Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device.
Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device.
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DOI：
10.1021/la5034614
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发表时间：
2015-04-14
期刊：
影响因子：
--
通讯作者：
Safinya CR
中科院分区：
文献类型：
--
作者：
Silva BF;Zepeda-Rosales M;Venkateswaran N;Fletcher BJ;Carter LG;Matsui T;Weiss TM;Han J;Li Y;Olsson U;Safinya CR
在这项工作中，我们研究了微流体装置中流动和限制下热致向列液晶取向场中流动和边界条件影响之间的相互作用。使用同步加速器小角度 X 射线散射 (SAXS) 进行了两种类型的实验。第一种方法中，向列液晶以不同的流速流过方形通道横截面，同时使用 2D 检测器测量投影到速度/速度梯度平面上的向列指向矢方向。在中高流速下，向列导向器主要沿流动方向排列，但在速度梯度方向上有约±11°的小倾斜角。指向矢倾斜角在大部分通道宽度上是恒定的，但在穿过通道中心时会改变符号，这与 Ericksen-Leslie-Parodi (ELP) 理论一致。在低流速下，边界条件开始占主导地位，并且观察到类似于逃逸径向导向器配置的流动剖面，其中可以看到导向器从通道边缘（具有垂直排列）到通道中心更平滑地变化。在第二个实验中，采用流体动力聚焦将向列相限制在夹在两层 Triton X-100 水溶液之间的液体层中。平均向列导向器取向在一定程度上从流动方向向液体边界移动，尽管目前尚不清楚是否一个倾斜角在大部分向列片中占主导地位（在边界附近突然跳跃），或者倾斜角是否在两个极值（∼90°和0°）之间平滑变化。这里介绍的技术可用于执行高通量测量，以评估不同表面活性剂对向列相取向的影响，并可能导致边界润滑和澄清液晶显示器中缺陷结构的性质等领域的进一步改进。
In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ∼±11° in the velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen–Leslie–Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (∼90 and 0°). The technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays.
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DOI：
10.1051/jp2:1993211
发表时间：
1993-09-01
期刊：
JOURNAL DE PHYSIQUE II
影响因子：
--
作者：
DIAT, O;ROUX, D;NALLET, F
通讯作者：
NALLET, F
影响因子：
4.6
作者：
Cubaud, Thomas;Mason, Thomas G.
通讯作者：
Mason, Thomas G.
影响因子：
16.6
作者：
Hakansson, Karl M. O.;Fall, Andreas B.;Lundell, Fredrik;Yu, Shun;Krywka, Christina;Roth, Stephan V.;Santoro, Gonzalo;Kvick, Mathias;Wittberg, Lisa Prahl;Wagberg, Lars;Soderberg, L. Daniel
通讯作者：
Soderberg, L. Daniel
影响因子：
2.4
作者：
Hamley, I. W.;Castelletto, V.;Parras, P.
通讯作者：
Parras, P.
影响因子：
6.1
作者：
Barrett, R;Faucon, M;Salmon, JB
通讯作者：
Salmon, JB