Collaborative Research: Active and Nonlinear Microrheology

建议编号：0730292/0730270研究人员：Furst，Eric M./Squires，Todd M.机构：特拉华大学/加州大学圣巴巴拉分校合作研究：主动和非线性微观流变学在过去十年中见证了被动微观流变学技术的发展，其中胶体示踪剂颗粒的布朗运动与周围材料的线性粘弹性性质有关。微观流变学测量的显著好处包括：只需要微升样品，提供更宽的频率范围，以及能够探测空间流变性变化。因此，工业界对适应和采用微观流变学方法表现出了极大的兴趣。长期以来，人们一直认识到，加工复杂流体的大多数工业流程都涉及到与线性流变学的重大偏离。然而，被动微观流变学本质上不能测量非线性流变性。在这里，目标是开发第一个微观流变技术来测量非线性材料的性质。这项合作工作将发展实验技术(使用激光镊子和高速共聚焦显微镜来测量力和胶体探头穿过材料时的非平衡结构)以及理解和解释结果的理论基础。目前，所有的理论和实验都集中在直接的探针-熔池相互作用上，这种相互作用在宏观流变学中不起作用，在被动微观流变学中表现为伪影。要将非线性微观流变学建立为材料表征的一般技术，必须理解和解决这些问题，必须开发和验证解释结果的有充分依据的方法。在为这些问题建立了理论和实验框架后，原理研究人员预计将使用更复杂的技术(例如，涉及多个和各向异性探头)来更可靠地测量非线性整体流变学以及正常应力测量。其学术价值在于提出了发展和改进非线性微观流变学的第一项技术，从而建立了一个全新的流变学领域。更广泛的影响是，微观流变学的发展有望在将生产扩大到工业规模之前测量非线性特性。通过合作和博士行业实习，与宝洁的互动将加快这些方法的转移。此外，PIS将利用现有的NSF资助的推广计划，将本科生、未被充分代表的少数民族以及高中生和教师纳入他们的研究努力，在这个经济和技术上重要的领域提供教育机会。

PROPOSAL NO.: 0730292/0730270PRINCIPAL INVESTIGATOR: Furst, Eric M./Squires, Todd M. INSTITUTION: University of Delaware/University of California-Santa Barbara COLLABORATIVE RESEARCH: ACTIVE AND NONLINEAR MICRORHEOLOGY The past decade has seen the development of techniques in passive microrheology, where the Brownian motion of colloidal tracer particles is related to the linear viscoelastic properties of the surrounding material. Significantly benefits from microrheological measurements include: requiring mere microliters of sample, providing an extended range of frequencies, and having the ability to probe spatial rheological variation. For this reason, industry has shown significant interest in adapting and adopting microrheological approaches. It has long been appreciated that most industrial flows for processing complex fluids involve significant departures from linear rheology. However, passive microrheology is by nature incapable of measuring nonlinear rheological properties. Here, the goal is to develop the first microrheological techniques to measure nonlinear material properties. The collaborative effort will develop both experimental techniques (the use of laser tweezers and high speed confocal microscopy to measure the force and non-equilibrium structure as a colloidal probe is driven through a material) as well as the theoretical basis to understand and interpret the results. Currently, all theory and experiments have focused exclusively on direct probe-bath interactions, which play no role in macro-rheology and appear as artifacts in passive microrheology. To establish nonlinear microrheology as a general technique for material characterization, these issues must be understood and addressed, and well-founded methods for interpreting the results must be developed and validated. Having established the theoretical and experimental framework for these issues, the Principle Investigators anticipate using more sophisticated techniques (e.g. involving multiple and anisotropic probes) for more faithful measurements of nonlinear bulk rheology as well as normal stress measurements. The intellectual merit is in proposing to develop and refine the first techniques for nonlinear microrheology, thus establishing an entirely new area of rheology. Broader impact is the development of microrheology promises to measure nonlinear properties before scaling up production to industrial scale. Interactions with Procter and Gamble will speed transfer of these methods, both through collaboration and PhD industrial internships. Additionally, the PIs will leverage existing NSF-funded outreach programs to incorporate undergraduates, under-represented minorities and high-school students and teachers into their research efforts, providing educational opportunities in this economically and technically important field.