DIRECT OBSERVATIONS OF TRANSITIONS BETWEEN CONDENSED LANGMUIR MONOLAYER PHASES BY POLARIZED FLUORESCENCE MICROSCOPY

Polarized fluorescence microscopy of Langmuir monolayers can distingui sh domains of different tilt azimuth in condensed phases of fatty acid s. The texture within a one-phase region is a mosaic of well-defined d omains that coarsen with time. Boundaries often contain sharp kinks, i mplying a significant anisotropy in the line tension between domains. The contrast between domains disappears at transitions between tilted and untilted phases. We report the first direct observation of the L2' '-CS transition and the swiveling transition (L2-L2'), which is marked by the instantaneous and reversible motion of isolated domain boundar ies. This transition leaves the domain morphology and the absolute til t direction largely unchanged, implying that molecules rearrange local ly to change the nearest-neighbor direction into the next nearest neig hbor. We also confirm the existence of a new phase transition observed by Overbeck et al.1 with Brewster angle microscopy.