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在各种材料中都发现，其应用从消费产品到生物制造和添加剂制造。尽管它们的重要性，但我们对微观结构与颗粒的动力学与凝胶的宏观机械性能之间的联系缺乏基本理解。结果，即使对粒子特性和浸入溶液的详细了解，我们也只能有限地预测基本特性（例如凝胶刚度和最终强度）。反过来，这限制了我们设计凝胶属性的能力。在这项工作中，我们将使用一套新颖的工具来揭示单个颗粒旋转的动力学，并使用此信息来确定粒子如何组装到支持力的网络中，并确定凝胶的刚度和强度。我们将使用这些见解来开发具有定义特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，以用于自我修复，刺激性反应性材料和3D打印的材料。 In addition, this project will support efforts to harness soft materials to address the profound challenges of sustainability by strengthening contacts between the soft material 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 deployment interaction, have provided a wealth of information and considerable insight into the connection between gel microstructure and mechanical properties.但是，这项工作的大部分受到无法直接评估凝胶状态的粒子尺度相互作用和动态的限制。该项目采用了含有异性核心的新型胶体颗粒，可以通过荧光显微镜精确地确定每个粒子的方向，并结合先进的仪器，从而允许简单的高速共聚焦成像和流变学。该项目利用了一个事实，即颗粒的方向动力学提供了对粒子间相互作用的非常敏感的测量，尤其是监测单个颗粒的旋转布朗运动的旋转运动表明，随着部署相互作用的强度增加，从旋转移动到被捕状态的过渡。在这项研究中，PI利用了此过渡提供的本地信息，以解决有关微观异质性与宏观流变学之间联系的基本问题。互补的计算机模拟，建立在现有的平台上，该平台再现了粒子凝胶流变学的许多方面，并通过实验结果为您提供了信息。该研究还探索了边界应力显微镜，这是通过PIS开发的一种技术，可以测量具有高空间和临时分辨率的剪切凝胶边界的局部应力，以将粒子相互作用与中尺度应力异质性直接连接起来。也将评估改变颗粒摩擦对旋转动力学连接的表面修饰的影响。这些测量结果的见解用于开发和验证计算模型，这反过来指导了将微观和中尺度材料异质性与宏观机械师联系起来的预测模型的发展。这项研究是通过乔治敦软件综合和计量学研究所维护的网络来分解的，包括半年度中大西洋软物质研讨会，并连接到将可持续材料整合到乔治敦新成立的地球环境和可持续性的努力中的努力的计划，该奖项是通过Internotient for Internotional的宣传来反映了NSF的宣称，并以DEEM为基础，并以此为由。优点和更广泛的影响审查标准。