Quantitative Theory for Polyelectrolyte and Liquid-Crystalline Brushes

聚合物刷子是指表面密集涂覆聚合物分子，每个分子通过其一端附着在表面上。刷子提供了一种简单而通用的方法来修改表面特性，如摩擦、附着力和润湿行为。可以实现这一点的聚合物材料的丰富选择提供了不同范围的表面涂层。有了新的合成技术，现在有可能创造出令人印象深刻的精确度和日益复杂的刷子，同样，最先进的实验能够以前所未有的细节测量它们的特性。另一方面，笔刷理论在过去几十年中进展甚微。为了跟上实验的步伐，目前的建议旨在发展先进的理论，能够做出准确的定量预测。拟议的研究将主要集中在聚合物链带电的聚电解质刷子上。它们最耐人寻味的特性之一是当两个相对的刷子相互滑动时产生的超小(几乎无法测量)摩擦，即使它们在几个大气压的压力下相互推动也是如此。似乎大自然本身就利用了这一特性，在哺乳动物关节的外软骨表面涂上了生物聚电解质聚合物。因此，人们可以想象对人工髋关节或膝关节做同样的事情。聚电解质刷还有另一个有用的特性，即它们可以自发地从伸展状态切换到塌陷状态；这在新兴的纳米技术领域具有许多潜在的应用，包括建造超小型设备。例如，这种转变可用于制造小型马达(即致动器)或打开和关闭(即浇口)小孔膜。这种转变可以由温度、pH值的变化(对于浸入水中的刷子)或通过施加外部电场来诱导。这项研究还将研究液晶刷子的行为，其中聚合物链的长度上附着着小的介元单元。潜在的用途包括具有电光、机械光学和机电行为的智能响应表面。还有一种理论计算预测，介元单元的排列可能会导致电刷坍塌，导致类似于具有类似潜在应用的聚电解质电刷的转变。同样，我们应该能够通过改变温度或施加电场来诱导这种转变。也有充分的理由相信，液晶电刷将在液晶显示器(LCD)中具有优异的性能，它们还可能为有机半导体提供重要的元件。

Polymeric brushes refer to surfaces densely coated with polymer molecules, each attached to the surface by one of their ends. Brushes offer an easy and versatile way of modifying surface properties, such as friction, adhesion and wetting behaviour. The rich selection of polymeric materials with which this can be done provides a diverse range of surface coatings. With new synthetic techniques it is now becoming possible to create brushes of impressive precision and ever increasing complexity, and likewise state-of-the-art experiments are able to measure their properties with unprecedented detail. On the other hand, brush theories have advanced very little over the last couple decades. To keep pace with experiments, the present proposal aims to develop advanced theories with the capability of making accurate quantitative predictions.Much of the proposed research will focus on polyelectrolyte brushes in which the polymer chains become electrically charged. One of their most intriguing properties is the ultra-small (almost unmeasurable) friction that occurs when two opposing brushes slide past each other, even when they are pushed against each other at a pressure of several atmospheres. It seems that nature itself makes use of this property by coating the outer cartilage surface of mammalian joints with biological polyelectrolyte polymers. Thus one could imagine doing the same with artificial hip or knee joints. Polyelectrolyte brushes also have another useful property that they can spontaneously switch from an extended state to a collapsed state; this has a number of potential applications in the emerging field of nano-technology, which involves the building of ultra-small devices. For instance, this transition can be used to create small motors (i.e., actuators) or to open and close (i.e., gate) small porous membranes. The transition can be induced by changes in temperature, the pH (for brushes immersed in water), or by the application of an external electric field.This research will also investigate the behaviour of liquid-crystalline brushes, where the polymer chains have small mesogen units attached along their length. Potential uses include smart responsive surfaces with electro-optic, mechano-optic and electro-mechanic behaviours. There is also a theoretical calculation predicting that the alignment of the mesogens units can cause the brush to collapse, causing an analogous transition to that of the polyelectrolyte brushes with similar potential applications. Again, we should be able to induce the transition by changing temperature or by applying an electric field. There are also good reasons to believe that liquid-crystalline brushes will have superior properties for liquid-crystal displays (LCD's), and they may also provide important components for organic semi-conductors.