Theoretical Description of Mixed Film Formation at the Air/Water Interface: Carboxylic Acids-fatty Amines

Clusterization thermodynamic parameters of mixed monolayers of aliphatic amines CnH2n+1NH2 and carboxylic acids CnH2n+1СОOH (n=6-16) are calculated using the quantum chemical semi-empirical PM3 method. Four types of mixed dimers and tetramers amine-acid are considered. The total contribution of interactions between the hydrophilic parts of amine and acid into clusterization Gibbs’ energy is slightly lower than the corresponding interactions for individual surfactants. It suggests synergetic interaction between the regarded amphiphilic compounds proved by experimental data in literature. Two types of competitive film formation are possible: mixed 2D film 1, where the molecules of the minor component are single distributed among the molecules of the prevailing second component (mixture of components on molecular level) and 2D film 2 of domain structure comprised of separate regions of the same components bound together. The dependence of the clusterization Gibbs’ energy per monomer of 2D film 1 on the compo...