这项工作得到了荷兰科学研究组织的资助 (NWO 最高平底船赠款: 10018944) 和欧洲研究理事会 (震动紧急救济委员会, 赠款 669991)。a.h.g. 承认, 欧洲联盟第七框架计划 FP7-2013 的 "人民计划" (居里夫人行动) 提供资金, 赠款 No. 607602。

注意: 总体过程详见 图 1 . 
 1. 细胞的制备 <ol> <li> 清洗玻璃板材 <ol> <li> 仔细清洁 3 cm x 3 cm 玻璃板材, 使用肥皂和热水去除污染物 ( 图 1A ). </li>
		<li> 将玻璃盘放在烧杯中, 并用乙醇 99.5% ( 图 1B ) 覆盖. </li>
		<li> 将烧杯放入超声波槽中约10分钟. </li>
		<li> 小心地用纸巾和空气吹干玻璃板. </li>
		<li> 确保没有任何溶剂、灰尘或任何类型的污染痕迹留在盘子上. 
		注 : 玻璃板材现在是干净的 , 并且应该纵用手套 . </li>
		<li> 将玻璃板放在紫外线-臭氧反应器中20分钟, 以去除任何有机残留物。在臭氧处理后, 板已准备好进行涂层步骤 ( 图 1C ). </li>
	</ol> </li> <li> 玻璃板涂层 注: 两套镀膜板准备就绪: 一组具有平面对齐层, 另一套具有垂直对准。在以后的阶段, 细胞将由一个平面玻璃板和一个垂直玻璃板 ( 图 1D ) 组成。
	<ol> <li> 空气吹玻璃板并将其放置在旋转涂布机上. </li>
		<li> 将聚酰亚胺溶液沉积到玻璃板上以覆盖整个表面 (约0.5 毫升溶液). </li>
		根据以下条件 <li> 自旋涂层对齐层: 程序 1: 5 s at 17 x g, 加速度为 11 x 克/秒;节目 2: 四十年代在 420 x g 和加速度 17 x g/s. </li>
	</ol> </li> <li> 对齐图层的固化 <ol> <li> 将镀膜玻璃板放在110和 #176 的热板上; C 为10分钟, 以去除对齐层混合物中存在的大部分溶剂 ( 图 1E ). </li>
		<li> 将玻璃板 (在涂一侧) 标记为识别垂直和平面对齐层的独特标志。小箭头通常对平面玻璃板有帮助, 因为它还指示在稍后阶段 ( 图 1F ) 中描述的摩擦方向. </li>
		<li> 一旦所有的玻璃板被涂上, 溶剂被除去, 将玻璃板放在烤箱中180和 #176; C 为 1 h 以固化聚酰亚胺层 ( 图 1G ). 
		注意: 这一步涉及极端高温;戴上手套、眼镜和适当的个人防护. </li>
		<li> 烘烤完玻璃板后, 让它们冷却到室温. 
		注意: 为了防止每个步骤之间的任何污染, 建议在玻璃板上放置一个保护箔. </li>
	</ol> </li> <li> 摩擦平面对齐层 <ol> <li> 将涂有平面对齐层的玻璃板擦出, 以便在该层中创建 (sub) 微, 从而在一个方向上引导 LC。要做到这一点, 将玻璃板与涂层的一面向下的天鹅绒布。使用两个手指的均匀和柔软的压力。小心地将玻璃板沿着天鹅绒布的表面沿直线方向拖动。提起玻璃板并重复相同的操作三次 ( 图 1H ). 
		注意: 这是至关重要的摩擦板在一个单一的方向, 只有在前进。在一个笔直的方向来回走, 将导致一个糟糕的对齐. </li>
	</ol> </li> <li> 胶合单元格 <ol> <li> 空气吹气机使用的玻璃板. </li>
		<li> 通过将 UV 固化胶水与具有明确定义的直径20和 #181 的垫片 (玻璃珠) 混合, 准备粘合剂; m. </li>
		<li> 采取一个玻璃板涂层与平面对准层和一个玻璃板涂有一个垂直对齐层。在平面玻璃的两个相邻的拐角处放置两滴胶水。然后将另外两滴胶水从两个最后的拐角处 5 mm ( 图 1I ). </li>
		<li> 将垂直玻璃板放在上面。在玻璃板边缘之间留有约4毫米的空隙, 为 LC 混合物提供足够的空间。确保涂布的两侧相互面对. </li>
		<li> 在紫外线照射下将电池放置2分钟以固化胶水. 
		警告: UV 灯是危险的;戴上手套、眼镜和适当的个人防护. </li>
	</ol> </li> </ol> 2。lc 混合物的制备和表征 <ol> <li> 组件 <ol> <li> 重97.5 毫克的 lc 二丙烯酸 1, 2.5 毫克的光稳定剂和1毫克的光在一个棕色玻璃瓶 ( 图 2 )。由于启动器的灵敏度, 防止紫外线照射到混合物尽可能最好. </li>
	</ol> </li> <li> 粉末的均匀混合 注意: 这一步是在化学罩中执行的。
	<ol> <li> 向上述组件添加3毫升的二氯甲烷 (DCM), 然后摇动直到固体完全溶解为止. </li>
		<li> 将瓶子放在30和 #176 的热板上; C 为30分钟, 并添加一个氩气以促进 DCM 的快速蒸发. 
		注: 建议将小瓶置于真空中, 以消除 DCM 的残余痕迹. </li>
	</ol> </li> <li> 在偏振光学显微镜下观察 (POM) 进行相变测定 <ol> <li> 一旦混合物完全干燥, 在两个玻璃板之间放置少量 (和 #177; 10 毫克), 并涂上平面对准层。
		注意: 为了正确地描述相位, 建议使用 unrubbed 平面玻璃板. </li>
		<li> 将幻灯片放在装有热舞台的 POM 中。将电池加热直至图像变黑 (使用交叉偏振) 表示各向同性相. </li>
		<li> 慢慢冷却热板并注意过渡温度。对于上述混合物, 各向同性到向列向的过渡是在103和 #176; c 和向列晶过渡发生在86和 #176; c ( 图 3A ). </li>
	</ol> </li> </ol> 3。胶片准备 <ol> <li> 填充单元格 ( 图 1J ) <ol> <li> 将单元格放在垂直侧向上的热板上。将温度设置为110和 #176; C (各向同性相), 以促进细胞的填充, 因为流体比向列相的粘性小. </li>
		<li> 将部分固体混合物放在单元格的边缘. </li>
		<li> 固体熔化和液体混合物流动由毛在细胞。添加更多的混合物在边缘, 直到填充单元格. </li>
	</ol> </li> <li> 冷却到向列相和聚合 ( 图 1K ) <ol> <li> 一旦单元格被填满, 慢慢冷却 (5 和 #176; c/分钟) 到90和 #176;
		<li> 当胶片处于合适的温度时, 聚合将其置于 UV 光下90和 #176; C 为 30 min. 
		警告: UV 灯是有害的, 建议在受保护的环境中进行聚合. </li>
		<li> 建议使用 post-baking 步骤来确保网络的完全聚合。将电池放在130和 #176 的热板上; C 约10分钟, 让它慢慢冷却到室温. </li>
	</ol> </li> <li> 打开单元格并剪切样本 <ol> <li> 以开启单元格, 将刀片放在一个边缘和推动它在两个玻璃板。单元格立即打开 ( 图 1L ). </li>
		<li> 剥离胶片, 用刀片式服务器提起一个小角。如果需要, 可以将玻璃板放在热水中, 以方便胶片的去除 ( 图 1M ). </li>
		<li> 将胶片从水中取出并轻轻剥离. </li>
		<li> 沿分子控制器 (平面侧的摩擦方向) 剪切条纹的薄膜具有以下尺寸: 4 mm x 2.5 厘米 ( 图 1N ). </li>
	</ol> </li> </ol> 4。自振观测 <ol> <li> 在实验室中安装 <ol> <li> 使用自动关闭镊子钳住样本, 这样, 1.7 厘米的胶片可以自由移动. </li>
		<li> 垂直地握住样品并直接将发光二极管 (LED) 光束 (400 mW/cm 2 ) 垂直于样品。通常情况下, 光线距离样品大约20厘米。光应该到达影片的顶部, 在镊子 ( 图 4 ) 下面。所得到的振荡记录了一个高速相机 (150 帧/秒) 和分析的图像处理程序. </li>
	</ol> </li> <li> 安装带有直接阳光 <ol> <li> 按上述步骤 4.1.1, 但不是使用 LED 灯, 而是用透镜将阳光聚焦在胶片上面. </li>
	</ol> </li> <li> 热效果测量 <ol> <li> 使用热摄像机 15 (40 帧/秒) 测量振荡样本中的温度变化. </li>
	</ol>
	</li>
</ol>

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作者没有利益冲突。

这里描述的结果与以前的研究15在 LC 丙烯酸酯与6碳的间隔物是可比较的。结果表明, 该方法可以应用于不同力学性能的薄膜,16。
报道了一种光热响应 LCN 的制备方法。在所描述的协议中有一些关键的步骤, 如平面对齐层的摩擦和单元的准备。实际上, 该协议的成功依赖于高质量的 LC 扇对准, 这也限制了对薄膜的应用。
以前, 许多例子的照片-执行器的基础上 LCNs, 其中包含大量的照片开关已报告11,12,13,19。这里开发的方法的主要优点是掺杂需要的有限数量观察驱动 (和 #60; 5%) 和宽广的选择掺杂可利用.15这些结果扩展了潜在应用程序的范围。此外, 该协议的威力在于, 通过改变薄膜的模量和条纹的尺寸以及光强的大小, 变化振荡频率和振幅的能力。
这种方法可以很容易地扩展, 为自动化系统制造各种 LC 材料。本文所述的协议为 soft-robotics 和自动化材料的非平衡系统的开发铺平了道路。

对可持续能源的研究是对化石能源枯竭和气候变化的反应越来越感兴趣的领域。目前正在研究将光能转化为机械工作的方法, 如光伏发电、生物质生产燃料、太阳能裂解制氧和氢气。然而, 所有这些由光驱动的过程需要多个步骤, 然后他们的能源生产可以运行机器执行工作。虽然这些方法提供了一个大的应用面板, 但它们需要生产、储存和运输中间体 (例如、电子电位、化学燃料)。因此, 能够直接将阳光转化为宏观运动的装置, 具有简化的优点。
在过去的几十年中, 许多例子的光致动器已经开发的地方, 聚合物改变形状后, 辐照1,2,3。然而, 在大多数这些例子中, 连续的驱动需要打开/关闭指示灯从一个状态切换到另一个。到目前为止, 只有有限数量的光敏材料工作 out-of-equilibrium 被描述4,5,6,7。基于液晶网络的系统 (LCNs)8,9,10,11,12,13 , 也因为它们的内部允许以受控方式 preprogramming 变形的各向异性14。最近, 据报道, 光热效应诱导的照片稳定剂合并在 LCN 可以产生振荡运动15。
本文介绍了在连续光照射下机械振荡的 LCN 薄膜的制作方法。影片的构想详细从细胞的准备到表征和 LC 混合物的聚合。还报道了 LCN 薄膜的光驱动和运动分析。LCNs 被掺杂的分子, 可以迅速消散在网络内的热量, 从而诱导各向异性热膨胀和随后的宏观变形的电影。阴影、温度变化和材料收缩/伸长之间的相互作用产生了振荡运动15。该协议中突出显示了精确的设置, 包括光源的方向和获取此效果的示例。振荡的特点是其频率和控制的性质的 LCN。根据我们的知识, 这是第一个描述的方法创建 LCN 薄膜, 可以 self-oscillate, 由一个简单的机制, 与广泛的掺杂的工作。

<table><tbody><tr><td>&lt;strong&gt;Material&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>LC diacrylate (compound &lt;strong&gt;1: Figure 2&lt;/strong&gt;)</td><td>Syncom</td><td>custom synthesis</td><td></td></tr><tr><td>photo-stabilizer</td><td>Ciba</td><td>tinuvin 328</td><td></td></tr><tr><td>photoinitiator</td><td>Ciba</td><td>Irgacure 819</td><td></td></tr><tr><td>Alignment layer planar</td><td>JSR micro</td><td>optimer Al1051</td><td></td></tr><tr><td>Alignment layer homeotropic</td><td>Nissan chemical industry</td><td>Sunever grade 5300</td><td></td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>UV-ozone photoreactor</td><td>Ultra Violet Products, PR-100</td><td>Not available</td><td></td></tr><tr><td>spin coater</td><td>Karl-SUSS</td><td>SUSS RC spin coater CT62 V098</td><td></td></tr><tr><td>UV light</td><td>Gentec</td><td>EXFO-Omnicure S2000</td><td></td></tr><tr><td>micropearl</td><td>Sekisui Chemicals</td><td>SP220-20um</td><td></td></tr><tr><td>Glue</td><td>Gentec</td><td>UVS91</td><td></td></tr><tr><td>LED 365 nm</td><td>Thorlabs</td><td>M365LP1</td><td></td></tr><tr><td>light collimator</td><td>Thorlabs</td><td>SM2F32-A</td><td></td></tr><tr><td>high speed camera</td><td>PCO.</td><td>PCO 5.5 sCMOS camera</td><td></td></tr><tr><td>thermal camera</td><td>Xenics Infrared solution</td><td>Gobi-640-GigE</td><td>used with Xeneth software</td></tr><tr><td>Differential Scanning Calorimeter</td><td>TA instruments</td><td>Q1000</td><td></td></tr><tr><td>Dynamic Mechanical Analyzer</td><td>TA instruments</td><td>Q800</td><td></td></tr><tr><td>Polarized Optical Microscope</td><td>Leica</td><td>DM6000M</td><td></td></tr></tbody></table>

preparation of liquid crystal networks for macroscopic oscillatory motion induced by light

描述了一种基于掺杂液晶网络的策略, 在连续光照条件下, 建立了塑料薄膜的机械自持振荡。掺杂的光激发可以迅速地将光线消散到热中, 再加上各向异性的热膨胀和阴影, 从而产生了自我维持的变形。所观察到的振荡受薄膜的尺寸和模量以及光的方向性和强度的影响。该系统为 soft-robotics 和自动化系统的能源转换和收割提供了应用。
这里描述的一般方法包括创建独立的液晶膜和表征机械和热效应观察。分子对准是使用对准层 (摩擦聚酰亚胺), 通常用于显示制造行业。为了获得大变形的执行器, 液晶在扇/弯曲配置中对齐和聚合,即, 与液晶的控制器 (LCs) 逐渐从平面到垂直通过薄膜厚度。辐照后, 得到的机械和热振荡的监测与高速相机。通过图像分析, 利用图像处理程序对结果进行量化。

该协议的成功是在光照射下观察薄膜的振荡运动。振荡很大, 没有误导的结果可以看到。此外, 振荡是稳定的随着时间的推移 (时间刻度) 和小疲劳观察。
在其他方面, 扇对齐的质量对于实现自我维持的驱动 (图 5A) 是非常重要的。在分子取向的梯度在整个影片的厚度导致收缩或扩展在影片的平面或垂直边在驱动16,17,18。这种不对称反应增强了宏观运动。实验的失败 (没有弯曲, 小变形或奇怪的弯曲) 可以解释由一个恶劣的 LC 对齐。首先, 电影应该是透明的。(图 5B)。 为了在一个简单的步骤中验证正确的扇对准, 在漫射的白色光源 (图 5C-E) 上方的交叉偏振上观察到附着在玻璃基底上的胶片。通过在 xy 平面中由0°到45°之间旋转偏振, 胶片的亮度会急剧变化。通过在分子控制器周围的平面上旋转胶片, 在从顶部观看影片时, 应将颜色从黑色 (在平面上) 转换为白色 (在平面上)。类似的验证步骤可以进行聚合之前, 通过观察的细胞通过一个偏光板上覆盖着一个铝箔热板块。此外, 当薄膜被切成条, 它呈现出一个自然的曲率与曲线的中心在垂直侧。这是由于在高温下聚合产生的残余应力, 在这里, 薄膜两侧的扩展有相反的符号 (图 6A)。如果对齐不成功, 应重新考虑制备聚酰亚胺层的方法。这些细胞的产生对于获得定向薄膜是至关重要的。最关键的一步是摩擦: 一个太强的压力对板将删除部分的聚酰亚胺层, 并导致一个非常糟糕的命令层的对齐。在室温下, 胶片处于玻璃状态 (图 3B)。如果薄膜是软的和/或俗气的, 这意味着聚合没有完成, 很可能是因为辐照时间太短或引发剂退化。由于溶剂的存在可能影响 lc 混合物的相行为, 因此 lc 液晶的混合物在填充前应均匀干燥。LC 混合物应在聚合前对齐。应采取措施, 以避免热聚合过程中的对中快速通过步骤, 而不是加热的样品超过130° c 长时间。在清洁点的正上方填充电池是足够的 (110 ° c)。
高速摄影机注册的机械和热振荡确认了所提出的协议的成功 (图 7;视频 1)。当胶片夹在一端时, 将1.7 厘米自由移动, 并在平面一侧以聚焦光照射, 它展朝向平坦状态 (图 6B)。铰链位于光源焦点位置 (图 4)。胶片应该平滑地移动, 垂直于夹钳而不是侧面。然后影片开始连续移动以频率的振荡 7.6 Hz ±5% 和振幅30°±10% 为维度的影片 1.7 cm x 0.4 cm x 20 µm。热动摆测量用热照相机提出同样频率 (7.4 Hz ± 5%), 以轻微的相位延迟由于影片的惯性。此频率f由胶片的尺寸和模量15控制。振荡振幅随光照强度而变化, 并且会受到设置的影响, 特别是光在样品上的聚焦点的位置。振荡机理如下: 1) 卷曲薄膜以聚焦光照射, 掺杂剂吸收光并转化为热, 薄膜在其铰链上升温, 展在 LC 对准的方向上;2) 尖端遮蔽了胶片的铰链, 从而使其温度降低, 并随之松弛;3) 铰链再在辐射之下, 温暖和影片弯曲15。这些连续步骤的重复产生了振荡。观察这一现象的关键因素是光热效应和薄膜的阴影, 受聚焦光的强度和位置的控制 (图 4)。例如, 稍微倾斜的灯会导致样品完全卷曲。此外, 太低的光强不会给大弯曲, 因为在铰链的温度是不够的, 而太高的光强度在铰链将导致过度 (图 6C, 180 °弯曲的胶片)。实验成功的另一项要求是将设置放置在受风保护的环境中, 以避免扰动。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56266/56266fig1.jpg"> 
图 1。在14步骤 (从-n) 中获得扇对齐的 LCN 的总体过程.步骤A-C: 清洗玻璃板;步骤D-G: 玻璃板的涂层创建平面或垂直对齐层;步骤H: 用天鹅绒布擦玻璃板;步骤I: 将板材粘合成单元格;步骤J: 在向列相的相位中用 LC 混合和对齐填充单元格;步骤K: 在 UV 光下进行光聚合;步骤L-N: 打开单元格并剪切胶片以获得带材。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig1large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56266/56266fig2.jpg"> 
图 2。使用的组件的化学结构.<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig2large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56266/56266fig3.jpg"> 
图 3。单体混合物和聚合物薄膜的热表征。一个) 差分扫描 calorimetry (DSC) 的混合物在聚合之前, 以确定相转变。镶嵌: POM 图片, 缩放条形图: 100 µm. B) 聚合物薄膜的动态机械热分析 (DMTA) 测量。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig3large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56266/56266fig4.jpg"> 
图 4。显示左侧指示灯的设置的图片, 以及在指示灯前面夹住镊子的振荡胶片.插图显示了弯曲的薄膜和局部光照明的示意图表示。红色区域对应于文本中提到的温暖铰链。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig4large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/56266/56266fig5.jpg"> 
图 5。A) 扇对齐的示意图表示形式。B) 图片的玻璃细胞在前面的 TU/e 标志显示的透明度和没有颜色的电影。箭头表示平面玻璃板的摩擦方向。C-E) 在交叉偏振之间拍摄的影片的图片显示扇对齐方式的特征 (图片 D: 在 xy 平面中的45°旋转,图片 E: 从 xy 平面透视出)。对齐的分子控制器由红色箭头指示。缩放栏: 1 厘米.<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig5large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/56266/56266fig6.jpg"> 
图 6。a) 影片的图片, 用镊子显示一个自然的曲率与曲线的中心在垂直侧。B) 胶片在照片辐照后进入平整状态的图片 (365 nm, 0.52 W/厘米2)。C) 一幅光线强度太高的胶片的图片, 显示为180°弯曲。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig6large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/56266/56266fig7.jpg"> 
图 7。影片的尖端的机械动摆在时间期间在辐照期间与紫外光 (LED 365 毫微米, 0.52 W/cm2)。镶嵌: 用高速摄影机记录的移动胶片的截图。影片几何是 1.7 cm (长度) x 0.4 cm (宽度) x 20 µm (厚实)。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig7large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/56266/56266fig8.jpg"> 
图 8。暴露区域 (铰链) 的热振荡随着时间的推移在紫外线照射期间 (LED 365 nm, 0.52 瓦特/厘米2).镶片: 带有温度剖面的振荡薄膜的屏幕截图, 它显示了温度在铰链上的变化。影片几何是 1.7 cm (长度) x 0.4 cm (宽度) x 20 µm (厚实)。<a href="//ecsource.jove.com/files/ftp_upload/56266/56266fig8large.jpg" target="_blank">请单击此处查看此图的较大版本.</a>

Watch this Scientific Journal Video about Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light at JoVE.com

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

该协议的目的是创造液晶聚合物薄膜, 可以在连续光照射下机械振荡。我们非常详细地描述了自支撑薄膜的概念, 从液晶对准方法到光驱动。用于制备该材料的实验协议广泛适用。

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 ...

preparation-liquid-crystal-networks-for-macroscopic-oscillatory

Universidad de Cartagena UDEC

Research

Education

JoVE Journal

JoVE Core

Physics

Engineering

Unit 1

Oscillations

SCIENTISTS IN ACTION

11.5K 次观看.  Technical University of Eindhoven. 该协议的目的是创造液晶聚合物薄膜, 可以在连续光照射下机械振荡。我们非常详细地描述了自支撑薄膜的概念, 从液晶对准方法到光驱动。用于制备该材料的实验协议广泛适用。

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

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

光子晶体慢光波导和腔体的制备与表征

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

科研

工程学

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

硅表面润湿性的选择区域改性脉冲紫外激光照射在液体环境

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min&#160;at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

可见光诱导的还原氧化石墨烯的使用电浆纳米粒子

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using ...

Free-form Light Actuators &#8212; Fabrication and Control of Actuation in Microscopic Scale

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted researchers&#39; attention in many fields. Most of the studies focused on macroscopic LCE structures (films, fibers) and their miniaturization is still in its infancy. Recently developed lithography techniques, e.g., mask exposure and replica molding, only allow for creating 2D structures on LCE thin films. Direct laser writing (DLW) opens access to truly 3D fabrication in the microscopic scale. However, controlling the actuation topology and dynamics at the same length scale remains a challenge.
In this paper we report on a method to control the liquid crystal (LC) molecular alignment in the LCE microstructures of arbitrary three-dimensional shape. This was made possible by a combination of direct laser writing for both the LCE structures as well as for micrograting patterns inducing local LC alignment. Several types of grating patterns were used to introduce different LC alignments, which can be subsequently patterned into the LCE structures. This protocol allows one to obtain LCE microstructures with engineered alignments able to perform multiple opto-mechanical actuation, thus being capable of multiple functionalities. Applications can be foreseen in the fields of tunable photonics, micro-robotics, lab-on-chip technology and others.

Here, we fabricate 3D polymeric micro/nano structures in which both the shape and the molecular alignment can be engineered with nanometer scale accuracy by the use of direct laser writing. Light induced deformation of several types of liquid crystalline elastomer microstructures can be controlled in the microscopic scale.

自由形式的光驱动器 - 制作和开动控制在微观尺度

Liquid crystalline elastomers (LCEs) are smart materials capable of reversible shape-change in response to external stimuli, and have attracted ...

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

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

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 ...

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 ...

化学

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 ...

An Electrochemical Cholesteric Liquid Crystalline Device for Quick and Low-Voltage Color Modulation

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The cholesteric LC is composed of a nematic LC 4&#39;-pentyloxy-4-cyanobiphenyl (5OCB), redox-responsive chiral dopant (FcD), and a supporting electrolyte 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm-OTf). The most important component is FcD. This molecule changes its helical twisting power (HTP) value in response to redox reactions. Therefore, in situ electrochemical redox reactions in the LC mixture allow for the device to change its reflection color in response to electrical stimuli. The LC mixture was introduced, by a capillary action, into a sandwich-type ITO glass cell comprising two glass slides with patterned indium tin oxide (ITO) electrodes, one of which was coated with poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) doped with perchlorate (PEDOT+). Upon application of +1.5 V, the reflection color of the device changed from blue (467 nm) to green (485 nm) in 0.4 s. Subsequent application of 0 V made the device recover the original blue color in 2.7 s. This device is characterized by its fastest electrical response and lowest operating voltage among any previously reported cholesteric LC device. This device could pave the way for the development of next generation reflective displays with low energy consumption rates.

A protocol for the fabrication of a reflective cholesteric liquid crystalline display device containing a redox-responsive chiral dopant allowing quick and low-voltage operation is presented.

一种用于快速和低压彩色调制的电化学胆固醇液晶器件

We demonstrate a method for fabricating a prototype reflective display device that contains cholesteric liquid crystal (LC) as an active component. The ...

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 ...