Decoupling dynamics from the rheology of surface-anisotropic colloids

胶体由分散在液体中的微米级颗粒组成。由于颗粒的尺寸很小，它们的运动会受到与流体分子碰撞的影响。胶体存在于广泛的工程产品中，如药品、乳制品和油浆。尽管它们无处不在，但传统的工程方法并没有考虑到这些颗粒具有粗糙表面的事实。当粒子负载较低时，这种与完美、理想化、平滑球体的形状差异不会造成问题。然而，当这些粒子堆积得更紧密时，实验数据和理论之间会发现很大的不一致。这些偏差阻碍了含有粗糙颗粒的悬浮液加工流动条件的工程设计，这些颗粒由于固体-固体接触而产生摩擦相互作用。本项目的目标是研究胶体表面粗糙度对各种流动现象的影响。悬浮液的动力学、微观结构和性能之间的联系将使用安装在共焦显微镜上的特殊构造的设备来实现。这项工作的结果将导致在其产品中使用粗糙或不规则表面的胶体颗粒的工业设计规则。此外，从该项目获得的知识将用于利用社交媒体进行STEM教育的外联活动。将向公众提供一系列Reddit互动外联活动，以有趣和易于理解的方式展示关于材料流动和质地的复杂科学概念。该奖项旨在激发美国年轻一代的想象力，并引导他们走向当今科学和工程事业中的奇迹和发现。该奖项旨在了解表面各向异性得到很好控制的模型聚合物胶体的微观动力学。中心假设是具有不同表面特征的胶体的平移和旋转扩散在高颗粒负载下独立地解耦。动力学的解耦导致了线性和非线性流变学与当前理论预测的显著偏离。这项工作将对颗粒扩散如何影响浓缩悬浮液的线性和非线性流变性产生新的物理理解。在这种情况下，流体悬浮液的机械性能变得越来越透明。这些现象背后的基本原理仍未得到很好的理解，特别是当粒子之间进行固体-固体接触时。这项工作将通过成像光滑和粗糙的胶体在快速共焦流变仪中的流动来研究微观机制，该装置旨在同时捕捉剪切流动中的旋转动力学。具有短程流体动力相互作用的布朗动力学模拟将被纳入，以支持动力学的实验观察和与玻璃流变学的联系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Colloids consist of micron-sized particles dispersed in a fluid. Due to the small size of the particles, their motion is affected by collisions with the fluid molecules. Colloids are found in a broad range of engineered products, such as pharmaceuticals, dairy foods, and oil slurries. Despite their ubiquity, traditional engineering approaches have not accounted for the fact that these particles possess rough surfaces. This difference in shape from a perfect, idealized, smooth sphere does not cause problems when the particle loading is low. However, when such particles are packed more closely, large disagreements between experimental data and theories are found. These deviations have hampered the engineering of processing flow conditions for suspensions containing rough particles that generate frictional interactions due to solid-solid contact. The goal of this project is to investigate the effect of colloidal surface roughness on a variety of flow phenomena. Connections between dynamics, microstructure, and properties of the suspensions will be made using a specially constructed apparatus mounted on a confocal microscope. The results from this work will lead to design rules for industry for the use of colloid particles with rough or irregular surfaces in their products. In addition, knowledge gained from this project will be used in outreach activities that utilize social media for STEM education. A series of Reddit interactive outreach activities that present complex scientific concepts about the flow and texture of materials in an interesting and digestible way will be made available to the general public. The goal is to capture the imagination of the nation's younger generation and to guide them towards the wonders and discoveries present in today's science and engineering careers.This award aims to understand the microscopic dynamics of model polymeric colloids with well-controlled surface anisotropy. The central hypothesis is that the translational and rotational diffusion of colloids with various surface features becomes independently decoupled at high particle loadings. The decoupling of dynamics leads to significant departures in the linear and nonlinear rheology from current theoretical predictions. This work will generate new physical understanding of how particle diffusivity affects the linear and nonlinear rheology of concentrated suspensions. In this regime, fluid suspensions become increasingly glassy in their mechanical properties. The fundamental rationale behind these phenomena is still not well understood, particularly when particles make solid-solid contacts with one another. This work will investigate the microscopic mechanisms by imaging smooth and rough colloids flowing within a fast confocal rheometer setup designed to concurrently capture rotational dynamics during shear flow. Brownian Dynamics simulations with short-range hydrodynamic interactions will be incorporated to support experimental observations of dynamics and connections to glassy rheology.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.