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

本研究使用荧光探针成像的二维粘度场在反应流动，以及纹影成像，以绘制流动的不稳定性是如何依赖于流体动力流动和化学反应的相对速率。拟开展的研究包括：(1)开发用于原位监测黏度的分子探针荧光成像技术，应用于Hele-Shaw细胞中表征良好的混相牛顿甘油-水体系；(2)将该技术扩展到测量阶梯生长聚合的化学反应流动体系的粘度场的时空演变；(3)反应速率与水动力流量的相对关系研究。当高迁移率流体取代低迁移率流体时，就会发生指指不稳定性。如果两种流体的粘度相当，则流动性由密度差决定，并发生浮力驱动的对流。如果迁移率差异的来源是粘度，那么在水平的Hele-Shaw细胞中就会发生粘指现象。当不同粘度和密度的流体在重力场中聚集在一起时，其结果取决于密度和粘度稳定和不稳定效应的相对大小和迹象。这一建议侧重于粘性指法（VF）在没有重力场，即，在一个水平Hele-Shaw细胞。尽管粘度剖面对VF的实验解释和理论模型至关重要，但在流动过程中粘度场尚未进行原位测量。因此，实际的粘度梯度必须根据给定的模型来假设或插值。这项工作开发了一种使用粘度敏感荧光探针解决这一问题的技术。在获得驱动VF的黏度场后，人们希望控制该场和不稳定性。由于反应产物的反应速率和粘度可以通过改变引发剂或催化剂的浓度或单体的功能来控制，因此一组阶梯生长聚合反应将被用作水平Hele-Shaw细胞中的模型系统。纹影成像将用于生成不稳定性与反应速率和流体动力流速的相图。粘度场的荧光探针成像将提供定量数据，这将与粘度剖面的理论模型有关。由于粘指法对石油采收率和多孔介质污染扩散的影响很大，因此粘指法得到了广泛的研究。大量的文献一方面是关于实验研究，另一方面是关于计算黏度场时空演化的理论研究。然而，实验和理论之间的定量比较存在差距，这主要是由于难以定量测量局部粘度在空间和时间上的演变。通过对二维黏度场的定量原位监测，可以调整相对反应和水动力时间尺度，这将对多孔介质的水动力不稳定场产生广泛的影响，并有助于控制不稳定。此外，作为拓展，物理和基础教育的学生将为中学生实施一套光学和流体活动。这些活动将主要以美国光学学会准备的光学发现工具包为基础，但将增加流体动力学方面的演示和活动。在高需求学校（如西班牙裔城市特许学校）的一名中学科学教师将继续获得物资，以使这名教师能够激励未来的学生。

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.