Double modulation FTIR spectroscopy of ferroelectric liquid crystals under electric field

Molecular reorientation of ferroelectric liquid crystals, under alternating electric field, is investigated using a double modulation FTIR spectroscopy. This method combines the high frequency modulation of the applied electric field with the light modulation produced by the interferometer at lower frequency. Originally the liquid crystal is oriented between two conducting infrared transparent windows. Simultaneous acquisition on two channels of the high frequency and low frequency interferograms allows to get a signal DELTAA that is only dependent on the molecular group reorientation induced by the applied field. The experimental setup and quantitative aspects of the obtained signal DELTAA are described. Some results are presented in order to show the effect of the temperature, applied electric field and its frequency on the reorientation properties of the studied liquid crystal.