MOLECULAR-ORGANIZATION OF A PYRAMIDIC LIQUID-CRYSTAL AT THE AIR-WATER-INTERFACE

Films of the pyramidic liquid crystals hexakis(nonanoyloxy)tribenzocyc lononene and hexakis(pentadecanoyloxy)tribenzocyclononene spread at th e air-water interface have been studied using grazing incidence X-ray reflectrometry. Both compounds exhibit a transition from an expanded p hase to a condensed phase. In the expanded phases as well as in the co ndensed phase of hexakis(pentadecanoyloxy)tribenzocyclononene the mole cules lie flat on the surface. The density and the thickness measured in the condensed phase of hexakis(nonanoyloxy)tribenzocyclononene are only consistent with an ''edge-on'' configuration. This latter phase i s metastable with respect to the growth of three-dimensional domains w hose thickness, orientation, and lattice parameters are determined and compared to bulk lattice parameters.