Infrared and Raman Spectroscopy of Liquid Crystals

Abstract

Liquid crystals are complex organic systems exhibiting a variety of interesting phase transitions. In this paper, work is reviewed in two areas: (1) lattice dynamics of nematogenic crystals as the crystal-nematic liquid crystal phase transition is approached, and (2) vibrational spectroscopic changes at the gel-liquid crystal phase transition of phospholipid-water mixtures. In each area, a case is made that interpretable spectroscopic information can be obtained from a system of this complexity. For the lattice vibrations, a model potential is used to calculate vibrational frequencies. These in turn are discussed in terms of motions which might be uncoupled as the crystal-nematic transition is approached. For the lipid vibrations, infrared and Raman data show how chain melting manifests itself in the spectrum. An application of this to phase diagram construction is presented.