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，都以乳液或泡沫的形式存在。在大多数情况下，分散的液体在第二种不混溶的液体或气体中形成液滴，形成一个界面，在该界面上，薄膜将紧密接触的液滴分开。分散的液滴通过薄膜相互作用，因此测量这些形成的界面的物理化学性质具有重要意义。粘度是流体的一种基本性质，被定义为流体系统中应力与变形之间的关系。对于乳液和泡沫，液-液或液-气层界面处的粘度可能与体粘度有很大不同，并且决定了分散的液滴如何相互作用。这就是为什么界面粘度主要与分散剂、乳液和泡沫的长期稳定性有关。界面粘度的精确测量是极具挑战性的，通常通过间接方法来完成，例如添加可能影响界面化学性质的示踪颗粒。此外，大规模测量技术缺乏足够的灵敏度，无法产生可靠的测量结果。******这个研究项目的重点是开发一个纳米流体平台，结合全内反射显微镜（TIRM）和数值模型，直接测量薄液体薄膜的粘度，而不添加任何示踪颗粒。该纳米流体系统包含特征尺寸小至10nm的平行通道，将用于在与真实分散系统中的薄膜相当的长度尺度上评估界面粘度。多通道几何可以产生大量数据，以提高我们测量的统计可靠性，同时保持所有通道相同的实验条件。毛细管力将被用来诱导纳米通道中的流动。结合涂覆方法，研究润湿性对液体薄膜表观粘度的影响。在毛细管在通道中运动时，将使用TIRM显微镜直接测量液体的动态接触角。将建立一个理论模型来捕捉牛顿流体和非牛顿流体在通道中的毛细管流动。一般模型将被纳入我们的实验结果来计算薄膜粘度。******该计划的预期贡献可以显著提高我们对复杂液体系统的认识，并根据期望的结果开发控制乳液和分散体稳定性的技术。这些技术在我小组正在研究的领域有许多应用，包括油包水乳液稳定性、原位沥青提取过程中多孔介质的混合和传质，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.**