Tailoring emulsions of complex fluids for precise wetting and coalescence rates

乳液是两种不混溶液体的混合物，其形式为一种液体悬浮在另一种液体中的液滴。尽管在日常生活和工业中无处不在，但由于缺乏将其组成，加工和结构与其性质联系起来的基本关系，乳液仍主要通过组合方法配制。该项目旨在弥补文献中两个重要的乳液相关现象的这一空白：润湿，即乳液滴在表面上的扩散，以及聚结，即两滴合并成一个更大的滴。 在许多应用中，调节聚结和润湿速率以实现所需的产品特性或特定功能至关重要。 但是，虽然有几项研究解释润湿和聚结的热力学方面，这些现象发生的速率的调查是稀疏的。 基于乳液的产品形成了一个价值数十亿美元的产业，因此，对这两个关键现象的基本理解的任何改进都可以为该行业带来实质性的利益。 我们的聚结和润湿研究的重点将是一类称为复杂流体的流体。 这些流体是Jekyll和Hyde流体，并且可以表现得像固体或液体，这取决于如何对它们施加应力。尽管大多数工业乳液是由复杂的流体制成的，但对这些材料的聚结和润湿性了解最少。 在这项工作中，我们将集中在三个复杂的流体：聚合物熔体的聚合物共混物，表面活性剂的解决方案，广泛用于特定的铺展性能和稳定的乳液配方对聚结，和屈服应力流体，用于稳定乳液对重力。 为了解开这些复杂流体的聚结或润湿的管理机制和时间尺度，我们将采用Cantidos微量移液器装置（CMD）结合称为反射干涉对比显微镜（RICM）的光学技术。 CMD将使我们能够测量液滴与固体-流体或流体-流体界面之间的力，精确到纳牛顿的几分之一。同时，我们将使用RICM测量低至纳米的薄膜接触轮廓，并尽可能使用低温扫描电子显微镜补充数据。 从这项工作的知识和工具将使我们能够量化的速率聚结和表面润湿的复杂流体组成的乳液，促进乳液设计与预选润湿和聚结时间，并允许从目前的经验设计范式的过渡。在加拿大有几个以乳液为基础的行业，每一个都是至少数百万美元的行业。 当HQP在我们的实验室中接受最先进的方法培训后加入劳动力队伍时，他们将为加拿大工业提供巨大的竞争优势。

An emulsion is a mixture of two immiscible liquids in the form of drops of one liquid suspended in the other. In spite of being ubiquitous in everyday life and in the industry, emulsions are still being formulated largely by combinatorial methods, due to a lack of the fundamental relationships that connect their composition, processing and structure to their properties. This project aims to remedy this gap in the literature for two important emulsion-related phenomena: wetting, which is the spreading of an emulsion drop on a surface, and coalescence, which is the union of two drops into one larger drop. In many applications, it is critical to tune the coalescence and wetting rates to achieve the desired product properties or specific functions. But while there are several studies explaining thermodynamic aspects of wetting and coalescence, investigations of the rates at which these phenomena occur are sparse. Emulsion-based products form a billion dollar industry, hence any improvement in the fundamental understanding with respect to these two key phenomena can lead to substantial benefits to the industry. The emphasis of our coalescence and wetting studies will be on a class of fluids called complex fluids. These fluids are Jekyll and Hyde fluids, and can behave like solids or liquids depending on how stresses are imposed on them. Coalescence and wetting are least understood for these materials, in spite of the fact that most industrial emulsions are made out of complex fluids. In this work, we will focus on three complex fluids: polymer melts in the context of polymer blends, surfactant solutions which are used extensively in emulsion formulations for specific spreading properties and for stability against coalescence, and yield stress fluids which are used to stabilize emulsions against gravity. To unravel the governing mechanisms and time scales of coalescence or wetting for these complex fluids, we will employ the Cantilevered Micropipette Device (CMD) in conjunction with an optical technique called Reflection Interference Contrast Microscopy (RICM). The CMD will allow us to measure the force between a drop and a solid-fluid or fluid-fluid interface down to a fraction of a nanoNewton. Simultaneously, we will measure the film contact profile down to a nanometer using RICM, and supplement the data with cryo-Scanning Electron Microscopy wherever possible. The knowledge and tools from this work will allow us to quantify the rates of coalescence and surface wetting in emulsions composed of complex fluids, facilitating emulsion design with preselected wetting and coalescence times and allow a transition away from the current empirical design paradigm. There are several emulsion-based industries in Canada, and each of these is, at least, a multimillion dollar industry. When HQP trained in our lab in state-of-the-art methods join the workforce, they will provide Canadian industry a huge competitive edge.