Particle Motion in Colloidal Dispersions: Microrheology and Microdiffusivity

胶体分散体中的粒子运动：微流变学和微扩散性

• 批准号: 0931418
• 负责人: John Brady
• 金额: $ 30万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0931418&HistoricalAwards=false
• 关键词: Particle; Motion; Colloidal; Dispersions; Microrheology

0931418 Brady Intellectual Merit: The increased demand for knowledge of small scale behavior has made microrheology a key step in the understanding of biological systems and the design and use of advanced materials and nano scale devices. Most microrheological work to date has focused on linear viscoelastic properties, by correlating the random thermally driven displacements of tracers to the complex modulus through a generalized Stokes Einstein relation, a process which is well understood but which is limited in its scope to equilibrium systems. But many systems of practical interest are driven out of equilibrium and display (indeed, rely upon) nonlinear behaviors. Recently a body of work has emerged focusing on this active, nonlinear microrheology. In such a system, tracer particles undergo displacements due not only to random thermal fluctuations, but also due to the application of an external force applied directly to the tracer. The dispersion is driven out of equilibrium, and as with macrorheology, dynamic responses such as viscosity can be measured. Since the tracer probes the material at its own (micro)scale, much smaller samples are required compared to macrorheology, and localized heterogeneity can be explored. Recent experiments confirm the theory; but in both theory and experiment, the focus thus far has remained on the mean response of the material the viscosity and little focus has been devoted to particle uctuations. Just as the shear flow in macrorheology enhances particle diffusion, an analogous `force induced' diffusivity arises due to the single particle forcing of active microrheology. This diffusive motion is fundamental to the motion of an active microscale particle important both for scientific and technology considerations. The proposed research extends the theory of active microrheology to the force induced diffusive motion of individual particles, as well as normal microstress differences. This work will combine theoretical and computational studies, focusing on colloidal systems because they offer very well characterized materials, allowing for comparisons to macroscale measurements. But the impact of this research extends beyond colloids, as the theoretical foundation and general conclusions are extendable to many complex materials, especially biomaterials. Other issues such as the effect of tracer size on the `continuum approximation', and hydrodynamic interactions between pairs of moving particles leading to structure formation, will be addressed. This work will expose new material capabilities and ultimately provide a validation of microrheology as a sound technique, critical for its continued application and future growth.Broader Impact: Motion control for active microscale particles is a major focus in many fields from biophysics to alternative energy to nanomedicine and it begins with understanding the fluctuations in particle motion. Since this research provides the theoretical foundation for new experimental techniques that have widespread application in science and technology, its impact is both very broad and deep. This research will develop PhD students into experts in colloid physics, rheology, and computational methods, who will become leaders in industry and academia. To aid in the education of future scientists and engineers, a microrheology section for the Caltech chemical engineering laboratory will be created. To disseminate the research widely, a publicly accessible website showcasing research results will accompany publication in technical journals.

0931418 Brady知识分子：对小规模行为知识的需求增加使微流行病学成为理解生物系统以及高级材料和纳米尺度设备的设计和使用的关键步骤。迄今为止，大多数微型流变学工作都集中在线性粘弹性上，通过将示踪剂的随机热驱动位移与复合模量通过广义的stokes Einstein关系相关联，这一过程被充分理解，但在其范围中限制在平衡系统中。但是，许多实践感兴趣的系统都被驱逐出均衡和显示（实际上是依赖）非线性行为。最近，出现了一系列工作，专注于这种活跃的非线性微流变学。在这样的系统中，示踪剂颗粒不仅由于随机的热波动而经历位移，而且还由于直接应用于示踪剂的外力。分散剂是从平衡中驱动的，并且与大型学一样，可以测量诸如粘度之类的动态响应。由于示踪剂自行（微型）尺度探测材料，因此与大型学相比，需要较小的样品，并且可以探索局部异质性。最近的实验证实了这一理论。但是在理论和实验中，到目前为止的重点一直放在材料的平均响应上，粘度和焦点很少用于粒子的含量。 正如大型学中的剪切流量增强了粒子的扩散一样，由于主动微流变性的单个粒子强迫，产生了类似的“力诱导”扩散率。 这种扩展运动对于对科学和技术考虑重要的主动微观粒子运动的运动至关重要。 提出的研究将主动微流变学的理论扩展到了力引起的单个颗粒的扩散运动以及正常的显微肌肉差异。 这项工作将结合理论和计算研究，重点关注胶体系统，因为它们提供了非常有特征的材料，从而可以与宏观测量值进行比较。 但是，这项研究的影响超出了胶体的范围，因为理论基础和一般结论可扩展到许多复杂的材料，尤其是生物材料。 其他问题，例如示踪剂大小对“连续近似”的影响，以及导致结构形成的运动粒子对之间的水动力相互作用。这项工作将揭示新的材料能力，并最终提供微流变学作为一种声音技术的验证，对于其持续的应用和未来的增长至关重要。BROADER的影响：主动微观颗粒的运动控制是从生物物理学到替代能量到纳米医学的许多领域的主要重点，它始于理解粒子运动的波动。由于这项研究为在科学技术中广泛应用的新实验技术提供了理论基础，因此其影响既广泛又深刻。 这项研究将把博士生发展为胶体物理，流变学和计算方法的专家，他们将成为工业和学术界的领导者。为了帮助对未来的科学家和工程师的教育，将创建一个Caltech化学工程实验室的微流变科。为了广泛传播研究，公开访问的网站展示研究结果将伴随在技术期刊上的出版物。