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Crystals 2017, 7(7), 227;

Electrohydrodynamics-Induced Abnormal Electro-Optic Characteristics in a Polymer-Dispersed Liquid Crystal Film

Department of Photonics and Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan 701, Taiwan
Department of Electro-Optical Engineering, Kun Shan University of Technology, Tainan 710, Taiwan
Department of Optometry, Chung Shan Medical University, Taichung 402, Taiwan
Department of Ophthalmology, Chung Shan Medical University Hospital, Taichung 402, Taiwan
Department of Physics, Tunghai University, Taichung 407, Taiwan
Graduate Institute of Electrical Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 824, Taiwan
Authors to whom correspondence should be addressed.
Academic Editor: Wei Lee
Received: 14 June 2017 / Revised: 17 July 2017 / Accepted: 18 July 2017 / Published: 21 July 2017
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This study demonstrates for the first time abnormal electro-optic (EO) characteristics induced by electrohydrodynamics (EHD) in a polymer-dispersed liquid crystal (PDLC) film in the presence of a low-frequency (1 kHz) AC voltage. Large LC droplets (20−40 µm) buried in the film can be obtained after the illumination of one UV light with a weak intensity (~0.96 mW/cm2) for 12 h. This film exhibits abnormal EO features, including the transmittance’s decay at a high voltage regime at normal incidence and the conversion between polarization independence and polarization dependence for the transmittance-voltage curve at normal and oblique incidences, respectively, of which properties are different from those shown in traditional PDLC films with small droplets. The abnormal EO characteristics of the large-droplet PDLC at the high voltage regime are attributed to a strong scattering effect associated with the formation of the foggy LC droplets in the cell. This effect is induced by a vortex-like LC director field with a rotational axis normal to the cell substrates in each dome-like droplet of the cell at the high voltage regime. The vortex-like director field is induced by a vortex-like turbulence of charged impurity generated by the EHD effect under the action of the AC electric field along the cell normal and the confinement of the dome-like boundary of the droplet on the charged impurities in each droplet. The scattering is decided by the degrees of mismatch between the refractive indices of the LC droplet and polymer, and the local fluctuation of the vortex-like director field in the droplet, resulting in the abnormal EO behaviors of the large-droplet PDLC. This investigation provides novel insight into the EHD effect in three dimensional (3D) microdroplets with anisotropic fluid. Such a large-droplet PDLC has potential in photonic applications, such as electrically controlled polarization-based optical components or optical converters between polarization independence and polarization dependence. View Full-Text
Keywords: polymer dispersed liquid crystal; liquid crystal droplet; electrohydrodynamics polymer dispersed liquid crystal; liquid crystal droplet; electrohydrodynamics

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Wu, S.-K.; Mo, T.-S.; Lin, J.-D.; Huang, S.-Y.; Huang, C.-Y.; Yeh, H.-C.; Chen, L.-J.; Lee, C.-R. Electrohydrodynamics-Induced Abnormal Electro-Optic Characteristics in a Polymer-Dispersed Liquid Crystal Film. Crystals 2017, 7, 227.

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