多面體矽氧烷奈米粒子誘導液晶分子垂直配向液晶盒之電光特性與應用

Application and Electro-Optical Properties of Polyhedral Oligomeric Silsesquioxanes Nanoparticle Induced Vertical Alignment in Liquid Crystal Displays

鄧汶瑜(Wen-Yu Teng)

指導教授 ： 金惟國

國立清華大學/工學院/化學工程學系/博士(2009年)

摘要

本研究目的在添加多面體矽氧烷(Polyhedral Oligomeric Silsesquioxanes, POSS)奈米粒子於負型液晶中，探討其對液晶顯示膜電光性質的影響。實驗發現加入POSS奈米粒子，可促使液晶產生自發性排列的特性，在不需使用任何配向膜的狀態下，即可形成垂直配向(Vertical alignment)液晶模式，其特性跟傳統垂直配向液晶模式相似。
由測試樣品的電光特性了解此配向法的配向效果應屬於弱錨定能範圍，但與傳統採用配向膜之顯示器相比，其反應時間較慢為其缺點，但因具有常溫下即可製備具垂直配向顯示器的優點，仍具有應用發展潛力。
我們應用光學設計之方法，將具有雙折射特性的聚對苯二甲酸乙二酯(Polyethylene terephthalate, PET)及非結晶型之聚碳酸酯(Polycarbonate, PC)做為基板，組立成軟性液晶顯示面板，探討在偏光模式下的電光性質。採用球型間隙子時，在軟性面板彎曲狀態，會因球型間隙子滑動產生液晶盒厚度層不均勻。使用光蝕刻法製備十字型微結構間隙子之設計，可保持彎曲狀態時，液晶盒厚度層的均勻性。
配向機制與表面錨定能的研究中，不同POSS之錨定能計算，是依據有效液晶盒厚度(Effective cell gap method)之理論計算法。由接觸角與表面能之測定、霍式紅外光譜儀與原子力顯微鏡分析，來了解POSS誘導液晶垂直配向之作用機制。
應用POSS奈米粒子與液晶間的交互作用產生的垂直配向能力，製備添加染料型主-客型液晶顯示器(Guest-host liquid crystal display, GH-LCD)。此液晶測試盒不需使用偏光片，在無施加電壓時具高透光性，在電場作用下，呈現暗態的顯示功能。此種奈米粒子誘導液晶分子垂直配向(Nanoparticles induced vertical alignment, NIVA)之方法除可取代傳統有機配向層外，尚具有常溫下製備之特性，非常適合於一般低階軟性液晶顯示器的開發應用。

關鍵字

奈米粒子 ； 液晶顯示器 ； 多面體矽氧烷 ； 垂直配向

並列摘要

The objectives of this research are the preparation and characterization of negative dielectric anisotropic liquid crystal (LC)/ polyhedral oligomeric silsesquioxanes (POSS) mixture that works as a substitute to the alignment layer for flexible displays. There are four parts in this dissertation.
The first part of this dissertation investigated the nanoparticles in the LC cell, which can exhibit the properties of vertical alignment without using alignment layers. The electro-optical properties of this nanoparticles-induced vertical alignment in the LC cell are very similar to the conventional homeotropic LC cell by using alignment layers. But it drives the manufacturing technology of flexible LC toward low temperature process.
The second part of this dissertation compared electro-optical properties of a flexible photo-spacer LC cell using amorphous PC substrates and a flexible bead-spacer LC cell using crystalline biaxially oriented PET substrates. Both types of flexible devices adopted the NIVA effect to align the LC cell without using alignment layers. Comparing to bead-spacer LCD, the photo-spacer LCD showed higher mechanical stability against external bending and a more reliable fabrication process.
The main objective of the third part of this dissertation is to examine the alignment ability of POSS films. The polar anchoring energy of a negative nematic liquid crystal (MLC-6882) aligned on POSS films were measured and calculated from the effective cell gap method. The alignment mechanism was inferred by contact angle, FTIR, and AFM studies. The absoption of the POSS particles on the ITO surface together with the interaction between LC molecule and POSS particles may be the major driving force to vertically align the LC and realize this alignment layer free technology.
The final part of this dissertation used NIVA method to fabricate a guest-host liquid crystal display (GH-LCD). This GH-LCD exhibited a high reflectance of ~59% in the voltage-off state and a low threshold voltage of ~2.0V. Finally, the same technology was used to fabricate a flexible timepiece.

並列關鍵字

nanoparticle ； liquid crystal display ； Polyhedral Oligomeric Silsesquioxanes ； vertical alignment

參考文獻

[12] 黃柏喻，大面積量測奈米粒子誘使液晶垂直配向之軟性顯示器，國立清華大學碩士論文(2008).

[14] 陳振昌，軟性顯示器之光電特性量測，國立清華大學碩士論文(2006).

[1] G. P. Crawford, Flexible Flat Panel Displays, John Wiley & Sons Press, England (2005).

[1] F. Reinitzer, Monatsh. Chem. 9, 421(1888).

[4] P. G. de Gennes and J. Prost, “The Physics of Liquid Crystals”, 2nd ed., Clarendon Press, Oxford(1993).