Thermodesorption processes of langmuir layers of aliphatic acids and salts

Thermodesorption processes of mono-and multilayers of fatty acids and their salts with 14 to 24 carbon atoms were investigated by ellipsometry and IR spectroscopy. Cadmium, calcium, strontium, and barium salt layers, unlike the layers of pure acids, have a complex phase composition which includes not only separate acid and salt phases, but also intermediate acid-salt forms. The initial phase composition of multilayer systems determines their thermodesorption spectrum observed upon heating the samples. It was found that before the removal of molecules to the gaseous phase, phase transitions are possible in the films, similar to those observed in crystals and caused by the change of molecular conformations in the layer. Energy characteristics of thermodesorption processes are estimated for pure acid layers and for separate phases in salt layers. Possible qualitative models of the processes are discussed.