Browsing by Author "Nian, Yu-Lin"

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Conditions for the formation of a uniformly lying helix structure induced by the electrohydrodynamic effect
(2017-01-01)
Nian, Yu-Lin
;
Wu, Po-Cheng
;
Lee, Wei
;
影像與生醫光電研究所
;
Institute of Imaging and Biomedical Photonics
The uniform lying helix (ULH) structure in a cholesteric liquid crystal (CLC) cell has been widely discussed in the literature. Based on the electrohydrodynamic (EHD) effect, we have suggested that the voltage-induction of a well-aligned ULH state can be fine-tuned in a CLC cell by optimizing both the amplitude and the frequency of the applied voltage. However, since the EHD effect is correlated with the migration of mobile ions within the bulk of the cell, the ionic conditions for such an EHD-induced ULH state have not been clarified. In this research, we focus on studying the influence of ion density and the diffusivity on the formation of the EHD-induced ULH structure in a CLC cell, followed by finding out some key conditions for the generation of well-aligned ULH states.
Optimized frequency regime for the electrohydrodynamic induction of a uniformly lying helix structure
(2016-12-01)
Nian, Yu-Lin
;
Wu, Po-Chang
;
Lee, Wei
;
光電學院
;
College of Photonics
This study specifies the optimal frequency regime for the uniformly lying helix (ULH) alignment induced by the electrohydrodynamic (EHD) effect in a cholesteric liquid crystal with positive dielectric anisotropy. Based on the transport behavior of ionic charges in response to the externally applied ac electric field, four frequency regimes, divided by three critical frequencies (i.e., f (L), f (R), and f (H)), are identified by means of dielectric spectroscopy. By discussing the voltage-dependent cholesteric textural changes in each frequency regime in terms of the voltageand frequency-dependent transmission spectra and optical textures, our results suggest that the designated frequency regime f (L), < f < f (R), where electrical charges can effectively oscillate in the bulk of the cell with less ion accumulation on the electrode surfaces, is most adequate for the generation of well-structured ULH via effective induction of the EHD flow by the external voltage. As a result, this study provides a pathway to determination of the optimal frequency regime for generating the EHD-induced ULH state prior to voltage treatment. (C) 2016 Chinese Laser Press