RUI: Viscosity Imaging and Chemical Reactions as Tools for Control of Fluid Instabilities

1335739本研究使用荧光探针成像反应流过程中的二维粘性场，以及纹影成像，以绘制流动不稳定性如何依赖于流体动力流动和化学反应的相对速率。建议的研究包括：(1)发展分子探针荧光成像技术，用于原位监测Hele-Shaw细胞中具有良好特性的可混溶的牛顿甘油-水体系的粘度；(2)将该技术扩展到测量阶跃聚合的化学反应流动体系的粘度场的时空演变；以及(3)研究反应速度与流体流动速度的相对作用。智力价值当高流动性的流体取代低流动性的流体时，就会发生称为指进的不稳定现象。如果两种流体的粘度相当，则流动性受密度差异的影响，并发生浮力驱动的对流。如果迁移率差异的来源是粘性，那么粘性指进可能发生在水平Hele-Shaw单元中。当不同粘度和密度的流体在重力场中聚集在一起时，结果取决于密度和粘度的稳定和不稳定作用的相对大小和迹象。这一建议侧重于在没有重力场的情况下，即在水平Hele-Shaw单元中的粘性指进(VF)。尽管粘性分布对VF的实验解释和理论模型具有重要意义，但粘性场在流动过程中仍未进行现场测量。因此，实际的粘度梯度必须假设或基于给定的模型进行内插。这项工作开发了一种使用粘度敏感荧光探针来解决这一问题的技术。在获得驱动VF的粘性场之后，人们希望控制该场和不稳定性。由于反应速率和反应产物的粘度都可以通过改变引发剂或催化剂的浓度或单体的官能度来控制，因此一组步进式聚合反应将被用作水平Hele-Shaw池中的模型体系。纹影成像将被用来产生一个相图，其结果是不稳定性与反应速率和流体动力流速的关系。粘度场的荧光探针成像将提供与粘度分布的理论模型相关的定量数据。更广泛的影响粘性指进已经得到了广泛的研究，部分原因是它在采油和在多孔介质中传播污染方面具有很大的影响。一方面有大量的实验研究，另一方面也有专注于计算粘性场时空演化的理论研究。然而，在实验和理论之间的定量比较中存在差距，这主要是由于局部粘度在空间和时间上的演化的定量测量的困难。这种对二维粘性场的现场定量监测能够调节相对反应和流体动力学时间尺度，这将广泛地影响多孔介质中流体动力不稳定性的场，并将导致控制不稳定性。此外，作为外展，物理与基础教育专业的学生将为中学生开展一系列光学和流体活动。这些活动将主要基于美国光学学会准备的光学发现工具包，但也将从流体动力学中提取更多的演示和活动。用品将保留在高需求学校(如西班牙裔城市特许学校)的一名中学理科教师手中，以使这名教师能够激发未来的学生。

1335739BuntonThis investigation uses fluorescent probe imaging of the two-dimensional viscosity field during reactive flow, as well as Schlieren imaging, to map how flow instabilities depend on the relative rates of hydrodynamic flow and chemical reactions. The proposed research includes: (1) development of molecular-probe fluorescence imaging technique for in situ monitoring of viscosity applied to a well-characterized miscible and Newtonian glycerol-water system in Hele-Shaw cells; (2) extension of this technique to measure the spatio-temporal evolution of the viscosity field for a chemically-reactive flow system of step-growth polymerization; and (3) investigation of the relative roles of rate of reaction to hydrodynamic flow rate. Intellectual Merit When a high-mobility fluid displaces a fluid of lower mobility, the instability known as fingering occurs. If the two fluids are of comparable viscosity, then the mobility is dominated by density differences and buoyancy-driven convection occurs. If the source of the mobility difference is viscosity, then viscous fingering can occur in a horizontal Hele-Shaw cell. When fluids of differing viscosities and densities are brought together in a gravity field, then the outcome depends on the relative sizes and signs of the stabilizing and destabilizing effects of density and viscosity. This proposal focuses on viscous fingering(VF) in the absence of a gravity field, i.e., in a horizontal Hele-Shaw cell. Despite the central importance of the viscosity profile to experimental interpretation and theoretical models of VF, the viscosity field has yet to be measured in situ during flow. Hence, the actual viscosity gradient must be assumed or interpolated based on a given model. This work develops a technique addressing this issue using a viscosity-sensitive fluorescent probe. After gaining the viscosity field driving VF, one desires to control the field and the instability. A set of step-growth polymerization reactions will be used as model systems in horizontal Hele-Shaw cells because both rate of reactivity and viscosity of the reaction product can be controlled by varying the concentration of the initiator or catalyst or the functionality of the monomers. Schlieren imaging will be used to produce a phase diagram of resultant instability versus rate of reaction and hydrodynamic flow rate. Fluorescent-probe imaging of the viscosity field will provide quantitative data that will be related to theoretical models of the viscosity profile. Broader Impacts Viscous fingering has been studied extensively in part due to its high impact in oil recovery and in pollution spreading in porous media. A large body of literature exists on experimental studies on one hand and on theoretical investigations that focus on computing the spatio-temporal evolution of viscosity fields. A gap exists however in quantitative comparisons between experiments and theory mainly due to the difficulty of quantitative measurements of the evolution in space and time of the local viscosity. This quantitative in-situ monitoring of 2D viscosity field enabling the tuning of the relative reaction and hydrodynamic time scales will broadly impact the field of hydrodynamic instabilities in porous media and will lead to controlling the instability. Additionally, as an outreach, Physics and Elementary Education students will implement a set of optics and fluids activities for middle school students. These activities will be primarily based on the Optics Discovery Kits prepared by the Optical Society of America but with additional demonstrations and activities drawn from fluid dynamics. Supplies will remain with a middle school science teacher in high-need school (such as an Hispanic urban charter school) to empower this teacher to excite future students.