| Homogeneously Aligned Nematic Liquid Crystals Obtained by In Situ Polarized Visible Light and Subsequent RM-Stabilization with UV light |
| کد مقاله : 1212-ICOC |
| نویسندگان |
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ابوذر نصرالهی *، طیبه ناصری دانشگاه رازی کرمانشاه |
| چکیده مقاله |
| Liquid crystal (LC) orientation along the uniaxial direction is absolutely crucial in field of LCs, particularly to manufacture the high-quality liquid crystal display (LCD) such as TV, smartphone and so on. Photoalignment as a non-contact technique has already become popular because of its advantages compared to traditional rubbing method. The common process for LC alignment is to use the polymer based material like polyimide as pretreated substrates. However, several studies have recently been done without applying additional pretreatment for both planar and homeotropic LC alignment [1-5]. In this study, we demonstrate a uniform and stable homogenous alignment of nematic liquid crystals without using additional pretreatment of substrate by employing two separate visible and UV wavelengths for alignment and stabilization process, respectively. To achieve the proposed study, a series of azo-dye compounds that have restriction in miscibility to LC host due to the existence of polar end group, were doped in LC and examined by visible light. Figure 1 displays a group of azo-benzene compounds used for the study. It includes chrysophenine (CP), congo red (CR), acid yellow 9 (AY9), methyl orange (MO), and metanil yellow (MY). The common features of the dyes are extended π-conjugation of azo-benzene chromophore and polar substituents in the periphery of the core. Among them, chrysophenin was selected because of exhibiting the better alignment compare to others and as a visible-light-sensitive azo-dye compound has been added to the LC host (Δε > 0) to achieve in situ uniform planar alignment by employing polarized visible light. Electro-optical cells have been assembled by using the ITO (Indium-Tin-Oxide) glass plates and 10 µm cell gaps with no alignment layer. The mixture of dye doped LC which has been loaded to the cells showed random planar anchoring of LC molecules on inner surfaces of the cells. Those cells have been irradiated with linearly polarized visible light with suitable wavelength at the temperature few degrees above the nematic-isotropic transition temperature of the LC for 20 minutes. After treatment, the cell has been cooled down to room temperature and transition from random planar to uniform planar has been observed. To stabilize the alignment, the LC cell with reactive mesogen (RM) has been irradiated by UV light. Those cells with and without RM-stabilization have been examined against the heat and light treatment. Scheme 1 illustrates the schematic process of the PI-less in situ photoalignment. The in situ formation of stable alignment layer with no need of pretreatments for LC alignment provides a great potential for practical device applications. Work details will be discussed in the presentation. |
| کلیدواژه ها |
| photoalignment, nematic liquid crystals, visible-light-sensitive dye, reactive mesogen |
| وضعیت: پذیرفته شده |