Kinetics of phase transitions in monolayers: collapse

Abstract

Although monolayers at the air/water interface have been the subject of intense study over the past 15 years, they continue to be actively investigated as evidenced by the topics discussed in this workshop. Such films continue to be employed for investigations of subjects as diverse as chain packing, critical phenomena, two-dimensional flow and wetting, biological catalysis, membrane physics and the kinetics of phase transitions. We examine the kinetics of monolayer collapse, the transition between two and three dimensions, for 2-hydroxytetracosanoic acid. The studies include measurements of surface pressure-area isotherms and imaging in situ by light-scattering microscopy. Three mechanisms of collapse have been observed: (equation 1) slow collapse by the nucleation and growth of multilayer islands; (equation 2) the formation of giant folds into the subphase; and (3) long multiple folds of small amplitude. Both folding modes are reversible. The slow collapse occurs at low surface pressures and the folding at high pressures, with the giant folds appearing only at low compression rates.