THE BLOOMING TRANSITION IN LANGMUIR MONOLAYERS AND ITS MICROSCOPIC ORIGIN

The behavior of Langmuir monolayers of methyl octadecanoate, methyl no nadecanoate and methyl eicosanoate was studied by polarized fluorescen ce microscopy and Brewster angle microscopy in the neighborhood of a t ransition between two liquid-condensed (LC) phases. As the monolayer i s 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 transi tion is seen as a change from textured distorted hexagons to rectangul ar domains in which the tilt direction is uniform, The changes in text ure and morphology are consistent with a transition from a hexatic pha se to a crystalline phase with herringbone order.