Orientation and Dynamics of Nanoscale Liquid Crystalline Films

Abstract

The behavior of nanoconfined liquid crystalline thin films on the order of 40 to 300 nm in thickness has been investigated. An infrared-transparent cell of unique design was constructed using microfabrication techniques. The cell is comprised of ZnSe substrates and a gold interdigitated array electrode; it is designed to confine the liquid crystals into nanocavities and allow spectroscopic measurement of the confined films by transmission Fourier-transform infrared spectroscopy (FTIR). The homogeneity of the surface-induced orientation is largely dependent on the thickness of the films. A 40 nm film demonstrates surface anchoring in the strong binding limit, while a thicker 300 nm film, though still showing strong surface effects, exhibits more bulk-like properties. The surface-induced orientation is largely dependent on the morphology of the substrate. Corrugations in the ZnSe promote homeotropic (surface normal) alignment of the liquid crystals while grooves initiate a planar alignment. Both film thickness and substrate morphology have a profound effect on the rate of the electric-field induced orientation and subsequent relaxation of the confined films. It has also been shown that the ZnSe surface can be chemically modified (and patterned via microcontact printing (muCP)) by the adsorption of Self Assembled Monolayers (SAMs) of thiols and functionalized thiols. This is of particular interest for future studies of molecularly tailored surfaces for directing the orientation of liquid crystalline thin films.