Comparing molecular packing and textures of Langmuir monolayers of fatty acids and their methyl and ethyl esters

Langmuir monolayers of fatty acids and their methyl and ethyl esters show different textures. Stripe textures are observed in myristic acid monolayers. Continuous changes of molecular orientation occur in palmitic acid layers as well, although there are no stripe textures. In monolayers of fatty acid methyl and ethyl esters such continuous changes of orientation are not observed. The domains of methyl palmitate and ethyl palmitate are subdivided into segments of equal brightness. Grazing incidence synchrotron X-ray diffraction (GID) studies were performed to analyze the reason for this deviating behavior at the molecular level. The diffraction patterns of myristic acid suggest that the tilt azimuth is dispersed by about 5 degrees around a nearest-neighbor direction. Such dispersions of the tilt azimuth occur in palmitic acid and methyl palmitate layers as well. The monolayers of these substances differ from those of myristic acid only in the degree of the dispersion.