Probing and directing colloidal migration by sculpting chemical micro-environments

CBET 1438779许多具有工业和生物重要性的材料由悬浮在液体中的小胶体颗粒组成。 粒子非常小，它们会响应周围环境施加在它们身上的各种力而运动。 本计画将研究扩散电泳，即胶体粒子因应溶解溶质（如液体中的作为盐）浓度变化而产生的运动。 将开发一种基于微流体的装置，该装置可以在液体中产生和保持溶质浓度梯度。 然后，胶体颗粒在液体中的运动将被直接观察到，并与浓度梯度的方向和大小相关联。将检查各种颗粒和不同种类的溶质浓度梯度。 虽然已经有理论发展来解释扩散电泳，但很少有实验可用于测试这些理论。 研究结果将帮助科学家和工程师制定和处理用于各种行业的胶体悬浮液。 该项目将为研究生和本科生提供研究培训机会，并将让小学生参与工程原理和应用的演示。虽然胶体扩散电泳在工业和涂层工艺中起着核心作用，并且在平衡或反应表面周围很常见，但它比其他迁移现象如电泳更少被理解。 在宏观系统中建立强大的，稳定的，无对流梯度的挑战混淆了直接测量的扩散电泳迁移率。 该项目将使用一种微流体装置，该装置具有集成到其通道壁中的水凝胶微窗口膜。 水凝胶窗口对于溶质和溶剂扩散是可渗透的。 通过窗口的扩散将允许在设备的选定通道上建立和维持空间和时间溶质梯度。 一个干涉技术将被用来测量溶质浓度，和胶体扩散电泳流动性将通过直接观察粒子运动来测量。 该设备还将配备用于测量相同胶体的电泳迁移率。 新的电泳现象将被识别和开发用于结构软材料的直接组装。

CBET 1438779Many materials of industrial and biological importance consist of small colloidal particles suspended in a liquid. The particles are so small that they move in response to various forces exerted on them by their surroundings. This project will study diffusiophoresis, which is the motion of colloidal particles in response to concentration variations of a dissolved solute such as salt in the liquid. A microfluidic-based device will be developed that can create and maintain solute concentration gradients in a liquid. Then, the motion of colloidal particles in the liquid will be observed directly and correlated with the direction and magnitude of the concentration gradient. A variety of particles and different kinds of solute concentration gradients will be examined. Although there have been theories developed to explain diffusiophoresis, there are few experiments available to test those theories. The results will help scientists and engineers formulate and process colloidal suspensions that are used in a variety of industries. The project will provide research training opportunities for graduate and undergraduate students and will engage elementary school students in demonstrations of engineering principles and applications.Although colloidal diffusiophoresis plays a central role in industrial and coating processes, and is common around equilibrating or reacting surfaces, it is less well understood than other migration phenomena such as electrophoresis. Direct measurements of diffusiophoretic mobilities are confounded by the challenges of establishing strong, stable, convection-free gradients in macroscopic systems. This project will use a microfluidic device that has hydrogel micro-window membranes integrated into its channel walls. The hydrogel windows are permeable to solute and solvent diffusion. Diffusion through the windows will allow spatial and temporal solute gradients to be established and maintained across selected channels of the device. An interferometric technique will be used to measure solute concentration, and colloidal diffusiophoretic mobility will be measured by direct observation of particle motion. The device will also be equipped to measure electrophoretic mobility of the same colloid. New phoretic phenomena will be identified and exploited for direct assembly of structure soft materials.