Formation of highly condensed ferric stearate monolayers at the air-water interface

Pressure-molecular area isotherms of a Langmuir monolayer of preformed ferric stearate on water have been studied at various temperatures, compression rates, and pH values. The isotherms indicate anomalously small areas per molecule for the ferric stearate monolayers. A probable model is put forward to explain the small molecular areas. This model retains the area per hydrocarbon chain to 18 Angstrom observed in other similar systems, with a head-to-tail ratio of 1:3, but assigns a dominant role to hydrophobic forces in forming and stabilizing the monolayer. The X-ray reflectivity profile calculated from this model matches well with the measured data of deposited Langmuir-Blodgett film of ferric stearate.