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Dynamic arrest and non-equilibrium behaviour in suspensions of deformable colloids

可变形胶体悬浮液中的动态停滞和非平衡行为

基本信息

批准号：
EP/J02113X/1
负责人：
Karl Johan Linus Mattsson
金额：
$ 12.79万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ02113X%2F1
关键词：
Dynamic arrest non equilibrium behaviour

项目摘要

The molecules of a liquid move easily and a snap-shot of the molecular arrangements reveal complete disorder. As a liquid is cooled, it often undergoes crystallization, where the molecules arrange into an ordered pattern. The most common example is water turning into ice. However, such crystallization can be avoided by cooling at a fast rate. The liquid molecules then move slower and slower upon cooling and if the cooling rate is high enough there is not enough time to rearrange into an ordered pattern before all long-range motions come to a halt; thus, the structure remains disordered and liquid-like but the material is hard - the resulting solid is called a glass. Glassy materials are important in a wide range of man-made materials and applications including battery electrolytes and electrodes, solar cells, pharmaceuticals and most plastics. Neither the microscopic mechanisms involved in glass-formation nor the behaviour of the glassy state are well understood; this is remarkable since humans have been producing glass for thousands of years and glasses have been naturally formed by geological processes for millions of years. Thus, reaching an understanding of glasses and their formation is a key unsolved problem in both fundamental science and technology. Remarkably, an analogy can be drawn between and the molecules (size: 0.1-10 nm) of molecular glass-formers and the behaviour of particles (size: 0.1-10 microns) suspended in a liquid, so called colloids. For colloids, glass-formation is controlled by the concentration of particles within a certain volume; for low particle concentrations the system is a liquid but as the concentration is increased the system gets crowded, which leads to the formation of a glass. Practical examples include paints, emulsions, lubricants and thickeners. The advantage of using colloids as a model system to study glass-formation is the large particle size, which means that the colloid motions can be studied using light as a probe, together with the great control of properties such as colloid size, elasticity and inter-particle interactions. In this work we will use a versatile colloidal model system consisting of gel particles swollen in a solvent, so called microgels. In addition to their role as model systems, such microgel suspensions are important in applications including biosensing and medical diagnostics, chemical separation technologies, oil recovery, pharmaceutical delivery, and switchable materials.We will synthesize microgel particles with varying mechanical properties, by controlling the cross-linking of the particle gels. Each microgel batch will be characterized with regards to particle size, gel structure and mechanical properties. We will then study how these microgel suspensions form glasses as the particles crowd the volume upon concentration. Both the arrangement and the motions of the microgel particles will be studied as the glassy state is approached, using light scattering and rheology techniques. Light scattering studies yield information about the individual microgel structure, the microgel particle arrangements and the microgel motions over a wide range of time-scales (10 ns-1000 s). With rheology, the response of the material to a mechanical disturbance is investigated. Specific aims of the study are to (i) find the relationship between single microgel properties and the corresponding suspension arrangements and motions as the glassy state is approached (ii) determine which types of microgel motions are relevant to the glass formation process and how these motions are inter-related (iii) investigate how an applied shear affects and eventually 'melts' a microgel glass.This work addresses questions that are key to an understanding of glassy materials in general. By systematic studies of an excellent model system, we aim to form a benchmark for future glass-transition work.

液体的分子很容易移动，分子排列的快照显示出完全的无序。当液体被冷却时，它经常经历结晶，其中分子排列成有序的图案。最常见的例子是水变成冰。然而，这种结晶可以通过快速冷却来避免。然后，液体分子在冷却时移动得越来越慢，如果冷却速率足够高，在所有长距离运动停止之前，没有足够的时间重新排列成有序的模式;因此，结构保持无序和液体状，但材料是坚硬的-产生的固体被称为玻璃。玻璃质材料在广泛的人造材料和应用中非常重要，包括电池电解质和电极、太阳能电池、药品和大多数塑料。无论是玻璃形成的微观机制还是玻璃态的行为都没有得到很好的理解;这是值得注意的，因为人类已经生产了数千年的玻璃，玻璃已经通过地质过程自然形成了数百万年。因此，对玻璃及其形成的理解是基础科学和技术中尚未解决的关键问题。值得注意的是，可以在分子玻璃形成物的分子（尺寸：0.1-10 nm）和悬浮在液体中的颗粒（尺寸：0.1-10微米）（所谓的胶体）的行为之间进行类比。对于胶体，玻璃的形成由一定体积内的颗粒浓度控制;对于低颗粒浓度，系统是液体，但随着浓度的增加，系统变得拥挤，这导致玻璃的形成。实例包括油漆、乳剂、润滑剂和增稠剂。使用胶体作为模型系统来研究玻璃形成的优点是大颗粒尺寸，这意味着可以使用光作为探针来研究胶体运动，以及对诸如胶体尺寸、弹性和颗粒间相互作用等性质的极大控制。在这项工作中，我们将使用一个多功能的胶体模型系统组成的凝胶颗粒在溶剂中溶胀，所谓的微凝胶。除了作为模型系统的作用外，这种微凝胶悬浮液在生物传感和医学诊断、化学分离技术、石油开采、药物输送和可转换材料等应用中也很重要。我们将通过控制颗粒凝胶的交联来合成具有不同机械性能的微凝胶颗粒。将对每个微凝胶批次的粒度、凝胶结构和机械性能进行表征。然后，我们将研究这些微凝胶悬浮液如何形成玻璃，因为颗粒在浓缩时聚集在体积中。微凝胶颗粒的排列和运动将被研究为接近玻璃态，使用光散射和流变学技术。光散射的研究产生的信息的个别微凝胶结构，微凝胶颗粒的安排和微凝胶运动在很宽的时间尺度（10纳秒-1000秒）。利用流变学，研究材料对机械扰动的响应。研究的具体目的是（i）发现单个微凝胶性质与接近玻璃态时相应的悬浮排列和运动之间的关系（ii）确定哪种类型的微凝胶运动与玻璃形成过程相关以及这些运动是如何相互关联的（iii）研究外加剪切力如何影响并最终“熔化”微凝胶玻璃。2这项工作解决了一些问题，这些问题是理解一般玻璃质材料的关键。通过对一个优秀的模型系统的系统研究，我们的目标是为未来的玻璃化转变工作形成一个基准。