The blooming transition in Langmuir monolayers and its microscopic origin

The behavior of Langmuir monolayers of methyl octadecanoate, methyl nonadecanoate and methyl eicosanoate was studied by polarized fluorescence microscopy and Brewster angle microscopy in the neighborhood of a transition between two liquid-condensed (LC) phases. As the monolayer is cooled through the transition, the molecular tilt azimuth in six-arm star defects of the LC phase changes by 90 degrees (from play to bend texture), a process called ''blooming''. In other defects, the transition is seen as a change from textured distorted hexagons to rectangular domains in which the tilt direction is uniform, The changes in texture and morphology are consistent with a transition from a hexatic phase to a crystalline phase with herringbone order.