Langmuir films of liquid crystalline materials: The influence of molecular architecture on morphology and properties

The differences in the Langmuir film properties of a liquid crystalline homopolymer, its corresponding mesogenic side group moiety, and two copolymers are discussed. The results from Brewster angle microscopy are compared with those from the standard methods that are commonly used to infer the structure of a monolayer (i.e., isotherms). As expected, the viscosity and stability of the films increased for the homopolymer while the onset mean molecular area (MmA) remained similar to that of the monomer. Although this similarity may lead to the assumption that the structure of the two films is the same, Brewster angle microscopy showed a distinct difference between both compounds. Whereas the monomer exhibits liquid crystalline condensed phases with large domains in which the molecular tilt is uniform, the homopolymer is in a solid amorphous state without any uniformly tilted regions large enough to be observed by the microscope. In contrast to the homopolymer, the copolymer is highly fluid with a distinctly higher MmA. Again, no domains with a uniform tilt were observed, probably due to the increased distance between the mesogens. © 1993 American Chemical Society