Browsing by Author "Chen, Hsin-Li"

Now showing 1 - 3 of 3

Dielectric characterization and voltage holding ratio of blue-phase cells
(2016-09)
Wu, Po-Chang
;
Hsu, Hsuan-Tsung
;
Chen, Hsin-Li
;
Lee, Wei
;
光電學院
The phase behaviors of a blue-phase (BP) liquid crystal in a planar-aligned cell were investigated by means of temperature-dependent dielectric spectroscopy. With auxiliary observations of optical transmission spectra and birefringent textures, we found that the transition temperatures of two adjacent mesophases, including the cholesteric-to-BPI, the BPI-to-BPII, and the BPII-to-isotropic, can clearly be distinguished by the first and second derivatives of the real-part dielectric permittivity function to the temperature at a specific frequency. Furthermore, an attempt to evaluate the device performance of a polymer-stabilized BP, derived from the photopolymerization of two monomers (R1V1257 and TMPTA), was achieved with a new circuital design for the voltage-holding-ratio (VHR) measurement. Preliminary results of the VHRs of samples at 180 Hz and their temperature dependence were obtained accordingly. (C) 2015 Elsevier B.V. All rights reserved.
Dielectric characterization and voltage holding ratio of blue-phase cells
(2016-09-01)
Wu, Po-Chang
;
Hsu, Hsuan-Tsung
;
Chen, Hsin-Li
;
Lee, Wei
;
光電學院
The phase behaviors of a blue-phase (BP) liquid crystal in a planar-aligned cell were investigated by means of temperature-dependent dielectric spectroscopy. With auxiliary observations of optical transmission spectra and birefringent textures, we found that the transition temperatures of two adjacent mesophases, including the cholesteric-to-BPI, the BPI-to-BPII, and the BPII-to-isotropic, can clearly be distinguished by the first and second derivatives of the real-part dielectric permittivity function to the temperature at a specific frequency. Furthermore, an attempt to evaluate the device performance of a polymer-stabilized BP, derived from the photopolymerization of two monomers (R1V1257 and TMPTA), was achieved with a new circuital design for the voltage-holding-ratio (VHR) measurement. Preliminary results of the VHRs of samples at 180 Hz and their temperature dependence were obtained accordingly. (C) 2015 Elsevier B.V. All rights reserved.
Electro-optical and dielectric properties of polymer-stabilized blue phase liquid crystal impregnated with a fluorine-containing compound
(2018-10-01)
Wu, Po-Chang
;
Chen, Hsin-Li
;
Rudakova, Natalya V.
;
Timofeev, Ivan V.
;
Zyryanov, Victor Ya.
The effects of a fluorine-containing compound (4,4'-difluorobenzophenone; DF) on the electro-optical and dielectric properties of polymer-stabilized blue phase (PSBP) liquid crystals were investigated. When a PSBP cell was driven by an in-plane electric field, the addition of DF up to 2.7 wt% effectively reduced the operation voltage by-30%. Further inspection by dielectric spectroscopy indicated that the ionic concentration in PSBP decreased with increasing loading of OF. This finding can be ascribed to the complexation of impurity ions near the ketone group and carbon-fluorine bonds of the DF compound that restrained the ion transport after photopolymerization. As a result, the DF compound can be regarded as a superior ion-suppressor, enabling the reduction in the ionic effect and, in turn, the promotion of the electro-optical response of a PSBP. (C) 2017 The Authors. Published by Elsevier Inc.