Using confocal rheometry to investigate shear thickening suspensions

胶体悬浮液的粘度可以随着剪切速率的不同而变化数量级。这种非牛顿行为源于悬浮粒子的排列及其相互作用。虽然数值模拟和散射实验揭示了许多关于局部和平均悬浮结构的信息，但介观长度尺度上的粒子动力学仍然知之甚少，而非牛顿行为被认为起源于介观尺度。这项研究计划将继续开发结合快速共聚焦显微镜和同步流变学测量的技术，以确定悬浮液介观结构的变化如何改变悬浮液的粘度。目前的工作将集中在与剪切增稠悬浮相关的三个主题上。首先，我们将确定在不同大小的空隙中，水团的大小分布如何改变剪切增厚。这项任务将通过直接可视化不同剪切速率下的氢团簇并研究它们在限制下的行为来实现。其次，我们将确定颗粒形状如何增强剪切增稠。二聚体和立方体粒子将被用来研究形状各向异性如何影响增厚。最后，我们将调查在高体积分数时增稠的机制是否起源于流体动力学，或者是否如许多小组所说的那样，在高体积分数时摩擦接触力起作用。这些共聚焦流变学技术为确定非牛顿悬浮液的微观动力学提供了一种新的方法。最终，该项目开展的研究将使剪切增稠液的设计成为可能。由于剪切增稠材料在工业应用中发挥着重要作用，这类研究将产生重大影响。这些流体可以在各种材料中找到，从涂料到浆体，甚至是建议用于顶压的剪切稠化钻井液。程序(如用于控制井喷的程序？)Macondo油井)。它们在加工和包装过程中的非牛顿行为使它们的处理变得非常复杂。因此，设计合适的防止或加速悬浮液流变性快速变化的流动环境和流体的目标将对常见的工业实践产生重大影响。将开展一些教育和推广活动。PI参与创建关于科学中紧急现象的基于性能的演示文稿。除这项活动外，国际和平协会还将继续每半年举办一次纽约复杂问题讲习班。这些会议旨在促进来自锡拉丘兹、康奈尔、RIT、通用电气、柯达、康宁等机构和该地区工业实验室的软物质和统计物理研究人员之间的互动。这些工作坊将是一个极好的机会，将研究生和博士后介绍给当地的学术和工业研究社区。

1232666PI: CohenThe viscosity of colloidal suspensions can vary by orders of magnitude with shear rate. Such non-Newtonian behavior arises from the arrangement of suspended particles and their mutual interactions. Although numerical simulations and scattering experiments revealed much about the local and average suspension structures, particle dynamics at mesoscopic length scales, where non-Newtonian behaviors are believed to originate, are still poorly understood. This research program will continue to develop techniques that combine fast confocal microscopy with simultaneous rheological measurements to determine how changes in suspension mesoscopic structure alter the suspension viscosity. The current work will focus on three themes associated with shear thickening suspensions. First, we will determine how hydrocluster size distribution alters shear thickening in different size gaps. This task will be achieved by directly visualizing hydroclusters at various shear rates and investigating their behavior under confinement. Second we will determine how particle shape enhances shear thickening. Dimer and cubic particles will be used to investigate how shape anisotropy affects thickening. Finally we will investigate whether mechanisms for thickening at high volume fractions are hydrodynamic in origin or if, as many groups claim, at high volume fractions frictional contact forces come into play. These confocal rheometry techniques illustrate a new approach for determining the microscopic dynamics of non-Newtonian suspensions. Ultimately, research carried out in this project will enable design of shear thickening fluids. Such studies will have substantial ramifications due to the important role that shear thickening materials play in industrial applications. These fluids can be found in materials ranging from paints, to pastes, and even shear thickening drilling mud proposed for ?top kill? procedures (such as those used to control the ?blowout? of the Macondo well). Their handling is substantially complicated by their non-Newtonian behavior during processing and packaging. Thus, the goal of designing flow environments and fluids that when appropriate prevent or precipitate rapid changes in suspension rheology will have substantial impact on common industrial practices.A number of Education and outreach activities will be carried out. The PI is involved in creating performance based presentations on emergent phenomena in science. In addition to this activity, the PI will continue to organize the semiannual New York Complex Matter Workshops. These meetings are aimed at stimulating interaction among soft matter and statistical physics researchers from Syracuse, Cornell, RIT, General Electric, Kodak, Corning and other institutions and industrial labs in the area. The workshops will serve as an excellent opportunity for introducing graduate students and postdocs to the local academic and industrial research community.