Fotoporządkowanie : alternatywna technika dla szybkich przetworników ciekłokrystalicznych

• Autorzy: Chrzanowski M. M. , Zieliński J. , Nowinowski-Kruszelnicki E. , Olifierczuk M.

Warianty tytułu

EN

Photoalignment : an alternative aligning technique for fast liquid crystal shutter

• Języki publikacji: PL

Abstrakty

PL

W artykule podjęto temat wyboru techniki fotoporządkowania ciekłego kryształu. Technologia ta jest alternatywą dla najczęściej stosowanego rubbingu, czyli jednostronnego polerowania warstw poliimidowych i poliamidowych. Zarówno w przypadku rubbingu (buffingu), który ma naturę kontaktową, jak i bezkontaktowego fotoporządkowania efektem pracy jest wytworzenie anizotropii warstwy, która następnie ma za zadanie porządkować leżącą bezpośrednio na niej warstwę ciekłego kryształu (LC). Rubbing jest metodą stosunkowo prostą i tanią i jest zwyczajowo używany przy produkcji wyświetlaczy ciekłokrystalicznych. W trakcie polerowania mogą jednak powstawać uszkodzenia struktury matrycy aktywnej oraz tworzyć się pyły, które są szkodliwe zwłaszcza dla bardzo cienkich warstw ciekłego kryształu. W związku z tym poszukuje się metod alternatywnych porządkowania. Z fotoporządkowaniem mamy do czynienia wtedy, gdy anizotropia warstwy porządkującej wywołana jest przez ekspozycję materiału fotoczułego na działanie światła ultrafioletowego spolaryzowanego liniowo. Jest to proces bezkontaktowy, więc eliminuje on większość wymienionych wcześniej wad rubbingu. Ponadto umożliwia pracę na plastycznych oraz zakrzywionych podłożach. Istnieją cztery różne drogi realizacji procesu fotoporządkowania warstwy światłoczułych materiałów organicznych: 1) fotodegradacja w materiałach poliimidowych, 2) izomeryzacja cis-trans azozwiązków, 3) czysta reorientacja związków azowych w polu potencjału światła UV oraz 4) sieciowanie w strukturze polimerowej. W pracy przedstawiono krytyczny przegląd wyżej wymienionych metod. Zastosowanie fotoporządkowania badane jest pod kątem przydatności w komórkach działających w oparciu między innymi o efekty: FLC (ang. ferroelectric liquid crystal, ciekły kryształ ferroelektryczny), TN (ang. twisted nematic, skręcony nematyk), BTN (ang. bistable twisted nematic, bistabilny skręcony nematyk), VAN (ang. vertical alignment nematic, pionowa deformacja fazy nematycznej), IPS (ang. in plane switching, przełączanie w płaszczyźnie) i inne. Celem poniższej pracy jest porównanie i określenie przydatności różnych metod fotoporządkowania dla technologii przetworników ciekłokrystalicznych o dużej jasności zobrazowania.

EN

In this study we consider the topic of the photoalignment of liquid crystal material. It is an alternative method to the rubbing of polyimide and polyamide layers. Both techniques provide the anisotropy in organic layers. This anisotropy aligns overlaying liquid crystal. The rubbing is a well known and cheap technique and it's ordinarily used in liquid crystal displays manufacturing. However, it has several disadvantages, for example it produces dust particles and charges the layer. Furthermore it may damage the surface electronic. These drawbacks can be critical factors in working with thin liquid crystal layers (about 2-5 µm) for example ferroelectric and antiferroelectric Lcs. Heterogeneity at the microscopic level can be noxious especially in the area of some types of liquid crystals and in manufacturing high-resolution liquid crystal displays (over 40”) and state-of-art projector display systems. In order to omit these problems, very important for the future work is to develop a new, universal and high-performance, technique for liquid crystal aligning. One of alternatives is photoalignment. It eliminates many of drawbacks mentioned above. This technique uses light (generally linearly polarized ultraviolet light, LPUV) to produce anisotropy in photodephiniable materials. In addition this technique allows us to obtain layers on plastic or curve surfaces. We can distinguish four main photoalignment mechanisms (including photo-chemical reactions and photo-physical changes): (1) cis-trans isomerization in azo-structures: pure dyes films, polymers containing azo-groups and monolayers of azodyes, (2) pure reorientation of photo-chemically stable azo-dyes molecules, (3) photodegradation in polyimide materials and (4) crosslinking in cinnamoyl and coumarin side-chain polymers. There are some modifications among these procedures, such as polymerizable azo-dyes or Langmuir-Blodgett films. Photoalignment is investigated in diverse liquid crystal modes, such as: twisted nematic (TN), vertical alignment (VAN), in plane switching (IPS) and many others. In this paper we describe all of the photoalignment mechanisms mentioned above and compare their ability to align the liquid crystal material in the field of application in various modes of LC cells.

Słowa kluczowe

PL

fotoporządkowanie; izomeryzacja cis-trans; sieciowanie krzyżowe; fotodegradacja; model dyfuzyjny; LCD; wyświetlacz ciekłokrystaliczny; LPP; fotopolimeryzacja liniowa; LPUV; światło ultrafioletowe spolaryzowane liniowo; LC; ciekły kryształ

EN

photoalignment; cis-trans isomerization; diffusion model; photodegradation; crosslinking; LCD; LPP; LPUV; LC

• Wydawca: Wojskowa Akademia Techniczna im. Jarosława Dąbrowskiego
• Czasopismo: Biuletyn Wojskowej Akademii Technicznej
• Rocznik: 2010
• Tom: Vol. 59, nr 3
• Strony: 375--394
• Opis fizyczny: Bibliogr. 73 poz., tab.

Twórcy

autor

Chrzanowski M. M.

autor

Zieliński J.

autor

Nowinowski-Kruszelnicki E.

autor

Olifierczuk M.

• Wojskowa Akademia Techniczna, Wydział Nowych Technologii i Chemii, Instytut Fizyki Technicznej, 00-908 Warszawa, ul. S. Kaliskiego 2

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