Application to Liquid-Crystal Orientation Dynamics

One published application of time-resolved asynchronous FT-IR spectrometry involves the reorientation dynamics of ferroelectric liquid crystals induced by the reversal of the external electric field [26,27]. For the study to be described here, the liquid crystals were held in a 2-pm CaFa cell whose windows had been coated with indium tin oxide, which served as the electrode, and with a polyimide film that had been oriented by stroking it in one direction. After the sample had been heated to 90° C to ensure that it was all in the isotropic liquid phase, it was injected into the cell, which had been heated to the same temperature. The cell was then allowed to cool to 40°C at a rate of 1°C min to obtain a homogeneously oriented liquid crystal. An IR polarizer was set at an angle of 45° to the orientation direction of the liquid crystal to obtain the maximum change in the absorption spectrum. Rectangular electric pulses with 20-V peak voltages and a 20-ps period were applied to the cell. 

Similar experiments have also been carried out with a step-scan FT-IR spectrometer [28], and analogous results were obtained. Although this experiment was not performed with very short time resolution, it gives an idea of the quality of the data that can be obtained, and successful experiments with much shorter time resolution can be predicted. 

R Hinsmann, M. Haberkorn, J. Frank, P. Svasek, M. Harasek, and B. Lendl, AppL Spectrosc. 55, 241 (2001). 

Vogel and F. Siebert, Curr. Opin. Chem. Biol. 4, 518 (2000). 

Katayama, T. Sato, Y. Ozaki, K. Murashiro, M. Kikuchi, S. Saaito, D. Demus, T. Yuzawa, and H. Hamagucbi, Appl. Spectrosc. 49, 977 (1995). 

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