Correlations in interfaces with surfactants

The existence or nonexistence of the bending coefficient in liquid interfac es: as well as the applicability of the Helfrich Free energy, is examined b y comparing correlations in the interfaces with or without a weak surfactan t. In the latter case, the formation of a bilayer is studied and density-de nsity correlations and height-height correlations are reported, analyzed, a nd compared with "normal" liquid interfaces. In particular, the role of lat eral tension is discussed.