Dramatic enhancement of capillary wave fluctuations of a decorated water surface

Abstract

We have demonstrated by X-ray diffuse scattering that a bimolecular layer of a preformed three-tailed amphiphile, ferric stearate, drastically enhances capillary wave fluctuations on water surface due to a reduction in surface tension to 1 mN/m. The bimolecular layer is composed of molecules in symmetric configuration, on top of molecules in asymmetric configuration with ferric ions in contact with water. Unlike the usual Langmuir monolayers, this layer of molecules does not rupture under compression, but becomes thicker. This behavior mimics folding of a membrane on a liquid surface and is closely related to the cohesive interaction brought by the ferric ions. The low effective tension of this artificial membrane depends on the available area and reduces as the microscopic excess area increases.