Structural characterization of biphenyl ester-based LC molecules: Peculiarities of cyclic siloxane-based materials

The X-ray meridional profiles of a series of liquid crystalline molecules possessing the same mesogen but different siloxane-based backbones and spacer lengths are compared. Siloxane cores investigated include rings of different sizes, linear polysiloxanes, and short linear segments. The presence of diffuse, periodic reflections for ring-based compounds is attributed in part to translational association of the mesogenic units along the director (strings). The absence of these reflections in smaller, more flexible cores indicates that the localization of strong scattering units induced by the cyclic and linear cores also contributes to the strength of this molecular association. Correlations between measured correlation lengths, orientation parameters, and ''string'' lengths are discussed in detail. Preliminary molecular modeling is used to investigate the origins of these peculiar scattering phenomena as a function of the molecular architecture.