Edinburgh Soft Matter and Statistical Physics Programme Grant Renewal

“软物质”一词描述了一组材料，这些材料由尺寸为微米或纳米级的组件组装而成，比典型的分子或原子大得多。例子包括聚合物（非常长的柔性分子）、胶体（小的硬球体）、乳液（一种流体中的水滴）、泡沫（流体中的气泡）、洗涤剂分子（具有亲水的头部和憎水的尾部——这些分子聚集在一起形成复杂的形状）、粉末（小的干燥颗粒）和许多生物起源的类似系统。熟悉的例子分别是发动机油、油漆、蛋黄酱、剃须膏、洗发水和滑石粉；生物类似物包括黏液、黏菌、唾液和活细胞的各种成分。在许多情况下，系统的行为不是由其组成部分的化学细节控制的，而是由它们的物理相互作用控制的，这对每一类材料都是通用的。与（比如说）一块金属相比，这些材料之所以柔软，是因为它们之间的相互作用通常比原子之间的相互作用弱。这使得弯曲和塑造材料变得容易，并使它们受到极端流动（导致结构破坏），这是金属或其他形式的“硬”凝聚态物质无法轻易实现的。相互作用的弱点意味着即使在室温下也有很多随机运动（我们称之为热的运动）；软材料的特性通常更接近于通过最大化系统的熵（随机性）而不是最小化系统的能量而得到的特性。在这些条件下，人们必须使用“统计力学”的工具来理解微观的相互作用是如何结合熵来决定材料的性质的。爱丁堡软物质和统计物理小组开发了实验和理论技术，以了解软材料的成分是如何决定其性质的，特别是那些与材料流动有关的性质（“流变学”科学）。我们的工作重点是对少数模型系统进行详细的研究，每个模型系统都代表一个更大的类别：通过深入了解这些系统，我们希望通过对更大范围的样本整理更肤浅的结果来找到可能不明显的一般原则。我们希望继续我们的实验和理论的综合方案，以解决软凝聚态物质的新课题，越来越多的那些在与生物学的界面。五个主要项目是：1。流变物理学-了解胶体和其他软材料在强流动条件下的行为。通常，流动可以完全改变这些材料的内部结构，我们想要了解这一点。软物质和生物学中的障碍物理学——了解软物质和生物系统如何经历“罕见事件”，将它们从一个明显稳定的组织状态转移到另一个组织状态。这包括改变基因在细胞中表达方式的事件，也包括物质的一个阶段在另一个阶段成核。新的软材料——在我们最近发现的基础上，我们想用物理学来创造新的、有趣的材料，这些材料的性能可能与计算机显示、药物输送、催化和其他领域有关。细胞运动的物理学——我们想了解细菌（如果它们死了，实际上就是胶体）在单独或集体（成群）游泳时的行为。在较小的范围内，细胞内有各种软物质成分，它们使用不断供应的化学能来维持“活跃”（即生命）状态。我们也想了解这些。新的统计力学工具——我们希望开发新的更好的理论和模拟模型，从长远来看，这些理论和模型将帮助我们将软材料中的微观成分与其宏观特性联系起来。

The term 'soft matter' describes a group of materials that are assembled from components whose size scale is of order microns or nanometers -- much bigger than a typical molecule or atom. Examples include polymers (very long flexible molecules), colloids (small hard spheres), emulsions (droplets of one fluid in another), foams (gas bubbles in a fluid), detergent molecules (with a water-loving head and a water-hating tail -- these clump together into complex shapes), powders (small dry grains), and many analagous systems of biological origin. Familiar examples are respectively engine oil, paint, mayonnaise, shaving cream, shampoo, and talc; the biological analogues include mucus, slime moulds, saliva, and various components of the living cell.In many cases, the system's behaviour is controlled not by the chemical details of its components, but by their physical interactions, which are generic to each class of material. The softness of these materials, compared to (say) a piece of metal, arises from the fact that these interactions are generically weaker than those between atoms. This makes it easy to bend and shape the materials, and to subject them to extremes of flow (causing disruption to the structure) that cannot easily be achieved with metals or other forms of 'hard' condensed matter. The weakness of the interactions means that there is a lot of random motion (the motion we call heat) even at room temperature; the properties of soft materials are often closer to those found by maximising the entropy (randomness) of the system than to those found by minimizing its energy. Under these conditions, one must use the tools of 'statistical mechanics' to understand how the microscopic interactions, combined with entropy, come to determine the properties of the material.The Edinburgh Soft Matter and Statistical Physics Group has developed experimental and theoretical techniques for understanding how the ingredients of a soft material come to determine its properties -- particularly those properties related to how the material flows (the science of 'rheology'). Our work focusses on making detailed studies of a small number of model systems, each representative of a larger class: by understanding these in depth, we hope to find general principles that might not be obvious by collating more superficial results for a wider range of samples. We wish to continue our integrated programme in experiment and theory, to address new topics in soft condensed matter, increasingly those at the interface with biology. The five main projects are:1. Rheophysics -- to understand the behaviour of colloids and other soft materials under conditions of strong flow. Often, flow can totally alter the internal structure of such materials and we want to understand this.2. Physics of barriers in soft matter and biology -- to understand how soft and biological systems undergo 'rare events' taking them from one apparently stable state of organization to another. These include events that alter the way genes are expressed in a cell, and also the nucleation of one phase of matter within another.3. New soft materials -- building on our recent discoveries, we want to use physics to create new and interesting materials with properties potentially relevant to computer displays, drug delivery, catalysis and other fields.4. Physics of cellular motion -- we want to understand how bacteria (which, if they were dead, would be effectively colloids) behave when swimming, either individually, or collectively (in a swarm). At a smaller scale, within the cell there are various soft matter components which use a constant supply of chemical energy to maintain an 'active' (i.e. living) state. We want to understand these too.5. New statistical mechanics tools -- we want to develop new and better theories and simulation models that will, over the longer term, help us connect the microscopic components in soft materials to their macroscopic properties.