Collaborative Research: Active and Nonlinear Microrheology

提案编号：0730292/0730270 首席研究员：Furst, Eric M./Squires, Todd M. 机构：特拉华大学/加州大学圣塔芭芭拉分校 合作研究：主动和非线性微流变学 过去十年见证了被动微流变学技术的发展，其中布朗运动胶体示踪颗粒与周围材料的线性粘弹性特性有关。微观流变测量的显着优势包括：仅需要微升样品、提供更广泛的频率范围以及能够探测空间流变变化。因此，工业界对采用微流变学方法表现出了浓厚的兴趣。人们早就认识到，大多数用于处理复杂流体的工业流程都与线性流变学有很大的偏差。然而，被动微流变学本质上无法测量非线性流变特性。这里的目标是开发第一种微流变技术来测量非线性材料特性。这项合作将开发实验技术（使用激光镊子和高速共焦显微镜来测量胶体探针穿过材料时的力和非平衡结构）以及理解和解释结果的理论基础。目前，所有理论和实验都只关注直接探针与浴的相互作用，这在宏观流变学中不起任何作用，并且在被动微观流变学中表现为伪影。为了将非线性微流变学建立为材料表征的通用技术，必须理解和解决这些问题，并且必须开发和验证有根据的方法来解释结果。在为这些问题建立了理论和实验框架后，原理研究人员预计使用更复杂的技术（例如涉及多个各向异性探针）来更准确地测量非线性体流变学以及法向应力测量。其智力价值在于提出开发和完善非线性微流变学的第一个技术，从而建立一个全新的流变学领域。更广泛的影响是微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。与宝洁公司的互动将通过合作和博士工业实习加速这些方法的转移。此外，PI 将利用现有的 NSF 资助的推广计划，将本科生、代表性不足的少数族裔以及高中生和教师纳入他们的研究工作，从而在这个经济和技术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.