Using confocal rheometry to investigate shear thickening suspensions

1232666PI：Cohen胶体悬浮液的粘度可随剪切速率变化几个数量级。这种非牛顿行为源于悬浮颗粒的排列及其相互作用。虽然数值模拟和散射实验揭示了很多关于局部和平均悬浮结构，在介观长度尺度上的粒子动力学，其中非牛顿行为被认为是起源，仍然知之甚少。这项研究计划将继续开发技术，结合联合收割机快速共聚焦显微镜与同步流变测量，以确定如何在悬浮液介观结构的变化改变悬浮液粘度。目前的工作将集中在三个主题与剪切增稠悬浮液。首先，我们将确定水团簇的大小分布如何改变不同大小的间隙中的剪切增稠。这一任务将通过直接可视化在各种剪切速率下的水团簇和调查其约束下的行为来实现。其次，我们将确定颗粒形状如何增强剪切增稠。二聚体和立方粒子将用于研究形状各向异性如何影响增厚。最后，我们将研究是否在高体积分数增厚的机制是流体动力学的起源，或者如果，许多团体声称，在高体积分数摩擦接触力发挥作用。这些共焦流变技术说明了一种新的方法来确定非牛顿悬浮液的微观动力学。最终，在该项目中进行的研究将能够设计剪切增稠流体。由于剪切增稠材料在工业应用中的重要作用，这些研究将产生实质性的后果。这些流体可以在从油漆到糊状物的材料中找到，甚至可以在建议用于钻井的剪切增稠钻井泥浆中找到。顶级杀戮程序（如用于控制？井喷？马孔多井（Macondo Well）在加工和包装过程中，它们的非牛顿行为使它们的处理相当复杂。因此，设计流动环境和流体的目标，在适当的时候防止或促进悬浮液流变学的快速变化，将对常见的工业实践产生重大影响。PI参与创建基于表现的演示文稿，介绍科学中出现的现象。除了这一活动外，PI将继续组织半年一次的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、康宁和该地区其他机构和工业实验室的软物质和统计物理研究人员之间的互动。这些研讨会将成为向当地学术和工业研究界介绍研究生和博士后的绝佳机会。

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.