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1

The molecular dynamics of nematic liquid crystal confined in porous membranes treated by different surfactants

Różański Stanisław Andrzej

Opto-Electronics Review

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2019

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Vol. 27, No. 4

339--344

EN

The molecular dynamics of the well-known nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl geometrically restricted in Anopore and Synpor porous membranes with various pore structure and treated by different surfactants (namely decanoic acid and lecithin) is compared. In the Anopore membrane the chosen surfactants induce the homeotropic orientation of the molecules on the walls of the cylindrical pores and observed corresponding relaxation processes (librational modes) are practically the same. The dielectric measurements of lecithin treated Synpor membranes reveals the reorientation of the molecules from planar to homeotropic on the complex multilayer structure present in their volume. The dielectric strengths of the observed two molecular processes (δ-process and librational mode) are inversed in the ratio compared to the untreated membranes. The observed differences in molecular dynamics results from the orientation of the liquid crystal molecules in untreated and treated membranes and the structure of the membranes themselves.

2

Dispersion of fluorescent dye in the nematic liquid crystal : enhanced photoluminescence and high birefringence

Pathak G., Agrahari K., Roy A., Srivastava A., Strzezysz O., Garbat K., Manohar R.

Opto-Electronics Review

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2018

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Vol. 26, No. 4

317--324

EN

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).

3

Analysis of birefringence property of three different nematic liquid crystals dispersed with TiO₂ nanoparticles

Pathak G., Katiyar R., Agrahari K., Srivastava A., Dabrowski R., Garbat K., Manohar R.

Opto-Electronics Review

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2018

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Vol. 26, No. 1

11--18

EN

In the present work TiO₂ nanoparticles (NPs) have been dispersed into three different nematic liquid crystals (2020, 1823A and 1550C) in different concentration. The value of the birefringence (Δn) has been calculated by the transmitted intensity method at a 632.8 nm wavelength. NLC 2020 used in the present study is a high birefringent material (Δn = 0.44), NLC 1550C is a low birefringent material (Δn = 0.067) and NLC 1823A is a mid birefringent material (Δn = 0.14). An increased value of birefringence has been found after dispersion of TiO₂ NPs in all three NLCs but this increment depends upon the concentration of the dopant material, temperature range and chemical character of the mixtures. It is suggested that this LC materials can be applicable in making of phase shifters, compensators and many more photonic devices.

4

Numerical investigation of influence of ionic space charge and flexoelectric polarization on measurements of elastic constants in nematic liquid crystals

Buczkowska M., Derfel G., Konowalski M.

Opto-Electronics Review

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2009

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Vol. 17, No. 2

95-98

EN

Deformations of nematic layers caused by magnetic field allow determination of the elastic constants of liquid crystal. In this paper, we simulated numerically the deformations of planar and homeotropic nematic layers. The flexoelectric properties of the nematic and presence of ions were taken into account. Our aim was to show the influence of flexoelectricity on the results of the real measurement of the elastic constants k33 and k11. In these simulations, we calculated the optical phase difference Δ Φ between the ordinary and extraordinary rays of light passing through the layer placed between crossed polarizers as a function of the magnetic field induction B. One of the elastic constants can be calculated from the magnetic field threshold for deformation. The ratio k33/k11 can be found by means of fitting theoretical ΔΦ(B) dependence to the experimental results. The calculations reveal that the flexoelectric properties influence the deformations induced by the external magnetic field. In the case of highly pure samples, this may lead to false results of measurement of the elastic constants ratio k33/k11

5

Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy I., Kurioz Y., Reznikov Y.

Opto-Electronics Review

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2009

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Vol. 17, No. 2

116-119

EN

We report on first studies of wetting of liquid crystal on photoaligning surface. We observed strong light-induced variations of a contact angle of a liquid LC 5CB on a photoaligning surface of fluoro-polyvinyl-cinnamate (PVCN-F) and we connected these variations with changes of PVCN-F polarity. We also present drastic changes of the contact angle of a nematic liquid crystal (MLC-6080) on the PVCN-F surface in a vicinity of temperature anchoring transition of liquid crystal from homeotropic orientation to planar one. We did not find any peculiarities in temperature dependence of the contact angle of isotropic liquid (glycerol) on PVCN-F and of nematic liquid crystal on pure glass in the same temperature range. It allows us to suggest that rearrangement of LC molecules and flexible fragments in the LC-polymer interface are responsible for the change of surface tensions both of LC and polymer and the observed jump of the contact angle.

6

Liquid crystal display as a spectral selection element for visible spectrometers

Hegde G. M.

Journal of Technical Physics

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2009

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Vol. 50, no 2

87-96

EN

In this paper, polarization property of twisted nematic liquid crystal display (TNLCD) was experimentally studied for its application as a wavelength selection element. Output from a white light emitting diode (LED) was separated into its constituent wavelengths, with a resolution of about 2-5 nm in proportion to the voltage applied to TNLCD. Its performance as a spectral selection element in visible spectrometer is experimentally demonstrated. A simple, inexpensive spectrometer design built around a LED and a TNLCD is proposed.

7

The kinetics of nucleation in inhomogeneous media based on the classical Avrami model

Rogowski R. Z.

Materials Science Poland

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2005

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Vol. 23, No. 4

961--969

EN

n this paper, the kinetics of nucleation is studied in inhomogeneous media such as a mixture of the nematic liquid crystals p-methoxybenzylidene-p-butylaniline (MBBA) and p-ethoxybenzylidene-p-n-butylaniline (EBBA). Experimental data are analysed in terms of the classical Avrami model for nucleation. The observed non-uniform nucleation is explained within the framework of the Landau model for phase transitions. A modification to the Avrami model is proposed in order to describe the kinetics of nucleation in highly inhomogeneous media.

8

Dielectric Relaxation and Viscosity of Mesogenic n-Heptylcyanobiphenyl

Ginovska M.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 10

1505-1511

EN

Molecular dynamics of n-heptylcyanobiphenyl (C7H15-Ph-Ph-C=N, 7CB) in the isotropic and nematic phases was studied with the use of dielectric spectroscopy. In the measuring frequency range (from 100 kHz to 100 MHz) the absorption band corresponding to the molecular rotation around the short axis dominates in the dielectric spectrum. On the basis of temperature dependences of the relaxation time and the shear viscosity of 7CB, the strength of the nematic potential and the effective length of the rotating 7CB molecule were estimated.

9

Investigation of electrooptical properties of supertwisted nematic efect for multibottle liquid crystal mixture system

Parka J., Żmija J., Dąbrowski R.

Journal of Technical Physics

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1998

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Vol. 39, no 2

205-211

EN

Electrooptical properties of supertwised nematic effect depend on material constants of liquid crystal technical parameters of display construction. Optimisation of these parameters for isothiocyanate and esters liquid crystals mixtures has been carried out. Some experimental results have been presented.