Yazar "Kocakulah, Gulsum" seçeneğine göre listele

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    Comparison of electro-optical and dielectric properties of cobalt (II) phthalocyanine doped cholesteric liquid crystals
    (Elsevier, 2023) Kocakulah, Gulsum
    The aim of this study is to investigate and compare the electro-optical and dielectric properties of cobalt (II) phthalocyanine (CoPc) doped cholesteric liquid crystal (CLC) composites. Experimentally, pure CLC and CoPc (at different concentrations) doped CLC composites were produced. The wavelength-dependent transmittance behaviour of the samples was observed in Planar (P)-state without voltage and Focal Conic (FC)-state at low frequency with applied voltage. The P and FC states correspond to the transmitted and scattered of the incident light, respectively. Accordingly, the samples were transparent in P-state and opaque in FC-state. Furthermore, dielectric characteristic of pure CLC and CoPc doped CLC composites were investigated depending on the fre-quency. It was observed that dielectric constants and dielectric anisotropy changed with CoPc concentration in the low frequency region. Based on the electro-optical and dielectric properties, it is thought that produced CoPc doped CLC composites will be beneficial for optoelectronic devices.
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    Conductivity and optical bandgap parameters variations of methyl red-doped 4-pentyl-4'-cyanobiphenyl nematic liquid crystal: norland optical adhesive 65 photopolymer composites
    (Springer, 2023) Kocakulah, Gulsum; Koysal, Oguz
    In this study, the effect of methyl red (MR) concentration variation on conductivity and optical bandgap parameters of 4-pentyl-4'-cyanobiphenyl (5CB) nematic liquid crystal and norland optical adhesive 65 (NOA65) photopolymer (5CB:NOA65) composite was investigated. As a result of the experimental studies, wavelength-dependent absorbance, frequency-dependent dielectric constants (epsilon' and epsilon''), and alternating current (ac) conductivity (sigma(ac)) graphs of the samples were obtained. Also, dielectric anisotropy (Delta epsilon'), direct current (dc) conductivity (sigma(dc)), and optical bandgap (E-g) parameters were determined. It was observed that epsilon', epsilon'', and rac increased with increasing MR concentration at low frequency region. On the other hand, it was concluded that Delta epsilon' and E-g decreased with increasing MR concentration. It has been seen that the results are compatible with each other and it is thought that composites may be useful for liquid crystal-based devices.
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    Determination of optical band gap, transmittance, and dielectric constant parameters of Indium Phosphide/Zinc Sulfide quantum dot doped cholesteric liquid crystals
    (Elsevier, 2024) Kocakulah, Gulsum; Koysal, Oguz
    Nanomaterial doped cholesteric liquid crystal (CLC) composites have become important due to the improvement of their physical properties recently. In this study, the change of Indium Phosphide/Zinc Sulfide (InP/ZnS) quantum dot (QD) concentration in the optical, electro-optical, and dielectric parameters of CLC was examined. Voltage dependent transmittance and response time parameters were determined by the electro-optical switching method. Moreover, wavelength dependent absorbance and transmittance values of samples were investigated Ultraviolet/Visible (UV/VIS) spectroscopy. Dielectric parameters were examined with dielectric spectroscopy. Considering the experimental results, threshold voltage (Vth), response time (tau R), and optical band gap (Eg) values of CLC decreased with InP/ZnS QD contribution. On the other hand, dielectric constants (epsilon ' and epsilon ') and ac conductivity (sigma ac) values increased with InP/ZnS QD contribution at low frequencies. Furthermore, voltage dependent transmittance data indicated that samples were transparent in the absence of voltage (planar -state) due to transmission of light and opaque in the presence of certain voltage (focal conic -state) due to scattering of light. Results show that InP/ZnS QD causes considerable changes in the physical parameters of CLC and the produced samples can be used in the technological devices, especially light shutters.
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    A double-layer light shutter consisting of polymer dispersed liquid crystal and azo dye/quantum dot
    (Elsevier, 2024) Koysal, Oguz; Gleeson, Helen F.; Kocakulah, Gulsum
    We have developed a double-layer liquid crystal light shutter and investigated its temperature dependent morphological, electro-optical, and dielectric properties. The optical layers of the shutter are in direct contact, reducing optical losses. The shutter comprises a polymer dispersed liquid crystal film adjacent to an azo dye methyl red and CdSeS/ZnS quantum dot doped cholesteric liquid crystal layer. This novel double-layer light shutter device is switchable between opaque and transparent states at room temperature, and it exhibits low threshold and saturation voltages. Both the threshold (Vth) and saturation (Vsat) voltages are found to decrease with increasing temperature. The electrical characteristics of the shutter, namely the real part of dielectric constant (epsilon ') and the ac conductivity (sigma ac) also increase with temperature in the low frequency region. Our results show that this double-layer light shutter has interesting potential for simple electro-optical devices and smart window applications.
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    Effect of CdSeS/ZnS quantum dot concentration on the electro-optical and dielectric properties of polymer stabilized liquid crystal
    (Elsevier, 2020) Kocakulah, Gulsum; Algul, Gulay; Koysal, Oguz
    Our research paper has been discussed electro-optical and dielectric characterization of polymer stabilized liquid crystal (PSLC) and its doped form with different concentration of CdSeS/ZnS quantum dot (QD). PSLC composite was prepared using a nematic liquid crystal (E63) and Poly(methyl methacrylate) (PMMA) polymer. In order to improve physical properties, composites were dispersed with different concentration of CdSeS/ZnS QD. The electro-optical and dielectric properties of the composites were investigated depending on the frequency and voltage. Considerable physical parameters such as threshold voltage, dielectric anisotropy, relaxation frequency and response time were obtained from the experimental data. The results show that QD contribution and polymer networks change the electro-optical and dielectric properties of PSLC and these can become a focus of interest for new applications of PSLC composites in the future. (C) 2019 Elsevier B.V. All rights reserved.
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    Effect of intermolecular charge transfer between Ni(II)Pc and CdSeS/ZnS QD on dielectric relaxation mechanism of 5CB nematic liquid crystals in the presence of UV illumination
    (Springer, 2020) Kocakulah, Gulsum; Yildirim, Mert; Koysal, Oguz
    This paper is a report on electro-optical and dielectric parameters of Ni(II)Pc (nickel(II) phthalocyanine) and CdSeS/ZnS (cadmium selenide sulfide/zinc sulfide) quantum dot (QD) doped 5CB (4-pentyl-4 '-cyanobiphenyl) nematic liquid crystal (LC) in the dark and under UV illumination condition. Electro-optical and dielectric measurements of the samples were carried out using electro-optical switching and dielectric spectroscopy methods, respectively. Dielectric anisotropy, relaxation frequency, dielectric strength, and threshold voltage values were determined using the experimental data. Investigation of dielectric properties demonstrates that relaxation frequency is decreased because of the dispersal of Ni(II)Pc and CdSeS/ZnS QD under UV exposure. The electro-optical investigation also shows that UV illumination and dispersal of Ni(II)Pc and CdSeS/ZnS QD cause a decrease in threshold voltages. Overall, results indicate that Ni(II)Pc, CdSeS/ZnS QD and UV light enhanced the electro-optical and dielectric properties of 5CB nematic LC.
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    Electro-optical Performance Investigation of Cholesteric Liquid Crystal Containing Azo Dye: Light Shutter Device Application
    (Springer, 2021) Kocakulah, Gulsum; Koysal, Oguz; Kahyaoglu, Aliye
    In this study, the effect of chiral dopant concentration on electro-optical and dielectric properties of a cholesteric liquid crystal (CLC) composite was investigated, and a dye-doped cholesteric liquid crystal (DDCLC) light shutter was developed. The electro-optical properties of samples were investigated by electro-optical switching method without the use of a polarizer. The dielectric characterization of the composites were also realized using dielectric spectroscopy technique with a wide frequency range. Significant electro-optical and dielectric parameters, such as transition voltages, complex dielectric constant, dielectric anisotropy and light transmission values of composites were found from the experimental data. The obtained results show that the chiral dopant causes changes in electro-optical and dielectric parameters of CLC, and the developed DDCLC light shutter can be used in optoelectronic device applications.
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    The Fluorescent Materials Effect on Physical Parameters of Nematic Liquid Crystals
    (Springer, 2023) Kocakulah, Gulsum; Koysal, Oguz
    This study presents the physical properties of fluorescent material-doped E7 nematic liquid crystals (NLC). Indium phosphide/zinc sulfide (InP/ZnS) quantum dots and rubrene dye were preferred as fluorescent materials. In order to examine the effect of different fluorescent materials on the physical properties of E7 NLC, the phase transition temperatures, wavelength-dependent absorbance values, and the electro-optical and dielectric parameters of composites were determined. The obtained results showed that both InP/ZnS quantum dots and rubrene dye change the electro-optical and dielectric properties of E7 NLC. According to this, it is thought that fluorescent material-doped NLC composites could become a focus of interest for future electro-optical device applications.
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    Influence of UV light intensity on dielectric behaviours of pure and dye-doped cholesteric liquid crystals
    (Springer, 2020) Kocakulah, Gulsum; Yildirim, Mert; Koysal, Oguz; Ercan, Ismail
    This study aims to explore the ultraviolet (UV) light effects on dielectric properties of azo dye methyl red (MR)-doped cholesteric liquid crystal (CLC) composite. The CLC composite formed in the study contains 5CB nematic liquid crystal (LC) and S811 chiral additive. To obtain CLC/MR composite, CLC was dispersed with 2% wt/wt MR azo dye. Dielectric measurements of the CLC and CLC/MR samples were performed using dielectric spectroscopy technique in wide frequency range in the absence of UV light and at various UV light intensities (30, 60 and 90 mW/cm(2)) for 0 and 40 V. It was observed that the dielectric constant increased with UV light at low-frequency values. Dielectric loss data were utilized to extract relaxation frequency which was observed to increase with UV light exposure. Dielectric anisotropy of CLC sample exhibited typical transition from p-type to n-type, but this behaviour disappears for CLC/MR composite above 60 mW/cm(2) UV light intensity. Cole-Cole plots were used for extraction of dielectric relaxation data and obtained results showed that CLC sample shows Debye type relaxation only at 0 V whereas CLC/MR composite exhibits non-Debye type relaxation both at 0 V and 40 V. Moreover, conductivity properties of the samples were also investigated, and dc conductivity values were extracted from experimental ac conductivity values. It was found that MR incorporation increased dc conductivity, also it was significantly increased by UV light exposure and thus similar effect was also observed in current-voltage characteristics of the samples. The results show that azo dye MR molecules are suitable for CLCs since they lead to some enhancements in dielectric and electrical properties.