Richard D. Smith

The collapse of surfactant monolayers at the air—water interface

Abstract The collapse pressures and collapse rates of nine different surfactant monolayers: oleic, myristic and stearic acid, methyl stearate, heptadecanol, octadecanol, nonadecanol, eicosanol, and dipalmitoyl lecithin (DPL), are determined experimentally using a Langmuir trough-Wilhelmy balance apparatus. All solid surfactants but DPL are found to collapse at rates consistent with a model of homogeneous nucleation and subsequent growth of bulk surfactant fragments. DPL films appear to collapse only by a fracture process. Oleic acid, the only liquid studied, collapses instantaneously at its equilibrium spreading pressure.