Rheology revealed by microscopic rotation: orientation fluctuations, friction and mechanics in colloidal gels

微观旋转揭示的流变学：胶体凝胶中的取向波动、摩擦和力学

• 批准号: 2226485
• 负责人: Jeffrey Urbach
• 金额: $ 69.2万
• 依托单位: Georgetown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-01-15 至 2025-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2226485&HistoricalAwards=false
• 关键词: Rheology; revealed; microscopic; rotation; orientation

Non-technical abstract:Soft solids formed from particle gels are found in a wide range of materials, with applications ranging from consumer products to bio-manufacturing and additive manufacturing. Despite their importance, we lack a fundamental understanding of the connection between the microscopic structure and dynamics of the particles and the macroscopic mechanical properties of the gel. As a result, we have only limited capacity to predict basic properties like gel stiffness and ultimate strength even with detailed knowledge of the particle properties and of the solvent in which they are immersed. This, in turn, limits our ability to engineer gel properties. In this work we will use a suite of novel tools to reveal, for the first time, the dynamics of rotations of individual particles, and use this information to determine how the particles assemble into networks that support forces and determine the stiffness and strength of the gels. We will use these insights to develop robust pathways to engineering materials with defined properties and support the design of tunable and adaptive materials for applications such as self-healing, stimuli-responsive materials, and materials for 3D printing. In addition, this project will support efforts to harness soft materials to address the profound challenges of sustainability by strengthening contacts between the soft matter research community and policy makers.Technical abstract:Particle-resolved studies of gels formed when micron-scale colloidal particles interact via short ranged attraction, mediated by the depletion interaction, have provided a wealth of information and considerable insight into the connection between gel microstructure and mechanical properties. However, much of this work is limited by the inability to directly assess particle-scale interactions and dynamics in the gel state. This project employs novel colloidal particles containing an off-center core that allows for precise determination of the orientation of each particle by fluorescence microscopy, in combination with advanced instrumentation that allows for simultaneous high speed confocal imaging and rheology. The project leverages the fact that the orientation dynamics of the particles provide a very sensitive measure of interparticle interactions, and in particular, that monitoring the rotational Brownian motion of individual particles reveals a transition from rotationally mobile to arrested states as the strength of the depletion interaction is increased. In this research, the PIs exploit the local information provided by this transition to address fundamental questions about the links between microscopic heterogeneity and macroscopic rheology. Complementary computer simulations, building on an existing platform that reproduces many aspects of particle gel rheology, inform and are informed by the experimental results. The research also exploits Boundary Stress Microscopy, a technique developed by the PIs enabling measurement of local stresses at the boundary of a sheared gel with high spatial and temporal resolution, to directly connect particle interactions to mesoscale stress heterogeneity. The impact of surface modifications that change interparticle friction on the rotational dynamics-rheology connection will also be assessed. The insights from these measurements are used to develop and validate computational models, which in turn guide the development of predictive models connecting micro- and meso-scale material heterogeneities to their macroscopic mechanics. The research is disseminated through the network maintained by the Institute for Soft Matter Synthesis and Metrology at Georgetown, including the semi-annual Mid-Atlantic Soft Matter Workshops, and connects to an initiative to integrate Sustainable Materials into efforts at Georgetown’s newly formed Earth Commons Institute for Environment and Sustainability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

非技术摘要：由颗粒凝胶形成的软固体广泛存在于各种材料中，应用范围从消费品到生物制造和增材制造。尽管它们很重要，但我们对颗粒的微观结构和动力学与凝胶的宏观力学性能之间的联系缺乏基本的理解。因此，即使我们详细了解了颗粒的性质和浸入其中的溶剂，我们预测凝胶硬度和最终强度等基本性质的能力也很有限。这反过来又限制了我们设计凝胶特性的能力。在这项工作中，我们将使用一套新颖的工具来揭示，第一次，单个粒子的旋转动力学，并利用这些信息来确定粒子如何组装成支持力的网络，并确定凝胶的刚度和强度。我们将利用这些见解开发具有定义属性的工程材料的强大途径，并支持可调和自适应材料的设计，用于自修复，刺激响应材料和3D打印材料等应用。此外，该项目将通过加强软物质研究界与政策制定者之间的联系，支持利用软材料解决可持续发展的深刻挑战。技术摘要：对微米级胶体粒子通过耗损相互作用介导的短程吸引相互作用形成的凝胶进行粒子解析研究，为凝胶微观结构与力学性能之间的联系提供了丰富的信息和相当大的见解。然而，由于无法直接评估凝胶状态下粒子尺度的相互作用和动力学，许多工作受到限制。该项目采用了新型胶体颗粒，其中包含一个偏离中心的核心，可以通过荧光显微镜精确确定每个颗粒的方向，并结合先进的仪器，可以同时进行高速共聚焦成像和流变学。该项目利用了这样一个事实，即粒子的方向动力学提供了一个非常敏感的粒子间相互作用的测量，特别是，监测单个粒子的旋转布朗运动揭示了随着耗尽相互作用强度的增加，从旋转移动到停滞状态的转变。在这项研究中，pi利用这种转变提供的局部信息来解决有关微观非均质性和宏观流变学之间联系的基本问题。互补的计算机模拟，建立在一个现有的平台上，再现颗粒凝胶流变学的许多方面，并通过实验结果提供信息。该研究还利用了边界应力显微镜，这是一种由pi开发的技术，可以测量剪切凝胶边界的局部应力，具有高空间和时间分辨率，直接将颗粒相互作用与中尺度应力非均质性联系起来。还将评估改变颗粒间摩擦的表面修饰对旋转动态-流变连接的影响。从这些测量中获得的见解可用于开发和验证计算模型，从而指导将微观和中尺度材料非均质性与其宏观力学联系起来的预测模型的开发。这项研究通过乔治城软物质综合与计量研究所维护的网络进行传播，包括半年一次的中大西洋软物质研讨会，并与乔治城新成立的地球共同环境与可持续发展研究所的一项倡议相联系，将可持续材料纳入其努力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。