Surface Effects on Anchoring and Dynamical Interactions of Liquid Crystalline Films

Abstract

Effects of surface morphology and chemistry are studied on nanoscale liquid crystalline (LC) films of 4-n-pentyl-4' -cyanobiphenyl (5CB) via polarized Fourier-transform infrared (FTIR) and step-scan time-resolved vibrational (TRS) spectroscopies. Surface-induced alignments and electro-optical dynamics of these systems are examined in a systematic manner, in a cell whose geometry enables thorough investigation of orientational transitions. In the experiments detailed in this work, anchoring imparted by nanoscale textures are examined, in which it is discovered that spicular corrugation on the surface induces a homeotropic alignment, whereas a grooved morphology promotes a planar and homogeneous alignment. In a cell whose surfaces are modified chemically by amorphous polyimide layer, the initial anchoring induced is planar, with the azimuthal orientation governed by flow and shear. Temperature effects on the stability of nematic fluid structure and dynamics are also probed in an LC system whose surface effects are well characterized. The results from these experiments suggest that the initial anchoring imparted by the surface determines the mechanism via which the 5CB films reorient under the application of external field. The dynamics of these transitions are, as a result, mediated by the elastic intermolecular interactions of the induced mode of deformation. A simple theory-based model, which provides insight into the anchoring and dynamical interactions of these nematic LC systems, is presented.