Two-Dimensional Infrared Spectroscopy of Electric-Field-Induced Reorientation Dynamics of a Mixed Nematic Liquid Crystal

Abstract

A two-dimensional infrared (2D IR) spectrometer has been modified by the following methods to solve several problems on the 2D IR spectroscopy of electric-field-induced reorientation dynamics of a mixed nematic liquid crystal: (1) The response of the liquid crystal (LC) to an electric field was stabilized by an amplitude-modulated ac electric field. (2) Formulation of an anti-reflection coating (ARC) has been proposed to suppress the interference caused by multiple reflections between IR liquid crystal cell windows. (3) The Fourier transform procedure has been modified to correct the phase of the dynamic difference interferograms without spectral anomalies. These modifications can provide a better signal-to-noise ratio and reproducible 2D IR spectrum of a mixed nematic liquid crystal.

Reorientation of Nematic Liquid-Crystals and Liquid-Crystalline Polymers in an Electric Field Studied by FT-IR Time-Resolved Spectroscopy and 2D-Correlation Analysis

“…A combination of FT-IR time-resolved spectroscopy with 2D-correlation analysis is the most powerful tool to study time-dependent spectral intensity changes induced by an external perturbation and can provide many details on the movement of particular molecular segments. Since the first application of the 2D-correlation analysis to time-resolved spectra of a liquid crystal (5CB), numerous similar studies from different laboratories have been reported. ,, However, to our best knowledge, this is the first example of using the general 2D formalism 24 to investigate the electric-field-induced reorientation of LCs.…”

“…Since the first application of the 2D-correlation analysis to time-resolved spectra of a liquid crystal (5CB), 8 numerous similar studies from different laboratories have been reported. 11,25,26 However, to our best knowledge, this is the first example of using the general 2D formalism 24 to investigate the electric-field-induced reorientation of LCs.…”

FOURIER TRANSFORM INFRARED VIBRATIONAL SPECTROSCOPIC IMAGING: Integrating Microscopy and Molecular Recognition

“…In particular, TR-FTIR spectroscopy involving stable step-scan (16) interferometry (61,62) has been utilized to monitor dynamic phenomena in wide-ranging systems, including the dynamics of biological molecules, reaction and binding mechanisms, rheo-optics of polymeric materials, and laser emissions. The reorientation dynamics of liquid crystalline materials responding to externally applied electric fields also is an area of considerable activity (63)(64)(65)(66)(67)(68).…”

Time-Resolved Fourier Transform Infrared Spectroscopic Imaging

“…The reorientation dynamics of liquid crystalline materials responding to externally applied electric elds also represents an area of considerable activity. [16][17][18][19][20][21] In these studies, an external electrical eld applied to nematic liquid crystals (LC) reorients the molecular director in a manner determined by the direction and strength of the eld; rem oval of the perturbation allows the ensemble's average director to assume its original orientation. Events in the reorientation and subsequent relaxation processes occur on time scales ranging, for example, from picoseconds for intra-molecular changes to milliseconds for the rotation of an entire LC m olecule.…”