FT-IR TRS of Liquid Crystalline 5CB in ac,dc,and ac + dc Electric Fields

Abstract

Time-resolved (TR) spectra of 5CB in the millisecond domain were obtained during excitation with electric fields of different time dependence: ac, dc, and ac + dc. The response to ac excitation occurs mainly at twice the modulating frequency. The effect of the addition of dc to an ac field is the induction of an additional response at the ac frequency. The additional “single frequency” response persists indefinitely, even though the response to the application of only a permanent dc field relaxes within roughly 200 ms. The amplitude of the oscillating responses diminishes with increasing ac frequency. This result is in accordance with the expected response to the torque exerted by the ac field. Different functional group absorptions respond without a significant phase difference in this time scale.