The Raman Spectra of Aligned Thin Films of Nematic Liquid Crystals

Abstract

Abstract The Raman spectra of thin films of nematic liquid crystals, MBBA and NP-5A, have been measured for samples sandwiched between two glass (or quartz) plates, which had been pretreated in several ways. The intensities of the fundamental bands of the molecules and the polarization components of each band depend on the molecular orientation structures, such as the homogeneous and homeotropic alignments. The intensity ratio provides a semi-quantitative measure for the molecular orientation, and the Raman results are compared with those from polarizing microscopic observations and infrared spectra. The molecular orientation of the liquid crystals varies with the concentrations of surface-active agents as well as the materials used for the pretreatment of the plates. The molecular interactions, which give rise to the orientation structures, are briefly discussed.