| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 105 === The mechanical rubbing process is a common approach to obtain homogeneous alignment for liquid crystals (LCs) because of its simplicity, thermal stability and low-cost. However, the mechanical damages could be generated through such a contact process to degrade the display performances and production yields. Hence, in the past decades, several non-contact alignment techniques have been studied and developed widely. In 2005, Sharp has successfully demonstrated a non- contact solution to align LCs vertically in a nanoparticle doped LCs (NPdLCs). The NPs can spontaneously adhere onto the substrates to generate vertical alignment anchoring due to their special structures. The manufactures can omit the LC alignment processes to enhance the production rate.
In this thesis, the feasibility to approach a variety of LC alignments in ionic nanoparticle doped LCs (INPdLCs) has been successfully demonstrated. The LC alignments generated by INPs are strongly dependent on the concentration of the INPs and the temperature of INPdLCs. As the sample of INPdLCs is heated to the temperature higher than its clearing temperature, the diffusion rate of INPs toward the indium-tin-oxide (ITO)-coated substrates is relatively high because of the low viscosity of the LC mixture. Accordingly, considerable INPs do randomly adhere onto the ITO-coated substrates to produce random alignment anchoring. The LC multi-domains generate due to the massive accumulation of disordered INPs adhered onto the ITO-coated substrates. Hence, the incident lights are scattered because they encounter different refractive indices of each LC domain through whole LC bulk. On the other hand, as the temperature of the INPdLCs sample is lower than its clearing temperature, the diffusion rate of INPs toward the substrates is relatively low. The INPs can homogeneously adhere onto the ITO-
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coated substrates and produce uniformly vertical alignment anchoring.
Furthermore, different LC alignments can be obtained as the INPs adhere onto different coatings, such as polyimide, PVA, etc., onto the ITO-coated substrates. The INPs generate the homogeneous alignment force as they adhere onto the substrates coated with unidirectionally rubbed polyimide. Interestingly, the angle between the homogeneous alignment anchoring and the rubbing direction of polyimide/PVA was experimentally measured to be about 10o. A model will be given to elucidate the experimental results in this thesis. Moreover, the electrochemistry of the INPdLCs was also investigated. Each INP is composed of one positive ion and one negative ion. They can be separated as a suitable DC voltage is applied. The positive (negative) ions diffuse across the bulk and adhere onto the negative (positive) electrode to produce vertical alignment anchoring, generated by the long side-chain of the positive and negative ions. In other words, the initially homogeneous LC alignment can be electrically switched to vertical one. The proposed results have also been confirmed according to the direct evidences obtained by mass spectrometry.
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