POWRE: Rheology and Microstructure of Dilute Surfactant Systems in Complex Flows

表面活性剂或表面活性剂几乎渗透到我们日常生活的方方面面。生物功能、保健产品、清洁材料、油漆和许多其他产品和工艺都依赖于这些分子的独特性质。许多这些溶液性质源于表面活性剂在溶液中聚集，形成无数具有不同性质的结构。控制聚合结构的能力要求对系统参数的影响有基本的了解。虽然这种理解存在于平衡状态，但由外力（如流动）引起的结构变化并没有得到很好的研究。流量是一个相关变量，因为大多数基于表面活性剂的体系在应用、运输和加工过程中都受到流量的影响。线状胶束或一维聚集体在许多表面活性剂溶液中形成。在棒状（硬）胶束的稀溶液中加入低水平盐的情况下，观察到向剪切增稠状态的转变，并很好地表征了这种转变。在宏观和结构层面上对剪切引起的过渡都有定性的认识，而且这种认识正在变得更加定量。大多数研究集中在简单剪切场和Couette流变学上。除剪切外，流场的影响还没有被研究过，但要完全理解这一现象，需要这些类型的研究提供的信息。在本研究中，旨在同时探索更复杂流场中的宏观流动行为和微观结构变化。初始推力将涉及不均匀剪切流。然后，该研究将扩展到随着延伸水平的增加而增加的流场，以开始了解强流的影响。长期目标包括在宏观和微观结构水平上对拉长流动的研究。这项研究的结果将为这些胶束溶液的基于结构的本构方程的发展提供必要的信息，验证这些流体在特定工程应用（如减阻）中的潜力，并回答关于剪切诱导转变的性质的具体问题，这些问题不能单独用剪切来解释。

Surfactants, or surface active agents, pervade almost every aspect of our daily lives. Biological functions, healthcare products, cleaning materials, paints and many other products and processes rely on the unique properties of these molecules. Many of these solution properties arise from the fact that surfactants aggregate in solution, forming a myriad of structures with different properties. The ability to control aggregate structure requires a fundamental knowledge of the influence of system parameters. Although this understanding exists for equilibrium situations, the changes in structure caused by external forces, such as flow, are not well studied. Flow is a pertinent variable as most surfactant-based systems are subject to flow in application, transport and processing. Thread-like micelles, or one-dimensional aggregates, form in a number of surfactant solutions. In the case of dilute solutions of rod-like (stiff) micelles with low levels of added salt, a transition to a shear-thickened state has been observed and fairly well characterized. A qualitative understanding of the shear-induced transition exists both at a macroscopic and structural level and this understanding is becoming more quantitative. Most studies have focused on simple shear fields and Couette rheometry. The influence of flow fields other than shear has not been studied, yet information from these types of studies are required for a complete understanding of the phenomenon. In this proposed research, the intent if to simultaneously probe macroscopic flow behavior and microstructural changes in more complex flow fields. Initial thrusts will involve inhomogeneous shear flow. The study will then extend to flow fields with increasing levels of elongation to begin to understand the influence of strong flows. Long term goals include the study of elongational flows, both at the macroscopic and microstructural levels. Results from this research will provide information necessary for the development of struct ure based constitutive equations for these micellar solutions, verify the potential of these fluids n specific engineering applications (such as drag reduction) and answer specific questions about the nature of the shear-induced transition which cannot be elucidated with shear alone.