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1

Security devices based on liquid crystals doped with a colour dye

Carrasco-Vela C., Quintana X., Otón E., Geday M. A., Otón J. M.

Opto-Electronics Review

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2011

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Vol. 19, No. 4

495-500

EN

Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices. Employing liquid crystal and dichroic colorants, we have developed devices that show, with the aid of a polarizer, multiple images on each side of the device. Rubbed polyimide is used as alignment layer on each substrate of the LC cell. By rubbing the polyimide in different directions in each substrate it is possible to create any kind of symbols, drawings or motifs with a greyscale; the more complex the created device is, the more difficult is to fake it. To identify the motifs it is necessary to use polarized light. Depending on whether the polarizer is located in front of the LC cell or behind it, different motifs from one or the other substrate are shown. The effect arises from the dopant colour dye added to the liquid crystal, the induced orientation and the twist structure. In practice, a grazing reflection on a dielectric surface is polarized enough to see the effect. Any LC flat panel display can obviously be used as backlight as well.

2

Spectral and orientational properties of new group of naphthalene derivatives of bicarboxylic acid in liquid crystal 7CB

Bielejewska N., Wolarz E., Stolarski R., Bauman D.

Opto-Electronics Review

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2008

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Vol. 16, No. 4

367-374

EN

The spectral and orientational properties of some dichroic fluorescent dyes (naphthalene derivatives of bicarboxylic acid) in some isotropic solvents and in an anisotropic matrix have been studied. The order parameter of the dyes in the nematogenic liquid crystal 7CB has been determined from measurements of polarized electronic absorption and fluorescence. The influence of the dye addition on the nematic-isotropic phase transition temperature of 7CB has been investigated. It was found that some of the dyes studied could be successfully utilized in guest-host liquid crystal display devices.

3

Orientational behaviour of some homologues of 4-n-pentyl-phenylthio-4'-n-alkoxybenzoate doped with dichroic dye

Bauman D., Zięba A., Mykowska E.

Opto-Electronics Review

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2008

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Vol. 16, No. 3

244-250

EN

The long-range orientational order of three members of 4-n-pentylphenylthio-4'-n-alkoxybenzoate (nS5) series doped with a dichroic dye was studied by means of electronic absorption and fluorescence measurements. The order parameters and as well as the orientational distribution function were determined on the basis of absorption and emission spectra of linearly polarized light recorded as a function of temperature in the nematic, smectic A, and smectic C phases. An influence of the dye molecular structure on the orientational order of the dye/liquid crystal mixture was observed. Moreover, the dependence of the order parameter values on the length of the alkoxy chain in liquid crystal molecules was found. It was shown that the order parameter , obtained from fluorescence measurements, can be helpful in recognizing the second-order or weakly first-order transitions between various liquid crystalline phases.

4

Problem of light propagation in real TN display

Zieliński J., Olifierczuk M.

Biuletyn Wojskowej Akademii Technicznej

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2002

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Vol. 51, nr 1

77-92

EN

In this paper we present the results of our analysis of the light passing through a TN display operating in real conditions. We have proposed a structure of a TN display which allows analysing its optical parameters in conditions similar to the real ones. Basing on this structure we have done a mathematical analysis of the light propagation through a display. Mathematical analysis made it possible to work out a computer program. This program calculates optical parameters of a display, such as contrast ratio, luminance in both states (on and off) and colour co-ordinates of an image. Using this program we have analysed an influence of properties of all elements of a display's optical parameters.

PL

Praca ta prezentuje wyniki przeprowadzonej analizy transmisji światła przez displej TN pracujący w warunkach rzeczywistych. Zaproponowana została struktura displeja do analizy, umożliwiająca dostatecznie dobre przybliżenie rzeczywistych warunków pracy przetwornika. W oparciu o tę strukturę dokonano matematycznego opisu propagacji światła przez displej. Opis ten był podstawą do opracowania programu komputerowego modelującego pracę przetwornika TN. Program ten umożliwia uzyskanie wyników takich jak współczynnik kontrastu optycznego, luminacja w obu stanach (włączonym i wyłączonym) oraz ich współrzędnych barwnych. Posługując się opracowanym programem dokonano analizy wpływu poszczególnych elementów displeja na jego parametry optyczne.

5

The order parameter of liquid-crystalline mixture with dichroic dye for TN LCD

Olifierczuk M., Kędzierski J., Raszewski Z., Zieliński J., Miszczyk E.

Biuletyn Wojskowej Akademii Technicznej

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1999

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Vol. 48, nr 4

99-106

EN

Paper contains results of studies on TL LC mixture with a black dichroic dye. The general information concerning a principle of an action of TN display with the dye is presented. The effect of the dye on temperature dependence of LC order parameter is discussed. The order parameter is confirmed by several methods (Lorentz-Lorenz's, Vuks-Chandrasekhar-Madhusudana's, Neugebauer-Saupe-Maier's procedures and extrapolation by Haller and Subramhanyam) for PCB.

PL

Praca zawiera wyniki badań nad efektem TN z czarnym barwnikiem dichroicznym. Podane są ogólne informacje na temat zasady działania displeja TN z barwnikiem chroicznym. Przedyskutowano wpływ barwnika na temperaturową charakterystykę parametru uporządkowania warstwy. Parametr uporządkowania otrzymano różnymi metodami (procedury Lorentz-Lorenz, Vuks-Chandrasekhar-Madhusudana, Neugebauer-Saupe-Maier i ekstrapolacje Hallera i Subramhanyamy) i sprawdzono dla PCB.