structure. At the disorder line where the fluid loses this structure, an unusual wetting transition can occur. We calculate the elastic constant of mean curvature for both oil/water and oil/microemulsion interfaces. Employing a lattice model, we show that an incipient lamellar phase instability leads to ultralow interfacial tensions between oil and water when coexisting with a microemulsion.

• Received 12 March 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.1116