PHASE-TRANSITION FROM A LIQUID EXPANDED TO A LIQUID CONDENSED SURFACTANT MONOLAYER

Citation
E. Ruckenstein et Bq. Li, PHASE-TRANSITION FROM A LIQUID EXPANDED TO A LIQUID CONDENSED SURFACTANT MONOLAYER, Journal of physical chemistry, 100(8), 1996, pp. 3108-3114
Citations number
33
Categorie Soggetti
Chemistry Physical
ISSN journal
00223654
Volume
100
Issue
8
Year of publication
1996
Pages
3108 - 3114
Database
ISI
SICI code
0022-3654(1996)100:8<3108:PFALET>2.0.ZU;2-8
Abstract
Liquid monolayers of insoluble surfactants at the air/water interface are treated as a two-dimensional solution made up of molecules with di sordered chains and clusters of molecules with ordered chains. The Flo ry-Huggins equation is used to calculate the activities of the species . On this basis, the phase transition from the Liquid expanded to the liquid condensed state is predicted. Depending on the value of the int eraction parameter between disordered and ordered molecules and the ex tent of clustering, the theoretical pi-A isotherms exhibit either a fi rst-order phase transition or a nonhorizontal, second-order, phase tra nsition. For the tetradecanoic, pentadecanoic, hexadecanoic, and hepta decanoic fatty acids, the theoretical pi-A isotherms are in agreement with experimental data. It should be emphasized that the theory is pre dictive since all the parameters are calculated on the basis of the mo lecular structure.