Anisotropy in Langmuir Layers of a Bent-Core Liquid Crystal

Langmuir layers of a symmetric bent-core molecule with hydrocarbon end chains and two chlorine atoms substituted on the central phenyl ring of the bent core were characterized by a combination of surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. These layers were found to be optically anisotropic, in contrast to Langmuir layers of similar molecules with different substitutions on the core. After compression, the orientation of the optical axis was essentially uniform over the film. Upon decompression, the film broke into uniform islands or domains. Measuring domain reflectivity while changing the domain orientation allowed the determination of thetilt angle with respect to both domain features and the film normal, as well as the refractive index anisotropy. The tilt angle, near 90°, suggests that the bent-core molecules lie quite flat on the surface.