STEP-SCAN FT-IR TIME-RESOLVED SPECTROSCOPY (S-2(FT-IR)-TRS) OF THE ELECTRO-REORIENTATION OF LIQUID-CRYSTALLINE MATERIALS

Frequency domain and time domain step-scan FT-IR rime-resolved spectra (S2FTIR TRS) of the homogeneous/homeotropic transition in several nem atic liquid crystals are presented and discussed. These include the pu re mesophases 5CB and 5PCH and the eutectic mesophase 7A. In agreement with previous studies, both frequency domain and time domain data ind icate a difference in response of the rigid and ''floppy'' segments of the 5CB and 5PCH molecules. The time domain data show clearly that it is in the recovery (voltage off) phase that the pentyl ''tails'' of t he molecules respond more quickly than the rigid cores. For 7A, freque ncy domain data collected at twice the AC field frequency and with zer o DC offset, indicate a slight difference in phase of response of the two major components.