Physics and Applications of Active Complex Solids

摘要液晶弹性体(LCEs)将向列型和近晶型液晶的纳米级有序结构与橡胶的弱固体特性结合在一起。因此，液晶聚合物中存在取向和分层顺序，这些聚合物被交联以形成这些特殊的橡胶。这种有序性是由化学结合到聚合物中的棒引起的。橡胶和液晶一样，在分子水平上是类似流体的。因此，它能够产生更像液体流动的巨大拉伸。LCEs与经典橡胶相同，只是它们的宏观形状反映了其底层聚合物的各向异性。通过热各向同性到向列相的转变冷却时，它们可以延伸100s%。它们在取暖时会再次收缩。这种变化同样可以通过将光线照射到含有染料的LCE上，然后在黑暗中恢复来诱导。我们将这些光驱动材料称为光弹性体。我们的目标是开发这些用于设备应用的材料，例如利用光驱动来制造新型微流控设备。我们设想的通道可以被光操作的微型阀堵塞，或者由光驱动蠕动泵沿着通道泵送流体。可以将栅格和反射器光学写入LCE薄膜。纳米级与机械性能的耦合也可以来自于其旋转而不是其(暂时)破坏。垂直于有序方向施加的应变可以诱导有序旋转，形状变形以交感方式发生。在胆甾型橡胶中，存在折射率的周期性调制。人们得到了光子能带固体，类似于给人半导体的电子能带固体。在橡胶中，这些是可变形的光子带结构，结果是人们得到了机械移动的激光颜色。这项建议的一个目的是了解如何使这些带状固体更适合于可调谐激光设备。层状液晶(Smectics)生产的橡胶具有更丰富的性能。它们的机械响应在其层的2维空间是橡胶的，在3维空间是固体的。在它们倾斜的手性形式中，它们是软固体铁电，也就是说，它们具有自发电极化的方向。它们作为铁电材料的独特之处在于，它们在当地是液体状的，而不是非常坚硬的陶瓷。它们的偏振方向可以被诱导旋转，以响应特定的剪切。相反，施加电场会导致极化方向旋转，从而产生剪切力。前者可以是传感器，后者可以是执行器。我们的目标是开发这些材料作为器件。我们编写了液晶弹性体(OUP，2003)，这已经成为该领域的标准研究专著。第一章(连同内容和前言)可在网站(http://www.tcm.phy.cam.ac.uk/~mw141/))上找到，并为非专业受众总结了我们旨在探索其材料和设备潜力的效果。在同一页上有热驱动胶片和折弯机(两者都是热光弹性体)的链接。

SummaryLiquid crystal elastomers (LCEs) combine the nano-scale order of nematic and smectic liquid crystals, with the weak solid character of rubber. Thus there is orientational and layering order in the liquid crystalline polymers that are crosslinked to form these special rubbers. The ordering arises from the rods that are incorporated chemically into the polymers. Rubber, like liquid crystals, is fluid-like at the molecular level. It is thus capable of huge extensions that are more like the flow of a liquid.LCEs are the same as classical rubber, except that they take a macroscopic shape that reflects the anisotropy of their underlying polymers. They can extend by 100s% when cooling through the thermal isotropic to nematic transition. They contract again on heating. Such changes can be equally induced by shining light onto dye-containing LCEs, with subsequent recovery in the dark. We called these light actuated materials photo-elastomers.We aim to develop these materials for device applications, for instance actuation by light to make new types of microfluidic devices. We envisage channels that can be blocked by a light-operated micro-valve, or fluid pumped along channels by a light-driven peristaltic pump. Gratings and reflectors could be optically written into LCE films.The coupling of nano-order to mechanical properties can also be from its rotation instead of by its (temporary) destruction. Strains applied perpendicular to the ordering direction can induce the order to rotate, with shape deformations occurring sympathetically. In cholesteric rubber there is a periodic modulation of the refractive index. One gets a photonic band solid, analogous to an electronic band solid that gives one semi-conductors. In rubber these are deformable photonic band structures, with the consequence one gets a mechanically shifting laser colour. An object of this proposal is to understand how to make these band solids more perfect for tunable laser devices.The layered liquid crystals (Smectics) yield rubbers with even richer behaviour. Their mechanical response can be rubbery in the 2-dimensions of their layers, and solid-like in the third. In their tilted, chiral form, they are soft solid ferro-electrics, that is they have a direction of spontaneous electric polarisation. They are unique as ferro-electrics in that they are liquid-like at the local level, rather than being very hard ceramics. Their polarisation direction can be induced to rotate in response to particular shears. Inversely, applying an electric field causes the polarisation direction to rotate and hence shears to develop. The former could be a sensor, the latter an actuator. We aim to exploit these materials as devices.We have written Liquid Crystal Elastomers (OUP, 2003) which has become the standard research monograph in the field. The first chapter (along with the contents and preface) is available on the web (http://www.tcm.phy.cam.ac.uk/~mw141/) and summarises for a non-specialist audience the effects we aim to explore for their materials and device potential. There are links on the same page to films of thermal actuation, and to benders (both thermo- photo-elastomeric).