Collapse of a Monolayer by Three Mechanisms

The collapse of monolayers of 2-hydroxytetracosanoic acid at the air/water interface has been examined by measurements of surface pressure−area isotherms and imaging with light scattering microscopy. Topographic images of films transferred to mica by the Langmuir−Blodgett technique have also been obtained. At low pressures, the films undergo “slow collapse” by the formation of multilayer islands. Folding occurs at high-pressure plateaus. At low compression rates, “giant folds” into the subphase arise at defects. They are composed of bilayers that remain suspended beneath the film and open reversibly during expansion. At higher rates of compression, the dominant collapse mechanism is by the formation of small-amplitude “multiple folds” that extend across the trough and are perpendicular to the compression direction.