PHD, Kent State University, 2007, College of Arts and Sciences / Department of Physics

A Langmuir film is a molecularly thin layer self confined at a liquid/vapor interface (typically air/water). We studied Langmuir layer of bent-core molecules which have bent cores with phenyl rings and two long and flexible end-chains. Due to their special molecular structure, bent-core molecules exhibit a rich variety of phases, including many liquid crystalline ones. A dozen different liquid phases and five smectic phases have been suggested. At least eight phases have been identified, but most have not been fully characterized. The usefulness of bent-core molecules in all kinds of devices has been demonstrated. Studies of growth mechanism, molecular ordering, and the overall film morphology are of prime importance for device design. The Langmuir layer can give insight into the molecular packing within layers, particularly in the presence of an interface. For bulk liquid crystal, the order at this interface can help in understand the order in bulk. Bent-core molecules that show smectic ordering, even if only at higher temperatures, may be expected to form reversible collapsed layers. A stable Langmuir layer, transferred to a solid interface, may form a natural alignment layer for bent-core liquid crystals. It has been very difficult to align bent-core molecules, and many of the zero-field characteristics have had to be deduced from quite inhomogeneous films. Studies of Langmuir layers may thus help clear up structural questions about bent-core liquid crystals in two ways: directly, by what can be deduced from the structure of the Langmuir layers themselves, and indirectly, through the possibility of providing a suitable alignment layer to produce more homogeneous, thicker films. My work concentrated on two kinds of bent-core molecules: One with siloxane end-chains and the other with hydrocarbon end-chains. Both the bent-cores and end-chains will be varied. Systematic study will be carried on some particular molecule. The experimental methods includes: Surface Pres (open full item for complete abstract)

Committee: Elizabeth Mann (Advisor) Subjects: