From interparticle forces to macroscopic yielding of soft amorphous solids

从颗粒间力到软无定形固体的宏观屈服

• 批准号: EP/T031077/1
• 负责人: Tanniemola Liverpool
• 金额: $ 67.2万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FT031077%2F1
• 关键词: interparticle; forces; macroscopic; yielding; soft

The response of a material to mechanical loading is one of its most basic properties. Under sufficient load, materials yield and fail, often in a catastrophic fashion. This macroscopic behaviour is ultimately governed by the particles that make up the material - for example, its constituent atoms and molecules. In many applications, one would like to predict a material's macroscopic behaviour, starting from its microscopic constituents. We propose to study the links between microscopic and macroscopic properties of a class of soft materials. These materials are assembled using microscopic particles much bigger than atoms, and interact more weakly. Thus the cohesive forces that hold the particles together are much weaker: the materials are soft and can be easily deformed by mechanical loads. Moreover, in contrast to many familiar materials, the arrangement of the particles is amorphous, and does not resemble the ordered crystals that one typically finds in metals or minerals.This class of material includes gels, as used in products like pesticides, cosmetics, or food. After being prepared, gels degrade with time and eventually become so unstable that they collapse under their own weight. This limits the shelf-life of many products - by analysing the degradation process and linking it to the microscopic behaviour, we hope to inform the design and formulation of future products.Our proposed research will focus on gels formed from emulsions, which consist of microscopic droplets of oil suspended in a watery medium. Milk is an example of such an emulsion. However, the emulsion that we will use has been tailored to allow new kinds of measurement: our emulsion droplets include special fluorescent dye molecules which respond to a mechanical load. We use an extremely powerful microscope (sometimes called a "nanoscope") to see dye molecules at the contact point between two adjacent oil droplets. The more the droplets are squeezed, the brighter the light from the dye molecules.Depending on the experimental conditions, we can assemble these droplets into a network (a gel) or pack them until they almost touch to form a "glass". We will study these amorphous solids, under mechanical load. Together with the dye, our nanoscope will allow us to measure the forces between these microscopic droplets. This kind of measurement has not been possible until now, and will give us vital new information as we analyse the links between the particles' behaviour and the macroscopic properties of the gel.Our experiments will be compared with computer simulations, which provide accurate microscopic descriptions of these materials, without the difficulties associated with imaging small droplets. But there are restrictions on the system sizes and time scales such microscopic simulations access, due to limited computational resources. We will combine simulation and experiment, which provide complementary information - the simulations are accurate on small scales while the experiments reveal the behaviour of macroscopic systems. The experiments will be tested and calibrated against the simulation data.In this way, we answer two kinds of question. First, we understand what happens as a material yields, either under its own weight (gels) or as it flows in response to an external force (glasses). For example, where are the weak points where these materials fail? Can this process be controlled? Second, we will compare our results with theoretical predictions to understand the principles that govern the properties of these materials. Different theories make different assumptions, and make a range of predictions about how amorphous solids yield and flow, and how this depends on their microscopic structure. Our experimental measurement of forces will provide detailed information about these colloidal systems, allowing us to test the theoretical predictions in new ways, and - we hope - to uncover new physical behaviour.

材料对机械载荷的响应是其最基本的特性之一。在足够的载荷下，材料屈服并失效，通常是灾难性的。这种宏观行为最终是由构成材料的粒子控制的——例如，构成材料的原子和分子。在许多应用中，人们希望从材料的微观成分开始预测材料的宏观行为。我们建议研究一类软材料的微观和宏观性质之间的联系。这些材料由比原子大得多的微观粒子组装而成，相互作用也更弱。因此，将颗粒结合在一起的凝聚力要弱得多：材料很软，很容易被机械载荷变形。此外，与许多熟悉的材料不同，这种粒子的排列是无定形的，不像人们通常在金属或矿物中发现的有序晶体。这类材料包括用于杀虫剂、化妆品或食品等产品的凝胶。制备后，凝胶会随着时间的推移而降解，最终变得非常不稳定，在自身重量的作用下会崩溃。这限制了许多产品的保质期-通过分析降解过程并将其与微观行为联系起来，我们希望为未来产品的设计和配方提供信息。我们提议的研究将集中在由乳液形成的凝胶上，它由悬浮在水介质中的微观油滴组成。牛奶就是这种乳剂的一个例子。然而，我们将使用的乳剂已经被定制，以允许新的测量方式：我们的乳剂液滴包含特殊的荧光染料分子，可以对机械负载做出反应。我们使用一种非常强大的显微镜（有时被称为“纳米显微镜”）来观察两个相邻油滴之间接触点上的染料分子。液滴被挤压得越多，染料分子发出的光就越亮。根据实验条件，我们可以将这些液滴组装成一个网络（凝胶），或者将它们包装起来，直到它们几乎接触形成一个“玻璃”。我们将在机械载荷下研究这些无定形固体。与染料一起，我们的纳米显微镜将允许我们测量这些微观液滴之间的力。到目前为止，这种测量还不可能实现，它将为我们分析颗粒行为与凝胶宏观性质之间的联系提供重要的新信息。我们的实验将与计算机模拟进行比较，计算机模拟提供了这些材料的精确微观描述，而没有与小液滴成像相关的困难。但是由于有限的计算资源，系统的大小和时间尺度对微观模拟的访问是有限制的。我们将把模拟和实验结合起来，提供互补的信息——模拟在小尺度上是准确的，而实验揭示了宏观系统的行为。实验将根据模拟数据进行测试和校准。这样，我们就回答了两类问题。首先，我们了解当材料屈服时发生了什么，要么是在自身重量下（凝胶），要么是在外力作用下（玻璃）流动。例如，这些材料的弱点在哪里？这个过程可以控制吗？其次，我们将把我们的结果与理论预测进行比较，以了解控制这些材料性质的原理。不同的理论做出了不同的假设，并对非晶固体的产生和流动以及这如何取决于它们的微观结构做出了一系列预测。我们对力的实验测量将提供有关这些胶体系统的详细信息，使我们能够以新的方式测试理论预测，并且——我们希望——揭示新的物理行为。

项目成果

Direct imaging of contacts and forces in colloidal gels.

• DOI: 10.1063/5.0089276
• 发表时间: 2022-03
• 期刊: The Journal of chemical physics
• 作者: Jun Dong;F. Turci;R. Jack;M. Faers;C. Royall

Rheology of Suspensions of Flat Elastic Particles

扁平弹性颗粒悬浮液的流变学

• DOI: 10.1103/physrevlett.131.194002
• 发表时间: 2023
• 期刊: Physical Review Letters
• 影响因子: 8.6
• 作者: Eggers J

Necking and failure of a particulate gel strand: signatures of yielding on different length scales.

颗粒凝胶链的颈缩和失效：不同长度尺度上的屈服特征。

• DOI: 10.1039/d3sm00681f
• 发表时间: 2023
• 期刊: Soft matter
• 影响因子: 3.4
• 作者: Thijssen K

Active Brownian particles in random and porous environments.

随机和多孔环境中的活性布朗粒子。

• DOI: 10.1063/5.0131340
• 发表时间: 2023
• 期刊: The Journal of chemical physics
• 作者: Moore F

Dynamics and interactions of Quincke roller clusters: From orbits and flips to excited states.

Quincke辊簇的动力和相互作用：从轨道和翻转到激发状态。

• DOI: 10.1126/sciadv.adf5144
• 发表时间: 2023-05-19
• 期刊: SCIENCE ADVANCES
• 影响因子: 13.6
• 作者: Mauleon-Amieva, Abraham;Allen, Michael P.;Liverpool, Tanniemola B.;Royall, C. Patrick
• 通讯作者: Royall, C. Patrick