Browsing by Author "Karapinar, R"

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Damping of the Twist Director Fluctuations in the Nematic Liquid Crystal
(Elsevier Science Bv, 1996) Karapinar, R
The spectrum of Rayleigh scattered light in the planar aligned nematic liquid crystal octyloxycyanobiphenyl is studied by means of an optical homodyne technique. Experimental values are reported for the damping times and visco-elastic ratios associated with the twist elastic distortions in the nematic region as a function of temperature. The results obtained are discussed in relation to currently available theories concerning the elastic and viscous properties of nematics. It turns out that the measured visco-elastic properties are in reasonable agreement with the theoretical predictions.
Electro-Optical Switching Properties of a Polymer Dispersed Ferroelectric Liquid Crystal Device
(Iop Publishing Ltd, 1998) Karapinar, R; O'Neill, M
A fast and high-contrast polymer dispersed ferroelectric liquid crystal (PDFLC) device was fabricated using a polymerization-induced phase separation technique which involves ultraviolet photopolymerization with an argon ion laser. The PDFLC film was oriented by the mechanical shear flow during the polymerization of an ultraviolet-curable adhesive. The switching times, contrast ratio and spontaneous polarization of the PDFLC film were investigated. The sample preparation parameters, such as the curing time and curing intensity were also reported.
Nano-Size Polymer Dispersed Liquid Crystals for Phase-Only Optical Modulation
(Taylor & Francis Ltd, 2002) Lucchetta, DE; Manni, A; Karapinar, R; Gobbi, L; Simoni, F
In this work we report the preparation details and the electro-optical characterization of a new class of nanometer-sized PDLC obtained by using a multifunctional monomer in a pre-polymer mixture which is suitable for fast polymerization process. A systematic analysis of the sample morphology has been carried out on a large number of samples characterized by different values of the photoinitiator concentration and curing parameters. These samples have high transparency to the visible light. However, reorientation of the liquid crystal domains due to the application of a suitable voltage can affect the optical phase shift making these materials suitable as polarization independent "phase only" optical modulators.
Phase-Only Modulation by Nanosized Polymer-Dispersed Liquid Crystals
(Amer inst Physics, 2002) Lucchetta, DE; Karapinar, R; Manni, A; Simoni, F
We report the preparation methods and electro-optical characterization of polymer-dispersed liquid crystals with nanosized liquid crystal domains obtained by using a multifunctional monomer in a prepolymer mixture that is suitable for a fast photopolymerization process. The electric-field-induced optical phase shift has been measured using a Mach-Zender interferometer, getting values up to pi/2 with an applied voltage of about 20 V/mum with no dependence on the light polarization. The high transmittance of the samples make them suitable for photonic devices and telecom applications. (C) 2002 American Institute of Physics.
Polymer Dispersed Ferroelectric Liquid Crystal Films With High Electro-Optic Quality
(Iop Publishing Ltd, 2002) Karapinar, R; O'Neill, M; Hird, M
Polymer dispersed ferroelectric liquid crystal (PDFLC) films are composite materials of a ferroelectric liquid crystal dispersed in the form of micron-sized droplets in a polymer matrix. In this study PDFLC films with a novel ferroelectric mixture were prepared by a polymerization-induced phase separation technique. The uniform orientation of the ferroelectric liquid crystal droplets was obtained by shearing during the phase separation process. The electro-optic characteristics of the films were analysed. Experimental results on response times. contrast ratio and spontaneous polarization were presented. Since these films exhibit high electro-optic quality, they have the potential of use in a wide range of display devices.