DOMAIN MORPHOLOGY IN A 2-DIMENSIONAL ANISOTROPIC MESOPHASE - CUSPS AND BOOJUM TEXTURES IN A LANGMUIR MONOLAYER

Brewster angle microscopy (BAM) and polarized fluorescence microscopy (PFM) were used to observe domains of a tilted condensed phase in coexistence with an isotropic liquid phase in Langmuir monolayers of pentadecanoic acid. The orientation of the molecular tilt direction inside the domains can be described as a ''virtual boojum'' texture and a cusp appears in the domain boundary at the vertex of the boojum. The angle subtended by the cusp increases with the domain size for domains greater than 25 mu m in diameter. All of these observations are at least qualitatively consistent with the recent predictions of a generalized Wulff construction for deformable materials [J. Rudnick and R. Bruinsma, Phys. Rev. Lett. (submitted)].