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Dielectric and electro-optical properties of zinc ferrite nanoparticles dispersed nematic liquid crystal 4’-Heptyl-4-biphenylcarbonnitrile
摘要： In this work, comprehensive results on dielectric and electro-optical properties of pristine and zinc ferrite (ZnFe2O4) nanoparticles (NPs) dispersed in host nematic 4?-Heptyl-4-biphenylcarbonnitrile (7CB) systems are reported. The dielectric and EO properties of pristine and NPs dispersed (concentrations 0.05, 0.1, 0.15, 0.2, 0.3 and 0.5 wt%) into the host nematic system have been studied. We have seen uniform NPs dispersion into nematic 7CB up to 0.15 wt% concentration of NPs by the POM. The NPs aggregation starts at 0.2 wt% dispersion. It is shown that the dielectric and electro-optical properties are strongly in?uenced by the concentration of NPs in host nematic and applied electric ?eld. The dielectric anisotropy is maximum for the NPs dispersed system of 0.15 wt% concentration. The Birefringence, parallel and perpendicular components of permittivity and conductivity are found to be dependent on temperature and concentration of NPs into host matrix. In pure nematic material, small memory is seen but in NPs dispersed systems noticeable memory is found. In particular, pronounced memory is found for the dispersed system of 0.3 wt% concentration of NPs.
关键词： Nematic liquid crystal,zinc ferrite nanoparticles,birefringence,splay elastic constant,dielectric anisotropy
更新于2025-09-12 10:27:22
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Investigation of dielectric and electro-optical parameters of high birefringent nematic liquid crystal doped with TiO <sub/>2</sub> nanoparticles and its applicability toward liquid crystal displays
摘要： In the present study, anatase TiO2 nanoparticles (NPs) have been doped in three different concentrations into nematic liquid crystal (NLC) 2020 (fluorinated 4’-alkylphenyl-4-isothiocyanatotolanes). The ratio has decreased and increased, response time and contrast respectively for the NLC-NPs composite system. Polarizing optical microscope images reveal that alignment has been improved after the doping of TiO2 NPs. Dielectric measurement study shows that the tan d has been decreased and relaxation frequency shifted toward the lower frequency region for the doped system. The outcome of the present investigation may be very useful in the improvement of electro-optical features of liquid crystal displays.
关键词： Nematic liquid crystal,response time,Contrast ratio,TiO2 nanoparticles
更新于2025-09-12 10:27:22
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State transition at electrohydrodynamic convection of twisted nematic liquid crystals
摘要： We study electrohydrodynamic convection (EHC) patterns in twisted nematic liquid crystal (TNCL) cells with an initial homeotropic alignment. In addition, we demonstrate switching characteristics due to the transition between the 90° and ?90? twisted states. The pattern formations are similar to those obtained in a parallel-aligned nontwisted liquid crystal cell. Calculations of the free energy in an initially, homeotropically aligned TNLC in an electric ?eld demonstrate that the energy barrier between the two states decreases with the increase of the electric ?eld. The mutual transition is caused by the ?uctuating ?ow at the dynamic scattering mode 2, where the energy barrier between the two states is reduced by applying a strong electric ?eld. These properties may be employed for the development of a redirectable dynamic lenticular lens, as an extended version of the dynamic lenticular lens using EHC. The transition between the two states caused by EHC is reversible, and the convection roll pattern of the Williams domain rotates by 90° at each transition.
关键词： state transition,homeotropic alignment,electrohydrodynamic convection,dynamic lenticular lens,twisted nematic liquid crystal
更新于2025-09-10 09:29:36
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Improvement of the third order nonlinear optical properties of nematic liquid crystal under the influence of different compositional percentage of doped SWCNT and the external electric field
摘要： In this research, the nematic liquid crystal (NLC) was doped with varying concentration (0-1 % wt.) of single walled carbon nanotubes (SWCNTs) at room temperature to study the nonlinear optical (NLO) properties of E5CN7@CNT cell.The third order NLO properties such as the nonlinear susceptibility, the nonlinear refraction (NLR) and the nonlinear absorption (NLA) were determined by using Z-scan techniques. The nonlinear studies have been done using a continuous wave (CW) He: Ne laser at 632.8 nm.Doping SWCNTs to eutectic uniaxial NLC (E5CN7) enhanced the third order nonlinear susceptibility, ??(3) and consequently the nonlinearity properties of composite systems improved.It is found that at lower concentration of CNTs (c< 0.75 % wt.), the third order nonlinear susceptibility are increased, but for concentration 0. 5<c<1 % wt., the third order nonlinear susceptibility are decreased. The negative sign of the observed NLR index, indicates that the E5CN7@CNT exhibits self-defocusing type optical nonlinearity. The two photon absorption (TPA) behavior, corresponding to negative sign NLA of samples. The reorientation of samples molecules amplifies upon the application of electric field, then nonlinearity increases.
关键词： Composite materials,Nematic liquid crystal,Carbon nanotubes,Third order nonlinear susceptibility,Nonlinear optics,Electric field,Z-scan method
更新于2025-09-10 09:29:36
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Cylindrical nematic liquid crystal shell: effect of saddle-splay elasticity
摘要： This study introduces cylindrical nematic liquid crystal (LC) shells. Shells as confinement can provide soft matter with intriguing topology and geometry. Indeed, in spherical shells of LCs, rich defect structures have been reported. Avoiding the inherent Plateau–Rayleigh instability of cylindrical liquid–liquid interfaces, we realize the cylindrical nematic LC shell by two different methods: the phase separation in the nematic–isotropic coexistence phase and a cylindrical cavity with a glass rod suspended in the middle. Specifically, the director configurations of lyotropic chromonic LCs (LCLCs) in the cylindrical shell and their energetics are investigated theoretically and experimentally. Unusual elastic properties of LCLCs, i.e., a large saddle-splay modulus, and a shell geometry with both concave and convex curvatures, result in a double-twist director configuration.
关键词： cylindrical nematic liquid crystal shells,lyotropic chromonic LCs,double-twist director configuration,saddle-splay elasticity
更新于2025-09-10 09:29:36
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Effective permittivity of liquid crystal nanodispersions and composites with different pore structure
摘要： The volume filling fraction dependence of the effective permittivity of the nematic liquid crystal 4-n-pentyl-4’-cyanobiphenyl embedded in different porous membranes and dispersed with aerosil nanoparticles was determined using broadband dielectric spectroscopy in the frequency range from 106 to 109 Hz. The experimental data were analyzed and compared with some existing theories based on the effective medium approximation and their modifications. The obtained effective permittivities as a function of the volume filling fraction lie between the lower limits of the Wiener and Hashin–Shtrikman bounds. The observed shift of the experimental points reflects the changes in the structure of the investigated composites.
关键词： Hashin–Shtrikman bounds,Dielectric spectroscopy,nematic liquid crystal,Maxwell Garnett theory,Wiener bounds
更新于2025-09-09 09:28:46
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Dispersion of fluorescent dye in the nematic liquid crystal: Enhanced photoluminescence and high birefringence
摘要： In the present investigation optical, electro-optical and dielectric properties have been measured for nematic liquid crystal (NLC) material 1550C which is consisted of 4’-(trans, trans-4-alkylbicyclohexyl) carbonates and 4’-(4-(trans,trans-4-alkyl)-4-cyanobicyclohexane, dispersed with fluorescent dye (Benzo 2,1,3 Thiadiazole) in two different concentrations. Photoluminescence has been enhanced for dye dispersed system which is the key finding of this investigation. UV absorbance study has also been performed and found to be increased for composite system. Enhanced birefringence after dispersion of dye into pure NLC is also a prominent result of this investigation. Relative permittivity, threshold voltage and dielectric anisotropy have also been measured and found to be increased. The outcome of the present work may be very useful in the construction of liquid crystal displays (LCDs).
关键词： Photoluminescence,Nematic liquid crystal,Fluorescent dye,Dielectric anisotropy,Birefringence
更新于2025-09-09 09:28:46
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Numerical Modeling of the Static Electric Field Effect on the Director of the Nematic Liquid Crystal Director
摘要： A two-dimensional model of the Frederiks effect is used to investigate the static electric field effect on the orientation of the nematic liquid crystal (LC) director in a side-electrode cell. The solutions are obtained by the standard finite-difference methods. The programs for the numerical solution of a two-dimensional parabolic partial differential equation are developed both in FORTRAN and C/C++. The Frederiks transition threshold for the central part of the cell and the dependences of the director’s orientation distribution on a high electric field are obtained. The results of the calculation are compared with the experimental data.
关键词： nematic liquid crystal,two-dimensional model of the Fredericks effect,finite-difference methods,electric field,director,numerical solution
更新于2025-09-09 09:28:46