Kinetics of Two-Dimensional Phase Transition of Langmuir Monolayers

Abstract

A theoretical model is introduced for the description of the two-dimensional condensation kinetics of Langmuir monolayers at the air/water interface. The dynamic jump of surface concentration of monomers and the dynamic jump of the surface pressure of compressible monolayers are theoretically described. For the dynamic jump of the surface pressure, the equation of state, introduced recently for Langmuir monolayers under equilibrium conditions, was used. The theoretical kinetic model accounts for different mechanisms of the monomer aggregation (dimerization, trimerisation, etc.) and different dependencies of the aggregation rate on t. The theoretical model is experimentally confirmed by the dynamic surface pressure−area curves of palmitoyl-d-allothreonin methylester monolayers recorded at different compression rates and temperatures. Good agreement between theory and experiment has been found with the consequence that the most preferred reaction at the aggregation is the attachment of molecules to large aggregates. The experimental results indicate that the rate constant depends quadratically on time. The activation enthalpies for the aggregation process in the palmitoyl-d-allothreonin methylester monolayers are calculated based on the dependence of the reduced rate constant k0 on temperature.