Browsing by Author "Shih, WT"

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Field-induced reorientation dynamics of a surface stabilized ferroelectric liquid crystal mixture
(2004-03-01)
Shih, WT
;
Huang, JY
;
Zhang, JY
;
光電工程學系
;
Department of Photonics
Time-resolved measurements of electro-optical response and Fourier-transform infrared absorption have been employed to study the submolecular motion of a surface stabilized ferroelectric liquid crystal (SSFLC) mixture during a field-induced reorientation process. All observed submolecular groups were found to rotate in unison about the layer normal in a steady d.c. field. In a transient situation, the FLC director can respond rapidly to a pulsed driving field. However, the orientation distribution was found to spread at first and then slowly converge to the new direction of the FLC director. When the field is switched off, all the core groups relax to a steady-state direction with varying relaxation times. The results reveal that submolecular fragments of different molecular species in the FLC mixture move correlatively in a steady d.c. field and during a field-induced reorientation process.
Molecular alignment and field-induced reorientation in a twisted nematic liquid crystal pi-cell
(2002-10-01)
Shih, WT
;
Huang, JY
;
光電工程學系
;
Department of Photonics
A twisted nematic pi-cell has been studied by optical transmission measurement, polarized Fourier-transform infrared (pFTIR) absorption spectroscopy, and Raman spectroscopy. Our pFTIR results suggest that the LC molecules undergo a restricted rotation about the molecular long axis. The rise and decay times of the optical response were found to be 6 ms and 1.6 ms, respectively. The switching dynamics of the twisted pi-cell was also studied using time-resolved Raman spectroscopy. A normal mode associated with the C-H out-of-plane wag on the LC core was found to be enhanced after the electric field was switched off. Our data show that LC molecules in the twisted pi-cell do not rotate like a rigid molecule during the field-induced reorientation process. The methods employed in this study have yielded valuable information about LC alignment and field-induced reorientation with respect to functional group specificity.