LAYERING AND CONFORMATIONAL TRANSITIONS IN THIN SURFACTANT FILMS

Amphiphilic molecules, such as the carboxylic acids and their salts, o rganic esters and alcohols, lipids, phospholipids and some other organ ic compounds have a tendency to form a wide variety of complex supramo lecular structures. These could be liquid crystalline layers, micelles , vesicles and different exotic multilayer patterns. Such properties a re essential for many biological processes and industrial applications . To describe these phenomena a theoretical model is proposed based on the weighted-density functional approach. Attention is focused on ord ering in surfactant films of amphiphilic compounds at the liquid-vapou r and liquid-liquid interfaces. These compounds contain one or several polar groups and a hydrophobic tail, which are responsible for the di fferent kinds of liquid-expanded-liquid-condensed and layering phase t ransitions in the films. Such transitions involve essential changes in the conformational or orientational states of the surfactant molecule s depending on their chemical composition and stiffness. Much experime ntal data for pi-A isotherms are consistent with the theoretical resul ts.