Name: orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets
Uploaded: 2017-05-15T13:00:00.000+00:00
Duration: 6 min 26 s
Description: Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

这项工作得到JSS KAKENHI授权号16H06037的支持。衷心感谢北海道大学佐佐木博士对HR-DSC的技术支持。

1.将全氟聚合物的液晶对准层制备到玻璃基板上<ol><li> 制备全氟聚合物溶液 <ol><li>通过以1:2的比例将全氟聚合物溶液（9重量％聚合物）溶解在市售溶剂中来制备1mL全氟聚合物溶液;这样可以确保0.5-1μm厚的均匀的薄膜被旋涂。 注意:请参阅材料清单，了解所用溶液和溶剂。 </li></ol></li><li> 将全氟聚合物涂覆在干净的玻璃基板上 <ol><li>通过在38或42kHz的碱性洗涤剂中超声波处理玻璃基板（典型尺寸:1cm×1cm）。反复用蒸馏水冲洗。一般冲洗10次以上，每次超声处理5分钟。 </li><li>将基材用于UV-O 3清洁剂10分钟。 </li><li>将20μL从步骤1.1的溶液滴入清洁的玻璃基质上工商业污水附加费。立即将溶液以3500rpm和室温旋涂70秒。将膜在80℃下烘烤60分钟以除去溶剂，并在200℃下烘烤60分钟以固化。 </li></ol></li></ol> LC细胞的制备<ol><li>使用光固化树脂和波长为365nm（1.1W / cm 2 ）的LED灯将两片涂有薄膜的玻璃基板胶合。通过使用微米级玻璃颗粒或聚萘二甲酸乙二醇酯膜，将两个基板之间的间隙厚度调整在2-100μm的范围内。 </li><li>在高于各向同性液体（I）的温度下，使用刮刀在毛细管力下将LC物质4&#39;-丁基-4-庚基 - 双环己基-4-甲腈（CCN47;0.2-10μL） 9引入制备的LC细胞中， （N）相变温度。 注意:CCN47具有负介电各向异性，相序为Cry 298.6 K SmA 301.3 KN 331.3 KI，其中Cry和SmA代表晶体和近晶相。不要在N相或SmA相中引入CCN47，因为可以促进流动引导的对准。 </li></ol>样品表征<ol><li> 通过偏光光学显微镜（POM）进行纹理观察10 <ol><li>观察POM下的LC细胞与4-100X物镜结合热阶段，以±0.1-K的精度控制样品温度。将纹理记录在超过5帧，以开尔文为间隔。在291-343K范围内冷却和加热时，请依次使用数码彩色照相机。 </li></ol></li><li> 介电光谱（DS） 11 <ol><li>制备具有ITO电极的LC电池，其可以具有正方形或圆形并且可以在两种基板上商业购买。将引线焊接到每个基板。 注意:请参阅所用基材的材料清单。 </li><li>使用商用阻抗/增益相位分析仪测量LC单元的电容或介电常数，与POM一样。确保在每次测量之前均衡样品的状态。通过每5分钟手动测量LC电池的电容来测量电容的时间依赖性或LC单元的介电常数。 </li><li>仅当LC单元的电容或介电常数变得非时间依赖时才启动DS测量。 </li></ol></li><li> 高分辨率差示扫描量热法（HR-DSC） 12 <ol><li>将LC细胞置于自制的HR-DSC中，与POM（ 不使用DSC平底锅）完全相同。参考参考12设计和构建HR-DSC并学习如何使用它。以0.05-0.10 K / min的扫描速率进行测量，以提高最低温度解析度呃。 </li></ol></li><li> 放射X射线衍射（GI-XRD） 13 <ol><li>将LC单元（用于POM或DSC）或具有2至5μLCCN47液滴的样品放置在GI-XRD样品台上的涂覆基材上，该样品台应配备温度控制器。 </li><li>在冷却和加热下，在291-343 K范围内的所需温度下将样品平衡超过10分钟。 </li><li>在样品上使用入射的X射线束，以0.05-0.10°的微小入射角提取分子取向和排列/结构的表面信息。摆动X射线束的入射角，找到衍射强度最强的最佳入射角。以最佳入射角度进行测量。 注意:请注意，GI-XRD可以探测纳米尺度的界面特性，从而最大化来自薄层的信号同时尽量减少大量信号。注意，除了GI-XRD之外，正常的XRD几何不是表面敏感的方法，因为X射线辐射束具有大的材料穿透深度。 </li></ol></li></ol>

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作者没有什么可以披露的。

使用5-μmLC单元（ 图1a和b ）拍摄的10x POM图像清楚地表明，当以一级方式温度变化时，本体LC分子的取向状态在P和V取向之间转变。这是由领域成核和生长过程标记的，其新方向与初始取向不同，为90°。冷却和加热时的转变温度分别为321.5K和325.3K。由于CCN47的双折射为〜0.02 9 ，当LC单元的厚度在5-20μm的范围内时，Schlieren纹理的可视性是好的。如果厚度小于该范围，则Schlieren纹理的透射率变得较低，这导致较差的可见度。另一方面，如果厚度大于该范围，则光的干涉和散射导致POM图像中的像差，降低vi灵敏度甚至有效的光学分辨率。 为了定量研究LC导向器相对于正常表面（ 即极角）的倾斜角，在1kHz（远离导电频率范围）的固定频率下的DS测量同时进行POM作为温度的函数（ 图1c ）。由于使用的LC的介电各向异性通过使用具有P和V取向层的电池预先测量为温度的函数，所以在取向转变时介电常数（ℇ）的变化可以转化为极性的变化散装角度的LC。在图1c中 ，冷却和加热两者之间的曲线明确表明，从P（V）到V（P）的取向转变突然发生，迹线跳跃很大。从ℇ的大不连续性可以看出，方向转型具有一级性质，与POM的观察一致。即使DS测量足够强大来估计各向异性材料的极角，它缺乏深度分辨率，也不能给出面内方位角方向上的任何信息。 在图2a中 ，25μmLC电池中的HR-DSC迹线确认了热流的逐步变化，在约318K（在〜328K加热）下冷却时在取向转变处交叉，此时体取向状态从P变为V状态。此外，在〜332K的体积IN相变和〜303K的体积N-SmA相变时的热异常。高于0.05-0.10K / min的扫描速率将导致较差的温度分辨能力和噪声在热流中，会使目标样品脱离平衡状态。方向转换时热流的准逐步变化不伴随可测量的潜热，其代表存储在分子之间的键中的势能。这不同于涉及大量潜热的正常LC和晶体相变。这意味着每单位体积的热流量d Q / d t d V与比热容C p （ 即 d Q / d t d V〜C p ）直接相关。这种结果使得有可能确定完成从P到V的取向转变的体分子（ X ）的分数。这反过来又提供了对通过Kolmogorov-Johnson-Johnson的取向转变的成核和生长过程的理解， Mehl-Avrami，（KJMA或Avrami）分析16,17,18。 图2b给出了基于方程的Avrami拟合<img alt="方程" src ="/ files / ftp_upload / 55729 / 55729eq1.jpg"/&gt;，其中X ， K ， t和n分别是新域的体积分数，温度相关的Avrami系数，时间和Avrami指数）。 n被证实是〜2.6，表明异质成核和随后的2D生长界面润湿过程。该结果与通常的大容量NLC中的各向同性向列转变（n≈3.6）的Avrami指数形成鲜明对比（参见参考文献8中的支持信息）。请注意，由于我们的HR-DSC具有出色的温度分辨能力和良好的信噪比，因此目前的KJMA分析是可行的。这不能通过传统的DSC仪器来实现。由于这种技术对热流的小变化敏感（ 例如，即使是纳米丝的成核/生长过程也是可检测的），它具有测量小an在从有机材料到金属的任何材料的结构和阶段。此外，我们强调，这种技术在样本几何中的限制较少（ 例如，常规DSC仪器无法测量的LC单元）。 具有全氟聚合物表面的样品的GI-XRD图（ 图3a ）确认SAD和WAD峰，在I相的332K以外的温度下具有方向性。代表沿着LC分子的长轴的顺序的前者平行于表面延伸。表示沿着LC分子的短轴的顺序的后者位于垂直于前者的位置。 SAD峰强度比WAD峰强，SAD峰的FWHM也比WAD峰更窄。由于衍射峰的FWHM是痣之间位置相关强度程度的主要测量证明，存在沿着LC分子的长轴而不是沿着短分子的较长的位置相关性。这表明在表面附近存在上述SSWS。 如图3b所示 ，几个分子长度的近晶相关长度为纳米级。这种在纳米尺度和介观尺度上的局限于界面区域的信息只能通过表面敏感的XRD几何提取，例如在GI-XRD中，但不能通过传统的透射和反射几何来提取。此外，如果GI-XRD的入射角太大（〜&gt; 0.1°），则全反射条件将被破坏，并且不能再探测到表面特异性结构。

近年来，人们越来越关心学习如何响应于外部刺激的表面分子的动态分子特征和结构可能影响LC状态下材料的体取向。一个例子是使用LC生物传感器作为LC1,2的新应用。为了量化检测到多少目标生物物种，重要的是要知道接触粘附目标分子的界面LC如何变化和演化，同时也检测它们如何将其性质转移到体内。 使用模型来追求这些答案，我们从具有表面分子取向和短程排序的系统开始，热力学变化。这些系统允许我们以系统的方式将表面取向和排序的变化与所得到的体积方向相关联。最近，我们发现了几个显示o的LC系统自发体积分子取向随温度变化。原则上，定向转换可以分为准二阶3,4或准一阶转换5,6,7,8。前者伴随着温度变化时的连续大分子重新取向，而后者则表现出不连续的。在本文中，我们描述了P和V定向状态之间的准一阶方向的取向转变。它通过改变温度在单向向（N）相中进行。详细情况将在代表结果和讨论中提供。 由于体积的取向变化应受表面分子取向的变化和短期的限制很明显的是，该系统可以潜在地了解表面分子取向和短程排序的热力学变化如何影响体取向。在本文中，为了理解上述问题，我们使用四种补充方法（ 即 POM，DS，HR-DSC和GI-XRD）解决了三个问题:（1）定向过渡是什么样的？ （2）取向转变是否可热？ （3）为什么和如何发生方向转变？

<table><tbody><tr><td>CYTOP</td><td>Asahi Glass Co. Ltd.</td><td>CTX-809A</td><td></td></tr><tr><td>Solvent for CYTOP</td><td>Asahi Glass Co. Ltd.</td><td>CT-180 Sol.</td><td></td></tr><tr><td>Alkaline detergent</td><td>Merck KGaA</td><td>Extran MA01</td><td></td></tr><tr><td>NOA61</td><td>Norland Products, Inc.</td><td>#37-322</td><td>Purchasable from Edmund Optics</td></tr><tr><td>AL1254</td><td>JSR Corporation</td><td></td><td>Planar alignment material in self-made cells</td></tr><tr><td>4&amp;rsquo;-butyl-4-heptyl-bicyclohexyl-4-carbonitrile</td><td>Nematel GmbH &amp;amp; Co. KG</td><td></td><td>Custom-made</td></tr><tr><td>UV-O&lt;sub&gt;3&lt;/sub&gt; cleaner</td><td>Technovision Inc.</td><td>UV-208</td><td></td></tr><tr><td>Hot-stage system</td><td>Mettler Toledo</td><td>HS82</td><td></td></tr><tr><td>High-Definition Color Camera Head</td><td>Nikon</td><td>DS-Fi1</td><td></td></tr><tr><td>Impedance/gain-phase analyzer</td><td>Solartron Analytical</td><td>1260</td><td></td></tr><tr><td>Indium Tin Oxide (ITO)-coated substrate</td><td>GEOMATEC Co. Ltd.</td><td></td><td>Custom-made</td></tr></tbody></table>

orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

在液晶（LC）物理化学中，表面附近的分子在控制体取向方面起着很大的作用。到目前为止，主要是为了在LC显示器中实现期望的分子取向状态，已经深入研究了LC的"静态"表面性质，即所谓的表面锚定。根据经验，一旦LC的初始取向通过特定的表面处理（例如用特定取向层的摩擦或处理）"锁定"，则几乎不随温度变化。在这里，我们提出一个体现温度变化的方向转变的系统，与共识相冲突。在转换过程中，体积LC分子经历取向旋转，在高温下的平面（P）取向与低温下的垂直（V）取向之间呈90°，以一阶过渡方式。我们通过偏振光学显微镜跟踪热力学表面锚固行为（POM），介电光谱（DS），高分辨率差示扫描量热法（HR-DSC）和掠入射X射线衍射（GI-XRD），并达到合理的物理解释:转变由表面生长引发润湿片材，其在本体上局部抵抗P取向局部施加V取向。这种景观将提供一个通用的链接，说明在许多液相色谱系统中平衡体取向受到表面定向取向的影响。在我们的表征中，通过提供关于LC分子的取向的空间分布的信息，POM和DS是有利的。 HR-DSC提供关于转换的精确热力学信息的信息，由于分辨率有限，传统DSC仪器无法解决。 GI-XRD提供关于表面特异性分子取向和短程排序的信息。本文的目的是提出一种用于准备展示transi的样品的方案并演示如何通过上述方法分析体积和表面上的热力学结构变化。

在温度变化期间收集POM图像，DS数据，HR-DSC数据和GI-XRD图案，特别是在冷却和加热两者的取向过渡附近。 图1表示在冷却（加热）期间从P（V）到V（P）取向状态的取向转变的POM观察期间由POM和DS测量形成的纹理的演变。显示了基于POM观察的取向转换过程中的重新定向过程（ 图1a ）。在冷却时，体积中的P取向正好低于IN转变温度，由二维（大多数）和四刷Schlieren纹理的外观来区分。值得注意的是，两刷Schlieren（具有s =±1/2的拓扑强度的旋转）是resu具有线缺陷的光结构，其拓扑上不允许在表面导向器14中预倾斜。另一方面，四刷Schlieren（具有s =±1的拓扑强度的旋转）具有点奇点，其可以存在于表面上或大量存在。与两刷Schlieren不同，根据对称论证允许表面导向器的预倾斜。通过将温度降低至321.5K，暗域（V取向）主要从±1旋错点的奇异点成核并随时间扩散。通过将样品退火数分钟或通过进一步冷却，整个视野变得完全变暗，这表明在体内从P向V方向的转变完成。在加热时，体积中从V到P取向的反向取向转变与冷却的重要不同:在5K附近的滞后，建议发现了一个强大的一阶转型。请注意，LC-LC转换的典型滞后范围（ 例如， IN和N - 近晶相变）小于1 K. 图2显示了通过HR-DSC测量的表示通过样品的热流的HR-DSC数据作为温度的函数（ 图2a ）和时间（ 图2b的插图）。 图2b插图中的数据用于分析取向转变后的Avrami指数（ 图2b ）。 图3显示了在各种温度下的两个样品几何中的GI-XRD图案:液滴几何（ 图3a ，顶部）和原位 LC单元几何形状（ 图3a &lt;/ strong&gt;，底部）。两者都表现出准SmA润湿片的短程排序，其中在表面附近形成层结构（以下简称为SSWS）。由GI-XRD峰的半峰全宽（FWHM）计算SSWS的大小（ 图3b ）。有两个关键的观察证实，SSWS应该是表面特定的结构:（1）如XRD所证实的，在CCN47的大部分中没有SmA排序（这里未示出）。 （2）在常规的P取向层材料上证实了在SAD（比全氟聚合物表面更弱和更宽的）和WAD的各向同性衍射图，证实了全氟聚合物和CCN47之间的特殊的分子相互作用。由于关于分子相互作用的争论超出了本讨论范围，它们将在未来的其他地方报告。令人惊讶的是，即使在P定向状态的温度范围内（见GI在328和322 K处的-XRD图），SSWS持续存在，表明表面取向条件受挫。表面的一些部分处于SSWS的斗篷下，呈现体积LC分子的V对准能力，而其余部分暴露出P对准能力。如果SSWS的尺寸或覆盖范围随着温度而变化，我们预期体积LC取向状态可能会发生变化，因为V对准能力与P对准能力的比值会相应变化。为了证实这种可能性，从SAD峰的FWHM计算SSWS相关长度（ 即，与表面垂直的方向上的SmA短程顺序的平均持续长度）的温度依赖性。 图3b证实了预期的趋势，显示在N相上的SSWS相关长度的增加以及潜在的滞后。滞后是指在SSWS形成之后e表面，在热力学上稳定，即使在高温下也是耐用的。关键特征是滞后范围与POM和DS确认的滞后范围一致（ 图1 ）。这表明定向转型是由SSWS的增长引发的。 <img alt="图1" class="xfigimg" src="/files/ftp_upload/55729/55729fig1.jpg" /> 图1:在冷却和加热时从P向V取向状态的取向转变的演变。 （ a ）冷却（蓝色向下箭头）和（ b ）加热（红色向上箭头）的纹理变化。 （ a ）顶部:P方向出现在IN转换下方。 （ a ）中间:在T C （ 即冷却时的取向转变温度），V取向从点defec出现t主要是四刷Schlieren纹理（红色虚线圆）。 （ a ）底部:具有V方向的区域扩展并覆盖整个视野，由内窥镜图像的插图补充。请注意，十字形圆锥视野图像在低温下几乎没有变化。 （ b ）底部:在T H （ 即，加热时的取向转变温度），暗和明亮的施利伦纹理使其从V取向域出现，表明薄层和厚层与P取向共存。 （ b ）中间:暗域转换为明亮的域。 （ b ）顶部:整个领域的导演是P方向，展现出一个薄的四刷Schlieren纹理。 （ c ）在两个冷却（空心圆圈）和加热（十字标记）之间测量的介电常数的温度依赖性。蓝线是实验在垂直LC单元中测量的CCN47的介电常数的数据。这个数字经过参考文献15的许可修改和修改。版权所有2012，美国物理学会。 <a href="http://ecsource.jove.com/files/ftp_upload/55729/55729fig1large.jpg" target="_blank">请点击此处查看此图的较大版本。</a> <img alt="图2" class="xfigimg" src="/files/ftp_upload/55729/55729fig2.jpg" /> 图2:使用HR-DSC的取向转变的热追踪。 （ a ）冷却和加热后涂覆全氟聚合物的电池中的HR-DSC图。在冷却之后，用常规的平面取向层材料AL1254涂覆的LC单元的结果也显示为对照测量。三个HR-DSC图表的基线正确转移。双箭头比例尺对应于1 mW / g。虚线被强调V方向的热流量比在全氟聚合物表面的电池中的P取向和I相中的热流小。 （ b ）用于区域的成核生长过程的Avrami拟合，其中V取向从冷却后具有P取向的区域产生。热流随时间的变化在插图中显示，用于Avrami拟合。这个数字经过参考文献7,8的许可修改和修改。版权所有2012，美国物理学会，版权所有2016，美国化学学会。 <a href="http://ecsource.jove.com/files/ftp_upload/55729/55729fig2large.jpg" target="_blank">请点击此处查看此图的较大版本。</a> <img alt="图3" class="xfigimg" src="/files/ftp_upload/55729/55729fig3.jpg" /> 图3:界面LC结构的热力学变化分析。 </（ a ）使用CCN47液滴在全氟聚合物表面上的GI-XRD图案相对于温度的变化和全氟聚合物表面上的LC单元。在具有P取向层材料AL1254的表面上的CCN47液滴的GI-XRD图案被示出为参考。 （ b ）冷却和加热时的近晶相关长度ξ∥的温度依赖性，由GI-XRD的小角度衍射图的半峰全宽计算。这个数字经过参考文献7,8的许可修改和修改。版权所有2012，美国物理学会;版权所有2016，美国化学学会。 <a href="http://ecsource.jove.com/files/ftp_upload/55729/55729fig3large.jpg" target="_blank">请点击此处查看此图的较大版本。</a>

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

在这里，我们提出一种协议来触发液晶响应于温度的取向转变。描述了制备样品以观察转变和详细过渡演化的方法。

由界面润湿片的热力学生长触发的液晶中的定向转变

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

orientational-transition-liquid-crystal-triggered-thermodynamic

Nanyang Technological University

Research

JoVE Journal

Engineering

7.1K 次观看.  RIKEN Center for Emergent Matter Science (CEMS). 在这里，我们提出一种协议来触发液晶响应于温度的取向转变。描述了制备样品以观察转变和详细过渡演化的方法。 

视频: Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

干式氧化及真空退火处理调整的润湿性能的碳纳米管阵列

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

科研

工程学

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

重组的影响在液体电离室表征用于一个电波加速器的剂量学

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

相图表征使用磁珠用作液体载体

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

合成与盘状磷酸盐锆剥落获取胶体液晶

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

化学

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

光诱导的宏观振荡运动液晶网络的制备

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

观测 Photoresponsive 液晶结构动力学的新方法

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

液晶弹性体致动器的微流控制备

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

液晶中磁调谐铁电极化的测量

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Preparation of Monodomain Liquid Crystal Elastomers and Liquid Crystal Elastomer Nanocomposites

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and as soft robots. Here, we demonstrate the preparation of shape-responsive liquid crystal elastomers (LCEs) and LCE nanocomposites along with characterization of their shape-responsiveness, mechanical properties, and microstructure. Two types of LCEs &#8212; polysiloxane-based and epoxy-based &#8212; are synthesized, aligned, and characterized. Polysiloxane-based LCEs are prepared through two crosslinking steps, the second under an applied load, resulting in monodomain LCEs. Polysiloxane LCE nanocomposites are prepared through the addition of conductive carbon black nanoparticles, both throughout the bulk of the LCE and to the LCE surface. Epoxy-based LCEs are prepared through a reversible esterification reaction. Epoxy-based LCEs are aligned through the application of a uniaxial load at elevated (160 &#176;C) temperatures. Aligned LCEs and LCE nanocomposites are characterized with respect to reversible strain, mechanical stiffness, and liquid crystal ordering using a combination of imaging, two-dimensional X-ray diffraction measurements, differential scanning calorimetry, and dynamic mechanical analysis. LCEs and LCE nanocomposites can be stimulated with heat and/or electrical potential to controllably generate strains in cell culture media, and we demonstrate the application of LCEs as shape-responsive substrates for cell culture using a custom-made apparatus.

We demonstrate the preparation of siloxane-based and epoxy-based liquid crystal elastomers (LCEs) and LCE nanocomposites. The LCEs are characterized with respect to reversible strain, liquid crystal ordering, and stiffness. As a potential application, we demonstrate their use as shape-responsive substrates in a custom device for active cell culture.

单域液晶的弹性体和液晶橡胶纳米复合材料的制备

LCEs are shape-responsive materials with fully reversible shape change and potential applications in medicine, tissue engineering, artificial muscles, and ...

生物工程

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such as on-demand switchable adhesion technologies, actuators, molecular clutches, and nano-/microscopic mass transporters. Recently it was found that through a special solid-liquid transition, rheological properties can exhibit significant changes, thus providing suitable smart viscoelastic materials. However, designing materials with such a property is complex, and forward and backward switching times are usually long. Therefore, it is important to explore new working mechanisms to realize solid-liquid transitions, shorten the switching time, and enhance the contrast of rheological properties during switching. Here, a light-induced crystal-liquid phase transition is observed, which is characterized by means of polarizing light microscopy (POM), photorheometry, photo-differential scanning calorimetry (photo-DSC), and X-ray diffraction (XRD). The light-induced crystal-liquid phase transition presents key features such as (1) fast switching of crystal-liquid phases for both forward and backward reactions and (2) a high contrast ratio of viscoelasticity. In the characterization, POM is advantageous in offering information on the spatial distribution of LC molecule orientations, determining the type of liquid crystalline phases appearing in the material, and studying the orientation of LCs. Photorheometry allows measurement of a material&#8217;s rheological properties under light stimuli and can reveal the photorheological switching properties of materials. Photo-DSC is a technique to investigate thermodynamic information of materials in darkness and under light irradiation. Lastly, XRD allows studying of microscopic structures of materials. The goal of this article is to clearly present how to prepare and measure the discussed properties of a photorheological material.

This protocol demonstrates the preparation of a photorheological material that exhibits a solid phase, various liquid crystalline phases, and an isotropic liquid phase by increasing temperature. Presented here are methods for measuring the structure-viscoelasticity relationship of the material.

扭曲弯曲的液晶的高对比度和快速光圈开关

Smart viscoelastic materials that respond to specific stimuli are one of the most attractive classes of materials important to future technologies, such ...