Liquid Crystal Elastomers: from new material, via new mechanics to new machines

机械机器的核心是一种移动和改变形状的装置。例如，照相机包含按快门、延长镜头和扩大光圈的机器，汽车包含转向时转动车轮的机器。然而，传统的工程材料，如钢和塑料，是刚性的，所以机器必须通过将许多刚性元件组合成一个复杂的机构来构建，该机构需要滑动关节（铰链，轴，枢轴等），以允许形状变化。相反，生物学用肌肉制造机器，肌肉是一种活跃的工作材料，不仅可以变形，而且可以主动改变形状。例如，心脏完全由肌肉构成，通过挤压和扩张心室来输送血液。这种方法消除了复杂的机制，产生了简单可靠的机器，通常只有一个部件：肌肉就是整个机器。这个项目是关于用人造肌肉建造机器，在人体工程中复制生物学的方法。这项工作是由于发现了一种新的人造肌肉——液晶弹性体（LCEs）。它们是柔软的橡皮筋状固体，但在分子水平上，它们是由微小的刚性杆构成的，所有这些杆都指向同一个方向。如果LCE被加热或照射，它就会沿着这个“对齐”方向收缩，就像肌肉沿着纤维方向收缩一样。收缩是非常大的，可逆的，可以用来施加一个大的拉力。如此大而简单的收缩已经令人印象深刻。更棒的是，lce现在可以通过编程的空间对齐模式来制作。当这些材料被加热或照亮时，就会产生一种收缩模式，从而使材料变形成一种新的、潜在的复杂形状。例如，一个具有同心圆收缩环的LCE圆盘会变成一个锥体，当它变形时，它可以举起一个大的重物，或者做其他的机械工作。因此，lce是可编程的机械机器。该项目从如何编程lce以产生所需形状变化的基本问题开始。我们首先要问的是，用给定的收缩模式编程的LCE实际上是如何改变形状的。然后，我们转向更困难的问题，即设计使LCE变形成所需形状所需的收缩模式。我们将在三种不同的LCE系统中解决这些问题：变形为弯曲外壳的平板，变形为平面上的浮雕/地形的智能涂层，以及变形为不同3d形状的3d打印形状。我们的方法将理论和计算结合在一起，通过实际的LCE制造来设计模式和预测形状变化，以测试和验证我们的设计。以这种方式将预测和测试结合在一起，将创建一个独特的集成LCE工程团队，实现快速进展，并允许我们制作真实机器的原型。事实上，从最早的阶段开始，我们将设计做机械工作的模式化LCE，并制造LCE机器。首先是升降机：我们将研究如何对平板进行编程，以便在加热/照明时，它变成具有最大升降能力的3-D锥形外壳。接下来将是盲文像素的智能涂层，它在照明下从平面变成疙瘩。从这里开始，这是迈向全盲文显示器的一小步。更有野心的是，我们将设计智能表面，在加热/照明方面获得设计师的缓解，目标是出现标识的安全贴纸。我们的最终目标（与Knowles集团和流体分析合作）是商用LCE微流体——使用LCE构建微型管道系统，以微小规模复制实验室的全部功能。我们将设计由光控制/驱动的LCE阀和泵，并将它们集成到微流控系统中，克服微流控电路复杂性的关键瓶颈。

A mechanical machine, at its heart, is a device that moves and changes shape. E.g. a camera contains machines to click the shutter, extend the lens and dilate the aperture, and a car contains a machine to turn the wheels when steering. However, traditional engineering materials, such a steel and plastic, are rigid, so machines have to be constructed by combining many rigid elements into a complex mechanism with sliding joints (hinges,axels,pivots etc) needed to allow shape change at all. In contrast, biology builds machines out of muscle, an active working material that can not only be deformed, but can itself actively change shape. For example, a heart is built entirely out of muscle, and pumps blood by squeezing and dilating its chambers. This approach eliminates complex mechanisms, and leads to simple reliable machines, often with just a single part: the muscle is the entire machine.This project is about building machines with artificial muscles, reproducing biology's approach in human engineering. The work is enabled by the discovery of a new class of artificial muscle, liquid crystal elastomers (LCEs). These are soft rubber-band like solids, but at a molecular level they are built out of tiny rigid rods, and all these rods point in the same direction. If the LCE is heated or illuminated, it contracts along this "alignment" direction, just like a muscle contracts along its fiber direction. The contraction is dramatically large, reversible, and can be used to exert a large pulling force. Such large-but-simple contractions are already impressive. Even better, LCEs can now be made with a spatial pattern of alignment programmed into them. When these are heated/illuminated, this encodes a pattern of contraction, which morphs the material into a new, potentially complex, shape. For example, an LCE disk with concentric rings of contraction will morph into a cone, and, as it morphs, it can lift a large weight, or do other mechanical work. LCEs are thus programmable mechanical machines.This project starts with fundamental questions about how to program LCEs to produce desired shape changes. We start by asking how an LCE programmed with a given pattern of contraction will actually change shape. We then move to the more difficult problem of designing the pattern of contraction required to make an LCE morph into a desired shape. We will solve these problems in three different LCE systems: flat sheets that morph into curved shells, smart coatings that morph to create relief/topography on a flat surface, and 3-D printed shapes that morph into different 3-D shapes. Our approach draws together theory and computations, to design patterns and predict shape changes, with actual LCE fabrication, to test and validate our designs. Bringing prediction and testing together in this way will create a unique integrated LCE engineering group, enable rapid progress, and allow us to prototype real machines.Indeed, from the earliest stages, we will be designing patterned LCEs that do mechanical work, and making LCE machines. First will be lifters: we will work out how to program a flat sheet so that, on heating/illumination, it morphs into a 3-D cone type shell with maximum lifting ability. Next will be a smart-coating of braille pixels which morph from flat to pimple on illumination. From here, it is a small step to a full braille display. More ambitiously, we will design smart surfaces which acquire designer relief on heating/illumination, targeting a security sticker on which a logo appears. Our ultimate target, (collaborating with the Knowles group and fluidic analytics) is commercial LCE microfluidics - using LCEs to build tiny plumbing systems, that replicate the full functionality of a laboratory at a tiny scale. We will design LCE valves and pumps which are controlled/powered by a light, and incorporate them into microfluidic systems, overcoming a key bottleneck in the complexity of microfluidic circuits.