Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3820
標題: 循環式紫外光照射系統輔助乙醇合成扭曲向列型液晶分子保護奈米銀粒子之研究
Synthesis of Silver Nano-particles Protected with Twisted Nematic Liquid Crystal by Assisted with the Cyclic Ultraviolet Irradiation in Ethyl Alcohol
作者: 蘇品華
Sue, Pin-Hua
關鍵字: 向列型液晶
Twisted nematic liquid crystal
循環式
紫外光照射
光化學
乙醇還原法
奈米銀粒子
Cyclic process
Ultraviolet irradiation
Phoholysis
Ethyl alcohol reduction
Silver nano-particle.
出版社: 化學工程學系所
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摘要: 近年來,奈米材料被廣泛地應用,因具備小尺寸效應、表面效應等特性,而表現出新穎現象及特殊的性質,可應用於傳統工業、電子工業、光電科技及醫藥保健等方面。 本研究以高氯酸銀(AgClO4)為金屬前驅物,乙醇為還原劑並兼具溶劑,利用循環式紫外光還原系統合成奈米銀粒子,並加入向列型液晶(4''-n-pentyl-4-cyanobiphenyl, 5CB)當保護劑,改變曝光強度、高氯酸銀濃度與紫外光照光時間來控制奈米銀粒子之粒徑大小,藉由5CB液晶的保護可使奈米銀粒子均勻摻合於扭曲向列型液晶胞中。並進一步用UV-Vis、FTIR、XRD、ICP-AES及TEM等儀器作特性分析。當高氯酸銀濃度為0.05M、5CB/AgClO4莫耳濃度比為1、曝光時間為3小時及紫外光曝光強度提高至50 mW/cm2時,其奈米銀粒子之轉化率可提高至43%,平均粒徑為17 nm;當高氯酸銀濃度為0.01 M、紫外光曝光強度為25 mW/cm2、曝光時間為3小時及5CB/AgClO4莫耳濃度比增加至5時,則銀粒子的平均粒徑可降低至7.0 nm;當高氯酸銀濃度為0.05M、5CB/AgClO4莫耳濃度比為1及紫外光曝光強度為50 mW/cm2,則紫外光照光時間增長,可由紫外光-可見光吸收光譜儀中,得知反應終點為21小時左右,轉化率為76%。光電特性方面,以扭曲向列型液晶與奈米銀粒子混合,並探討奈米銀粒子在扭曲向列型液晶胞中之光電影響。實驗結果顯示:在交流偏壓下,頻率為20 Hz,摻合奈米銀粒子的向列型液晶胞,其臨界電壓有下降的現象;當摻合奈米銀粒子之濃度為5 wt%時,臨界電壓下降19%;當摻合奈米銀粒子之粒徑為17 nm時,臨界電壓下降21%。根據臨界電壓(Vth)公式為Vth=π ,又知Δε S與Keff S2,可推得Vth ,結果發現其臨界電壓下降,使其秩序參數降低,導致液晶胞排列亂度增加,且隨著摻合奈米銀粒子濃度增加、粒徑變大,其臨界電壓下降的比例愈大,而介電異向性、有效彈性係數也會受其影響。因此,奈米銀粒子之粒徑大小可降低扭曲向列型液晶胞之臨界電壓。
In recent years, nano-materials had the small size effect, surface effect and other properties, which displays the novel phenomenon and the unique properties, so they were applied widely including traditional industries, electro-optical and technology, electronics industries and medical. In the study, the colloidal dispersion of silver (Ag) nano-particles protected with nematic liquid crystal (NLC) molecules, 5CB (4''-n-pentyl-4-cyanobiphenyl), was synthesized by ultraviolet irradiation (UV, wavelengths of 250~450nm) of an ethanol solution of silver perchlorate (AgClO4) in the recycle system. By changing the exposure intensity, the concentration of silver perchlorate and UV illumination time that can control the particle size of silver nano-particles. Twist nematic liquid crystal cells (TN-LC cells) doped with silver nano-particles which were protected with the same NLC molecules of 5CB. Then, we used the UV-Vis, FTIR, XRD, ICP-AES and TEM for instrumental analysis in subsequent. As the concentration of silver perchlorate was 0.05M, the molar ratio of 5CB to AgClO4 was 1, the exposure intensity of ultraviolet irradiation was increased to 50mW/cm2, and the time of ultraviolet irradiation was 3 hours, the yield and the mean size of as-synthesized silver nano-particles were 43% and 17nm, respectively. As the concentration of silver perchlorate was 0.01M, the exposure intensity of ultraviolet irradiation was 25mW/cm2, the time of ultraviolet irradiation was 3 hours, and the molar ration of 5CB to AgClO4 was increased to 5, the mean size of as-synthesized silver nano-particles was decreased to 7nm. As the concentration of silver perchlorate was 0.05M, the molar ration of 5CB to AgClO4 was 1, and the exposure intensity of ultraviolet irradiation was increased was 50mW/cm2, when the UV illumination time increases to 21 hours, the concentration of silver nano-particles was not increased by UV-Vis spectrum measurement and the yield of as-synthesized silver nano-particles was 76%. For the electro-optic properties, we discussed the effect of the silver nano-particles doping TN-LC cells. The experimental results expressed that the TN-LC cells containing silver nano-particles have lower threshold voltages under external dc voltage and the frequency was 20Hz. As the concentration of the TN-LC cells doped with silver nano-particles was 5wt%, the decreasing ratio of threshold voltages was 19%. As the mean size of the TN-LC cells doped with silver nano-particles was 17nm, the decreasing ratio of threshold voltages was 21%. According to the formula, Vth=π was calculated from the well known proportionalities Keff S2, which was an approximate relation in TN-cells and Δε S, then we had Vth , as a result, the origin of the reduction of the threshold voltage was attributed to the reduction of the order parameters by doping silver nano-particles, the decrease of threshold voltage of the cell results in the lower entropy of liquid crystal cell. The dielectric anisotropy and the effective elastic constant will also be dependent of the increase of silver nano-particle concentration and size. Therefore, the threshold voltage of the twisted TN-LC cells can be reduced by the control of particle size of silver nano-particle.
URI: http://hdl.handle.net/11455/3820
其他識別: U0005-1808201015153700
文章連結: http://www.airitilibrary.com/Publication/alDetailedMesh1?DocID=U0005-1808201015153700
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