Edinburgh Soft Matter and Statistical Physics Programme Grant Renewal

软物质这个术语描述的是一组材料，这些材料由尺寸在微米或纳米量级的组件组装而成，比典型的分子或原子要大得多。例如聚合物(非常长的柔性分子)、胶体(小的硬球)、乳剂(一种液体的液滴在另一种液体中的液滴)、泡沫(液体中的气泡)、洗涤剂分子(有一个爱水的头和一个讨厌水的尾巴--这些聚集在一起形成复杂的形状)、粉末(小的干燥颗粒)和许多类似的生物起源的系统。常见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；生物类似物包括粘液、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成分的化学细节控制的，而是由它们的物理相互作用控制的，这些相互作用对于每一类材料都是通用的。与一块金属相比，这些材料的柔软性源于这样一个事实，即这些相互作用通常比原子之间的相互作用弱。这使得材料很容易弯曲和成形，并使它们受到极端流动(导致结构破坏)的影响，而金属或其他形式的“硬”凝聚物质不容易实现这一点。相互作用的弱点意味着，即使在室温下，也会有大量的随机运动(我们称之为热的运动)；软材料的性质往往更接近于通过最大化系统的熵(随机性)所发现的性质，而不是通过最小化其能量所发现的性质。在这种情况下，人们必须使用统计力学的工具来了解微观相互作用和熵是如何决定材料的性质的。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如何决定其性质--特别是那些与材料如何流动有关的性质(流变学科学)。我们的工作集中于对少数模型系统进行详细研究，每个模型系统代表一个更大的类别：通过深入了解这些系统，我们希望通过整理更广泛样本的更肤浅的结果来找到可能不明显的一般原理。我们希望继续我们在实验和理论方面的综合计划，以解决软凝聚态物质的新课题，越来越多地涉及与生物学的界面的那些课题。这五个主要项目是：1.流变学--了解胶体和其他软材料在强流条件下的行为。通常，流动可以完全改变这种材料的内部结构，我们想要了解这一点。软物质和生物障碍的物理学--理解软物质和生物系统如何经历罕见事件，将它们从一种表面上稳定的组织状态转移到另一种组织状态。这些事件包括改变基因在细胞中表达方式的事件，以及物质在另一阶段的成核。新的软材料--在我们最近发现的基础上，我们希望利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、催化和其他领域相关。细胞运动物理学--我们想要了解细菌(如果它们死了，实际上就是胶体)在游泳时的表现，无论是单独的，还是集体的(在群体中)。在较小的尺度上，细胞内有各种软物质成分，它们使用持续的化学能量供应来维持一种“活跃”(即活的)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，这将帮助我们将软材料中的微观成分与它们的宏观性质联系起来。

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.