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 coex istence with an isotropic liquid phase in Langmuir monolayers of penta decanoic acid. The orientation of the molecular tilt direction inside the domains can be described as a ''virtual boojum'' texture and a cus p appears in the domain boundary at the vertex of the boojum. The angl e subtended by the cusp increases with the domain size for domains gre ater 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. Bruinsm a, Phys. Rev. Lett. (submitted)].