Non-Newtonian Fluids in Squeeze Films

由于微流体学和纳米粒子科学与工程的重要性日益增加，流体在狭窄通道中的流动受到越来越多的关注。缩小到更小的长度尺度提出了一些有趣的问题，包括：固液界面的边界条件是什么？如何在狭窄的通道中增强流体的流动？复杂流体的流动如何受到约束进入薄膜的影响？在这里，我们建议用胶体探针显微镜来研究球体和平板之间的挤压膜中的流体流动来解决这些问题。该方法最近已成功地确定了简单液体固液界面的无滑移边界条件，为研究更复杂的流体做好了准备。这项工作的结果在两个领域有影响。首先，由于颗粒的广泛使用以及在膜、半导体晶圆等上存在颗粒污染，当小颗粒靠近板时作用在它们身上的力本身就很重要。其次，这些测量为研究流体边界条件和约束对流体流动的重要性等基本问题打开了一扇窗。建议使用力显微镜来测量胶体粒子接近平板时的力、速度和位移。微粒将浸入流体中。测量参数将与理论值进行比较，以验证理论。一阶理论将是简单液体在蠕变流动下的布伦纳润滑结果。通过与该理论的比较，我们可以确定有效滑移长度和有效粘度。测量将在各种非牛顿流体上进行，包括聚合物熔体，表面活性剂溶液，纳米颗粒分散体和稀薄气体。要解释这些测量结果，需要一些理论的发展。将尝试通过在界面处吸附低粘度流体或薄膜来增强流动。该建议还通过增加可访问的频率和剪切速率范围来改进胶体力测量。采用高速驱动装置可获得更高的剪切速率，而采用振荡驱动装置可获得更高的频率。这种振荡驱动可以同时测量小范围内的弹性和耗散响应。胶体探针显微镜的优点是在位移和力的实现非常高的分辨率。例如，胶体探针显微镜可以确定滑移长度只有几个纳米的不确定度。该计划的教育组成部分将是培养一名博士后研究员，一名研究生和一名本科生。

CBET-0828163DuckerThe flow of fluid in narrow channels is receiving increased attention because of the growing importance of both microfluidics and nanoparticle science and engineering. Reduction to smaller length scales raises interesting questions, including: what is the boundary condition at the solid-liquid interface? How can the flow of fluid be enhanced in narrow channels? How is the flow of complex fluids affected by confinement into a thin film? Here we propose to address these questions by using colloidal probe microscopy to study the flow of fluids in the squeeze film between a sphere and a plate. This method has recently been successful in confirming the no-slip boundary condition at the solid-liquid interface for simple liquids, and is now ready for the study of more complex fluids. The outcomes of this work have implications in two fields. First, the forces acting on small particles as they approach plates are important for in their own right because of the widespread use of particles and the presence of particle contamination on membranes, semiconductor wafers etc. Second, these measurements open a window on fundamental questions such as the fluid boundary conditions and the importance of confinement on fluid flow. The proposal is to use force microscopy to measure the force, velocity and displacement of a colloidal particle as it approaches the plate. The particle will be immersed in a fluid. The measured parameters will be compared to theoretical values to validate theories. The first order theory will be Brenner's lubrication result for simple liquids under creeping flow. Comparison to this theory allows us to determine the effective slip-length and the effective viscosity. Measurements will be made on a variety of non-Newtonian fluids, including polymer melts, surfactant solutions, nanoparticle dispersions, and rarefied gases. Some development of theory will be necessary to interpret these measurements. Attempts will be made to enhance flow through the adsorption of low viscosity fluids or films at the interface. The proposal is also to improve the colloidal force measurement by increasing the range of frequencies and shear rates that are accessible. Greater shear rates will be accessed by incorporating a high velocity drive, and greater frequencies will be accessed by development of an oscillatory drive. This oscillatory drive will enable the simultaneous measurement of elastic and dissipative responses over a small range of separations. The advantage of colloidal probe microscopy is the very high resolution in displacement and force that is achieved. For example, colloidal probe microscopy can determine the slip-length with only a few nanometers of uncertainty. The educational component of this proposal will be to train a post-doctoral researcher, a graduate student and undergraduate students.