A New Stress Bearing Mechanism in Non-Newtonian Fluids

Deegan 0932600 PI发现了两种现象，持续空洞和负流，这两种现象共同表明剪切增稠复合流体具有振动激活的应力承载机制。一个持续的空洞可以保持一个与重力平行的稳定的自由面。负流是与平均施加的应力相反的流。实验室实验和建模将揭示这些现象的起源，PI认为这些现象具有相同的物理起源。PI将研究这两个类别并与Ronald Larson合作开发基于这些结果的流变学模型，并与Rich Kerswell合作开发和验证基于流动测量和流变学模型的自由面模型。实验将在振动测试平台上进行，并使用粒子图像测速仪在定制的剪切单元中进行。这种流变学将用商用应力控制流变仪进行表征。将使用粒子跟踪、光散射显微镜和共聚焦显微镜来表征流体结构。流场测量与流变学模型相结合，将有助于建立和验证持续孔洞和负流的流体动力学模型。结构表征将揭示微观结构与流变行为之间的联系。这项研究的结果将对复杂流体群落，特别是剪切带、剪切增稠和堵塞群落具有广泛的意义。它还将引起许多行业的兴趣--从塑料到化妆品再到制药--在这些行业中，通常使用非牛顿流体。这项研究有可能揭示复杂流体的基本机制，这种机制可能与正常应力或拉伸粘度一样重要。少年派的教育项目建立在他的YouTube上关于持续洞穴的视频的基础上，这段视频已经被观看了超过250万次，并在旧金山探索馆的一个开发的最后阶段的展览上。此外，PI将在复杂系统研究跨学科中心开发和教授一门新的非线性科学实验室课程。在PI实验室参加暑期实习的本科生将受益于对科学职业机会和研究生入学竞争力的认识的提高。

Deegan 0932600The PI discovered two phenomena, persistent holes and negative flows, which together suggest that shear-thickening complex fluids possess a vibration-activated stress-bearing mechanism. A persistent hole can maintain a stable free surface oriented parallel to gravity. Negative flows are flows that are opposite to the mean applied stress. Laboratory experiments and modeling will reveal the origin of these phenomena which the PI believes have the same physical origin. The PI will study the two classes and develop a rheological model based on these results in collaboration with Ronald Larson and develop and validate a free surface model based the flow measurements and the rheological model in collaboration with Rich Kerswell. The experiments will be conducted on a vibrating test platform and in a custom built shear cell using Particle Image Velocimetry. The rheology will be characterized with a commercial stress-controlled rheometer. The fluid structure will be characterized using particle tracking, light scattering microscopy, and confocal microscopy. The flow field measurements combined with the rheological model will help build and validate a hydrodynamic model of persistent holes and negative flows. The structural characterization will reveal the link between the microscopic structure and the rheological behavior. The results of this study will be of interest broadly to complex fluids community and specifically to the shear banding, shear thickening, and jamming communities. It will also be of interest to the many industries - from plastics to cosmetics to pharmaceuticals - in which non-Newtonian fluids are commonly used. This study has the potential to reveal a fundamental mechanism in complex fluids which may be as significant as normal stress or extensional viscosity. The PI's educational program builds on his YouTube video of persistent holes, that has been viewed over 2.5 million times and on an exhibit in the final stages of development at the San Francisco Exploratorium. In addition, the PI will develop and teach a new laboratory course on nonlinear science in the interdisciplinary Center for the Study of Complex Systems. Undergraduates participating in summer internships in the PI's lab will benefit from an increased awareness of career opportunities in science and competitiveness for graduate school entry.