Application of Infrared ATR Spectroscopy to Liquid Crystals. I. Surface-Induced Orientation in Thin Films of Nematic MBBA

Abstract

Abstract Infrared dichroism of nematic liquid N-(p-methoxybenzylidene)-p-butylaniline (MBBA) was measured using a conventional transmission method and an ATR method. In the former, KBr windows were used as substrates. The degree of orientation order of the homogeneous structure, which was achieved by a rubbing procedure, was obtained to be S=0.40. Using the measured dichroic ratios, the angles between the transition moments and the long axis of the molecule were calculated. The calculated values are in satisfactory agreement with the molecular conformation already suggested. In the ATR method, In2O3-coated glass plates were used as substrates. Rubbing of the In2O3 surface gave a uniform homogeneous orientation with an S value of 0.57. An In2O3 surface treated with dimethyldichlorosilane gave a homeotropic texture with an S value of 0.53. The directions of the transition moments relative to the long axis of the molecule closely agreed with those obtained from transmission spectra.