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 no nadecanoate, and methyl eicosanoate has been studied by polarized fluo rescence microscopy and Brewster angle microscopy in the neighborhood of a transition between two liquid-condensed (LC) phases. As the monol ayer is cooled through the transition, the molecular tilt azimuth in s ix-arm star defects of the LC phase changes by 90 degrees (from a spla y to a bend texture), a process that we call ''blooming''. In other do mains the transition is seen as a change from textured distorted hexag ons to rectangular domains in which the tilt direction is uniform. The changes in texture and morphology are consistent with a transition fr om a hexatic phase to a crystalline phase with herringbone order.