Photo-Switchable Surface Topologies in Chiral Nematic Coatings
Photo-Switchable Surface Topologies in Chiral Nematic Coatings
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DOI：
10.1002/anie.201105101
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Broer, Dirk J.
中科院分区：
文献类型：
--
作者：
Liu, Danqing;Bastiaansen, Cees W. M.;Broer, Dirk J.
通过两种状态之间的主动切换来控制微米范围内的表面拓扑结构对于各种应用都很有意义。例如，摩擦系数的拓扑调制变化在触觉领域得到了应用，其中机器人操作和触摸输入设备非常重要。 [1]此外，光学特性还受到表面拓扑变化的强烈影响，例如，漫反射的方向性[2]或衍射特性的调制。我们还可以考虑更先进的应用，例如可切换的润湿性或粘附控制，例如壁虎攀爬表面引起的粘附。此外，在微流体应用中，通过在表面引入微观拓扑结构可以大大增强扩散和流体混合。 [3]在许多当前的实现中，表面拓扑的切换是利用静电或压电效应由电场触发的。[4]这需要直接靠近电极和电线来驱动该过程。或者，可以使用基于热膨胀效应 [5] 或相变的热效应。 [6]在缓冲溶液中，表面转换是通过 pH 或热效应在水凝胶中建立的，并且通常被提议用于控制生物系统中的蛋白质或细胞粘附。 [7]在这里，我们将使用光来动态驱动表面浮雕。使用光有几个优点。可以远程处理表面，避免制造电极结构或用于局部加热的特殊装置。它还避免了用于膨胀和消膨胀的缓冲溶液的存在。此外，它可以通过聚焦或图案化曝光进行局部引导。文献中报道了含偶氮苯的线性聚合物，它们基于光驱动的材料传输形成表面浮雕。[8, 9] 这些材料已被广泛研究，并被提议用于全息光栅和光学数据存储。该系统在激光照射下运行，原则上是可重写的，尽管这很复杂，因为需要第二次曝光。在这里，我们提出了一种新方法来动态调节在相对较低的光强度条件下运行的涂层的表面拓扑结构。该原理基于分子有序参数变化时液晶网络的各向异性几何变化。液晶网络是通过单片取向状态下的多官能液晶单体的原位光聚合获得的。[10, 11] 聚合后，单体秩序得以维持，并形成复杂的导向图案
Control of the surface topology in the micrometer range by active switching between two states is of interest for a wide variety of applications. For instance, a topology-modulated change in the friction coefficients finds its application in the field of haptics where robotic manipulation and touch-input devices are of importance.[1] Also the optical properties are strongly affected by changes of the surface topology, for example, the directionality of diffusive reflection [2] or the modulation of diffractive properties. We can also think of even more advanced applications such as switchable wettability or adhesion control as, for example, the adhesion induced by geckos climbing surfaces. Furthermore, in microfluidic applications diffusion and fluid mixing can be substantially enhanced by introducing microscopic topologies on the surface.[3] In many current implementations the switching of the surface topology is triggered by an electric field using electrostatic or piezoelectric effects.[4] This requires the direct vicinity of electrodes and wires for driving the process. Alternatively, thermal effects based on thermal expansion effects [5] or phase transitions can be used.[6] In buffer solutions surface switching is established in hydrogels by either pH or thermal effects and is often proposed to control protein or cell adhesion in biological systems.[7] Here, we will use light for the dynamic actuation of a surface relief. The use of light has several advantages. The surfaces can be addressed remotely avoiding the fabrication of electrode structures or special means for localized heating. It also avoids the presence of a buffer solution for swelling and deswelling. Moreover, it can be directed locally by focused or patterned exposure. In the literature azobenzenecontaining linear polymers are reported that form surface reliefs based on light-driven material transport.[8, 9] These materials have been widely studied and are proposed for holographic gratings and optical data storage. The system operates under exposure to laser light and is in principle rewritable although this is complex because a second exposure is needed.Here, we propose a new method to modulate dynamically the surface topology of a coating that operates under conditions of relatively low light intensity. The principle is based on anisotropic geometric changes of a liquid-crystal network upon a change of the molecular order parameters. Liquid-crystal networks are obtained by in situ photo-polymerization of a polyfunctional liquid-crystal monomer in its monolithically oriented state.[10, 11] Upon polymerization the monomer order is maintained and complex director patterns