Effect of chiral interactions on the structure of Langmuir monolayers

Structural changes in monolayers of the enantiomer and the racemic mixture of 1-hexadecyl-glycerol with temperature and surface pressure variations are compared. On compression, both monolayers exhibit a variation of the tilt azimuth from the direction to the nearest neighbor to the next nearest neighbor. In the monolayer of the racemate, this variation occurs as a first order transition. In the monolayer of the enantiomer, the unit cell is oblique, and continuously passes from a state close to the low-pressure state of the racemate to a state close to its high-pressure state. The azimuths of the unit-cell distortion and that of the tilt remain almost equal to each other. The effect of chirality decreases when the temperature is increased. Structural changes are explained in detail within the framework of the Landau theory of phase transitions.