Journal of Physical Chemistry, Vol.98, No.31, 7430-7435, 1994
Observation of a Change from Splay to Bend Orientation at a Phase-Transition in a Langmuir Monolayer
The behavior of Langmuir monolayers of methyl octadecanoate, methyl nonadecanoate, and methyl eicosanoate has been 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 a splay to a bend texture), a process that we call "blooming". In other domains 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.
Keywords:AIR-WATER-INTERFACE;CHAIN FATTY-ACIDS;FLUORESCENCE MICROSCOPY;BREWSTER-ANGLE;FILMS;DIAGRAM;ORDER