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1

Recent trends in studies on polymer-dispersed liquid crystal composites

Kłosowicz Stanisław J.

Biuletyn Wojskowej Akademii Technicznej

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2019

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Vol. 68, nr 2

15--21

EN

The paper presents a review of results of studies in the field of PDLC material science and physics obtained during last few years and shows the main fields of interest in that subject. It covers an application of new polymers and liquid crystalline materials used to prepare those composites, modification of their properties by different inorganic and organic dopants as well as new optical properties. The evolution of scientific interest regarding PDLC composites in recent years is shown.

PL

W artykule przedstawiono przegląd wyników badań w zakresie inżynierii materiałowej i fizyki kompozytów ciekłokrystalicznych typu PDLC, otrzymanych w ciągu ostatnich czterech lat, oraz główne obszary zainteresowania w tym temacie. Obejmuje to zastosowanie nowych polimerów i materiałów ciekłokrystalicznych wykorzystanych do otrzymywania kompozytów, modyfikację właściwości kompozytów za pomocą różnych domieszek nieorganicznych i organicznych, jak również nowe właściwości optyczne PDLC. Wskazano na zmiany kierunków zainteresowań badawczych w ostatnich latach.

2

The comparison of electrooptical properties of PDLC liquid-crystalline composites in visual and near-IR ranges

Sułkowski K., Węgłowski R., Kłosowicz S.J.

Biuletyn Wojskowej Akademii Technicznej

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2017

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Vol. 66, nr 3

15--26

EN

Electrooptical properties of conventional Polymer-Dispersed Liquid Crystals (PDLC) composites were compared in visual and near-IR ranges for the electrically-induced light transmission effect. It was confirmed that the most important for the optical contrast value is the matching of refractive indices of the polymer matrix and dispersed droplets of liquid crystal, as well as matching droplet size and wavelength of incident radiation. The optimization of electrooptical parameters of such materials needs new liquid-crystalline mixtures dedicated for near-IR range. The studied effect can be applied for manufacturing window glasses with electrically adjusted transmission of infrared radiation.

PL

Porównano właściwości elektrooptyczne konwencjonalnych kompozytów typu PDLC (Polymer-Dispersed Liquid Crystals) w obszarze widzialnym i bliskiej podczerwieni dla przypadku efektu elektrooptycznego elektrycznie indukowanej transmisji światła. Potwierdzono, że na wartość współczynnika kontrastu optycznego najbardziej wpływa dopasowanie współczynników załamania matrycy polimerowej i zawieszonych w niej kropel ciekłego kryształu, jak również dopasowanie przeciętnego rozmiaru kropel i długości fali padającego promieniowania. Optymalizacja parametrów elektrooptycznych takich materiałów wymaga opracowania nowych mieszanin ciekłokrystalicznych przeznaczonych na zakres bliskiej podczerwieni. Badany efekt może być wykorzystany do wytwarzania szyb okiennych o elektrycznie regulowanej transmisji promieniowania podczerwonego.

3

Non-linear electrooptic effect in antiferroelectric liquid crystal

Dardas D., Kuczyński W., Hoffmann J., Jeżewski W., Nowicka K. K., Małecki J.

Opto-Electronics Review

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2009

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Vol. 17, No. 1

25-29

EN

Electrooptic phenomena caused by weak electric fields, much lower than those needed for the helix unwinding, in helical smectic liquid crystals were studied in thin planar samples. The investigations were performed in chiral liquid crystal 4-(1-methyl-heptyloxycarbonyl) phenyl 4'-(3-butanoyloxy propyl-1-oxy) biphenyl-4-carboxylate which exhibits antiferro-electric properties. We have found that electric field applied to a helical smectic liquid crystal caused two effects. First, the helix was deformed and the position of effective optic axis changed by an angle proportional to the field strength. The second effect, quadratic in field, causes the change in the shape of the indicatrix. As a consequence, the relative changes in the light intensity caused by external electric field consist of two components. The first component represents the modulation with the fundamental frequency and the second one with the doubled frequency (second harmonic of the electrooptic effect). The ab- solute values of the first- and second-order electrooptic coefficients have been determined and their temperature dependence discussed.

4

Interface effects on the NLO properties of guest-host materials

Makowska-Janusik M., Kassiba A. H., Failleau G., Boucle J.

Materials Science Poland

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2006

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Vol. 24, No. 4

891--900

EN

Electro-optical properties of silicon carbide (SiC) nano-sized clusters embedded into three different polymeric matrices, i.e., poly(methyl methacrylate, poly-N-vinylcarbazole and polycarbonate were investigated. Electric properties of SiC were calculated using time-dependent DFT methods considering an isolated cluster and environmental effects. The concept of the polymeric influence on optical properties of chromophores was executed by the local electric field approach. Electric field created by charge distribution of the surrounding polymer was calculated using guest-host structures obtained by the molecular dynamics simulations. Optical properties of SiC situated in polymeric environments differ from those of free clusters. It is seen more significantly for the hyperpolarizability than for the polarizability. The spatial distribution of SiC in the matrix depends on the kind of polymer and gives an important influence on the obtained local electric field value. The Si-C distances do not change with variation of the polymeric matrix. The geometry of 3C-SiC is very stable and does not change during MD simulations performed at 300 K.

5

Optical crystals survived in information technology systems

Miyazawa S.

Opto-Electronics Review

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2003

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Vol. 11, No. 2

77-84

EN

Different optical crystals are reviewed from the viewpoint of their optical properties, among which typical crystals survived in the recent information technology (IT) systems. Most of revived or survived crystals are somehow traditional ones because of their established properties. Potential applications of oxide crystals into shorter wavelengths are focused as additional ripple effects of the impetuous deployment of the IT. Some recent activities on developing new crystals are described briefly ; GdVO₄ with a large walk-off angle as a birefringent crystal, Y₂O₃ as a new laser host, periodically poled ferroelectric LiNbO₃ and LiTaO₃ crystals as effective devices of frequency conversion, and traditional sapphire as a potential substrate of GaN-LEDs.

6

Electrooptical properties of metal organic ionic liquid crystals

Klimusheva G., Koval'chuk A., Volynets N., Vakhnin A.

Opto-Electronics Review

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2002

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Vol. 10, No. 1

39-42

EN

Electrooptics of smectic liquid crystals has been drawing an increasing interest, especially for new classes of compounds, such as metal alkanoates which manifest as thermotropic as lyotropic smectic mesophases. In the present work, electric and electrooptic properties were studied in detail of pure and dye-doped (polymethine dye) potassium kaproate, a water mixture of which is forming a lyotropic Sm A type liquid crystalline phase at room temperature. As follows from experimental data, for frequencies - f < 3 x 10⁴ Hz, dispersion of the components of complex dielectric permittivity ε' and ε'' is observed. Appropriate relaxation process is described by the Debye equation. On the basis of the analysis of frequency dependencies of ε' ε'' for the frequencies f > 3 x 10⁴ Hz the conductivity of samples on an alternating current was found. The introduction of dye in ionic lyotropic liquid crystals (ILLC) results in increase in conductivity (by 1.5 times) and reduction of relaxation time. The bleaching of the dye in ILLC under the action of a direct voltage (U>5V) was observed. The mechanism explaining "threshold" character of such process was proposed.