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。尽管它们的重要性，我们缺乏一个基本的理解之间的联系的微观结构和动力学的颗粒和宏观力学性能的凝胶。因此，我们只有有限的能力来预测基本性质，如凝胶刚度和极限强度，即使有详细的知识，颗粒的性质和溶剂，他们沉浸。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，我们将使用一套新的工具来揭示，第一次，单个粒子的旋转动力学，并使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来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和政策制定者之间的联系，支持利用软材料来应对可持续发展的深刻挑战。技术摘要：当微米级胶体颗粒通过短程吸引力相互作用时形成的凝胶的颗粒分辨研究，介导的耗尽相互作用，提供了丰富的信息和相当多的洞察力凝胶微观结构和机械性能之间的联系。然而，这项工作的大部分是有限的，无法直接评估颗粒尺度的相互作用和动力学的凝胶状态。该项目采用含有偏心核的新型胶体颗粒，该偏心核允许通过荧光显微镜精确确定每个颗粒的取向，并结合先进的仪器，允许同时进行高速共聚焦成像和流变学。该项目利用的事实是，粒子的取向动力学提供了一个非常敏感的测量粒子间的相互作用，特别是，监测旋转布朗运动的单个粒子揭示了从旋转移动的逮捕状态的过渡，作为耗尽相互作用的强度增加。在这项研究中，PI利用这种转变提供的本地信息来解决微观异质性和宏观流变学之间的联系的基本问题。互补的计算机模拟，建立在现有的平台上，再现了颗粒凝胶流变学的许多方面，通知和实验结果。该研究还利用了边界应力显微镜，这是PI开发的一种技术，能够以高空间和时间分辨率测量剪切凝胶边界处的局部应力，将颗粒相互作用与中尺度应力异质性直接联系起来。还将评估改变颗粒间摩擦的表面改性对旋转动力学-流变学连接的影响。从这些测量的见解被用来开发和验证计算模型，这反过来又指导预测模型的发展连接微观和介观尺度的材料异质性，其宏观力学。这项研究是通过乔治敦软物质合成和计量研究所维护的网络传播的，包括半年一次的大西洋中部软物质研讨会，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响审查标准。