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Sudarshan Kundu,VIJAYKUMAR BALIYAN,이승희,강신웅 한국정보디스플레이학회 2015 Journal of information display Vol.16 No.1
Reported herein are the simultaneous phase and anchoring transitions of the chiral azodye-doped liquid crystal (LC) mixture. The transitions are influenced by photostimulation and are stable against light and thermal treatments. The photochromic trans state of the azobenzene molecule used in the study is mesogenic with a chiral nature. The photoinstigated cis form of the molecule has a much-enhanced dipole moment with a broken chromophore symmetry. Due to the high dipole–dipole interaction, the cis-state molecules stack together and form nano-sized aggregates. Subsequently, the cis aggregates get phase-separated, resulting in the chiral- to achiral-phase transition of the host LC. The phase-separated cis aggregates diffuse to the interface between indium-tin-oxide and LC and modify the surface, causing planar to homeotropic anchoring transition of the host LC. The stability and irreversibility of the transition, and the fact that there is no need for pre-treatments for LC alignment, provide a fascinating opportunity for LC device applications.
Sudarshan Kundu,Taponita Datta (nee Ray),Prasenjit Nayek,Tapas Pal Majumder,Subir Kumar Roy 한국물리학회 2008 Current Applied Physics Vol.8 No.5
Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC* phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (TC) from SmC* – SmA phase. The results have been discussed. Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC* phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (TC) from SmC* – SmA phase. The results have been discussed.
Kundu, Sudarshan,Lee, Myong‐,Hoon,Lee, Seung Hee,Kang, Shin‐,Woong WILEY‐VCH Verlag 2013 ADVANCED MATERIALS Vol.25 No.24
<P><B>In situ homeotropic alignment is achieved by photochromic <I>trans</I>‐ to <I>cis</I>‐isomerization</B> of an azo‐dye doped in a nematic host. The augmented dipole moment of the <I>cis</I>‐isomer formed under UV‐irradiation expedites molecular assembly into crystalline aggregates. Subsequent deposition of the aggregates creates a roughened surface and induces an anchoring transition from the initial planar to a homeotropic alignment of the LCs.</P>
Yang Liu,임영진,Sudarshan Kundu,이승희,이기동 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.6
The application of a single-wall carbon-nanotube (SWCNT) and polyimide (PI) composite thinfilm on an indium tin-oxide (ITO) glass substrate, working as the command surface in a twistednematic liquid crystal display (LCD), is described. SWCNTs were chopped and oxidized in a strongacid medium to make them more miscible in a polyimide solution. A film of this newly-developed PISWCNTcomposite was rubbed to determine the director direction for the LC molecules. The newlyfabricatedcommand surface was examined using a laser beam profiler and atomic force microscopy. Sizes of shortened SWCNTs were characterized by using field-emission scanning electron microscopy(FE-SEM). Finally, small-sized test panels were fabricated from this composite-coated ITO glass,and their electro-optic performances were measured. Although the operating voltage to switch acell was increased by around 41%, the switching speed was improved remarkably. The rise time ofthe test cells was found to be improved by around 10.12% and the decay time by around 29.77%. Thus, an overall improvement of around 16.12% in the total switching time was achieved. Thechange in the surface morphology of the newly-developed composite materials was found to be oneof the factors responsible for the faster switching of the device. Detailed discussions are given inthis report to explain the faster switching of the newly-developed twisted nematic liquid crystaldisplay (TN-LCD). The device can be useful for practical applications.
Taponita Datta (nee Ray),Sudarshan Kundu,Prasenjit Nayek,Tapas Pal Majumder,Subir Kumar Roy,W. Haase 한국물리학회 2009 Current Applied Physics Vol.9 No.3
We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (PS) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of PS of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (PS). An additional collective mode has been observed in the SmC* phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of PS in the isomeric mixtures. The result has been discussed. We report here the dielectric relaxation spectroscopy and electro-optical properties of a ferroelectric liquid crystal (FLC) CB470 (R) and isomeric mixtures containing CB470 (R) and its optical isomer CB480 (S) in two different concentrations. We have studied with two isomeric mixtures: mixing CB470 (R) and CB480 (S) in the ratio 95:5 (w/w) and 90:10 (w/w). With increase of percentage of CB480 (S) in the mixture the spontaneous polarization (PS) value has been decreased due to cancellation of a part of the dipolar contribution, since the direction of PS of the two isomers are in opposite direction. The tilt angles of the pure FLC materials and the isomeric mixtures remain almost unchanged. The dielectric strength of Goldstone mode is almost proportional to the spontaneous polarization (PS). An additional collective mode has been observed in the SmC* phase due to the formation of domain with large periodicity in pure FLC material and in one of the isomeric mixtures by unwinding the helical structures, which is known as domain mode. The existence of domain mode has been studied extensively with the variation of PS in the isomeric mixtures. The result has been discussed.