Rheology of complex fluids in micro/nanoscale passages

许多天然或工业流体，如食品和饮料、药品、涂料和洗涤剂，都含有乳状液或泡沫形式的液体。在大多数情况下，分散的液体在第二个不相容的液体或气体中形成液滴，形成一个界面，在界面上薄膜分离紧密接触的液滴。分散的液滴通过这种薄膜相互作用，因此测量这些形成的界面的物理化学性质是很重要的。粘度是一种基本的流体性质，定义为流体系统中应力和变形之间的关系。对于乳液和泡沫，液-液或液-气层界面的粘度可能与整体粘度有很大不同，并主导分散液滴相互作用的方式。这就是为什么界面粘度主要与分散体、乳液和泡沫的长期稳定性有关。准确测量界面粘度极具挑战性，通常通过添加可能影响界面化学的示踪颗粒等间接方法来完成。此外，大规模测量技术缺乏足够的灵敏度来产生可靠的测量。*本研究计划致力于开发一种结合全内反射显微镜(TIRM)和数值模型的纳米流体平台，可在不添加任何示踪剂颗粒的情况下直接测量液体薄膜的粘度。这种含有特征尺寸小至10 nm的平行通道的纳米流体系统将被用来在长度尺度上评估与实际分散系统中的薄膜相当的界面粘度。多通道几何结构可以产生大量数据，以增加我们测量的统计可靠性，同时为所有通道保持相同的实验条件。毛细管力将被用来诱导纳米通道中的流动。结合涂布方法，研究润湿性对液膜表观粘度的影响。TIRM显微镜将用于直接测量毛细管在流道中运动时液体的动态接触角。将开发一个理论模型来捕捉通道中牛顿和非牛顿液体的毛细流动。一般模型将被纳入我们的实验结果，以计算薄膜粘度。*拟议计划的预期贡献可以显著提高我们对复杂液体系统的了解，并导致开发出根据预期结果控制乳液和分散体稳定性的技术。这些技术在我所在小组调查的领域中有许多应用，包括油包水乳状液的稳定性、在现场提取沥青时在多孔介质中的混合和传质，以及非水沥青提取。

Many natural or industrial fluids such as foods and beverages, pharmaceuticals, coatings, and detergents involve liquids in forms of emulsions or foams. In most cases, a dispersed liquid forms droplets in a second immiscible liquid or gas creating an interface where a thin film separates close-contact droplets. The dispersed droplets interact with each other through this thin film so it is importance to measure the physicochemical properties of these formed interfaces. Viscosity is a fundamental fluid property and is defined as the relation between stress and deformation in fluid systems. For emulsions and foams, the viscosity at the interface of liquid-liquid or liquid-gas layer can be very different from the bulk viscosity and dominates how the dispersed droplets interact with each other. That is why interfacial viscosity has been primarily linked to the long-term stability of dispersion, emulsions, and foams. Exact measurement of viscosity of interfaces is extremely challenging and is usually done by indirect methods such as addition of tracing particles that could affect the chemistry of the interfaces. Moreover, large scale measurement techniques lack the sufficient sensitivity to produce reliable measurements. ******This research program focuses on developing a nanofluidic platform coupled with total internal reflection microscopy (TIRM) as well as numerical models to directly measure the viscosity of thin liquid films without addition of any tracer particles. The nanofluidic system containing parallel channels with characteristic sizes as small as 10 nm will be fabricated to evaluate interfacial viscosity at length scales comparable to the thin film in real dispersion systems. Many-channel geometry can produce large amount of data to increase the statistical reliability of our measurement while maintaining the same experimental conditions for all the channels. Capillary forces will be used to induce the flow in nanochannels. Incorporating coating methods, the effects of wettability on apparent viscosity of the thin liquid film will be studied. TIRM microscopy will be employed to directly measure dynamic contact angle of liquids during capillary motion in the channels. A theoretical model will be developed to capture the capillary flow of both Newtonian and non-Newtonian liquids in channels. The general model will be incorporated in our experimental results to calculate thin film viscosity. ******The expected contributions from the proposed program can significantly advance our knowledge of complex liquid systems and result in developing techniques to control the stability of emulsions and dispersions according to the desired outcome. These techniques have many applications in the areas under investigation in my group, including water-in-oil emulsion stability, mixing and mass transfer in porous media during in-situ bitumen extraction, and non-aqueous bitumen extraction.**