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° (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. © 1994 American Chemical Society.

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