Neutron-Reflectometry-Based In Situ Structural Analysis of an Additive Aligning Agent for the Alignment of Nematic Liquid Crystals on Solid Substrates
Neutron-Reflectometry-Based In Situ Structural Analysis of an Additive Aligning Agent for the Alignment of Nematic Liquid Crystals on Solid Substrates
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基于中子反射法的用于固体基底上向列液晶取向的添加剂取向剂的原位结构分析
DOI：
10.1039/d1sm01355f
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发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Hideki Seto
中科院分区：
文献类型：
--
作者：
Fumiya Nemoto;Norifumi L. Yamada;Masahiro Hino;Hiroyuki Aoki;Hideki Seto
表面取向剂，例如两亲表面活性剂，广泛用于控制液晶显示器（LCD）中向列液晶（NLC）的初始取向。通常，在引入 NLC 之前，首先将这些试剂涂覆在基材上。当与 NLC 混合时，长烷基链两亲剂添加剂可以控制 NLC 排列，无需预处理，因为它们可以在固体-NLC 界面自发形成吸附层。这些自组装层（SAL）在有效控制液晶显示器的初始对准方面似乎很有前景。然而，由于探针的限制，直接观察与 NLC 接触的吸附层结构具有挑战性。此外，之前没有报道过在固体-NLC 界面处从 NLC 吸附的两亲物的面密度和排列。在此，使用原位中子反射计（NR）在硅-NLC界面上研究了表面取向剂正十六烷基三甲基溴化铵（d-CTAB）的结构，结果表明CTAB自组装为单层，其取向取决于两亲物浓度。在低两亲物浓度下，SAL 和 NLC 的排列与基材平行。随着两亲物浓度的增加，吉布斯单分子层框架内附着在基材上的两亲物数量增加，两亲物和 NLC 的排列变得垂直于基材。这里使用的实验设置与更自然的系统相当，例如在 LCD 中的 NLC 对齐中发现的系统。
Surface aligning agents, such as amphiphilic surfactants, are widely used to control the initial alignment of nematic liquid crystals (NLCs) in liquid crystal displays (LCDs). Generally, these agents are first coated on a substrate prior to NLC introduction. When mixed with NLCs, long alkyl chain amphiphilic agent additives may control the NLC alignment without requiring pretreatment because they may spontaneously form an adsorbed layer at the solid–NLC interface. These self-assembled layers (SALs) appear promising in the effective control of the initial alignment of LCDs. However, direct observation of the adsorbed layer structure in contact with the NLCs is challenging due to probe limitations. Furthermore, the areal densities and alignments of the amphiphiles adsorbed from NLCs at the solid–NLC interface are not previously reported. Herein, the structure of the surface aligning agent n-hexadecyltrimethylammonium-d42 bromide (d-CTAB) was investigated at the silicon–NLC interface using in situ neutron reflectometry (NR), which indicated that the CTAB self-assembled as a monolayer, with its alignment dependent on the amphiphile concentration. At low amphiphile concentrations, the alignment of the SAL and NLCs was parallel to the substrate. With increasing amphiphile concentration, the number of amphiphiles attached to the substrate increased within the framework of the Gibbs monolayer, with the alignment of the amphiphiles and NLCs becoming perpendicular to the substrate. The experimental setup used here is comparable to those of more natural systems, such as those found in the alignment of NLCs in LCDs.