Surfactant Flow and Foam Stability

摘要：0086751M。DenninUniversity California@Irvine这项研究是利用光学和流变学技术相结合的方法研究朗缪尔单分子膜的流动行为。它包括两组实验：研究水相中多价离子对朗缪尔单分子膜流动行为的影响；以及研究混合表面活性剂体系的流动行为。重点放在直接影响泡沫和乳液稳定性的体系及其流动特性上。拉格缪尔单分子膜本质上是二维的，由限制在空气-水界面的两亲性分子组成。本工作中使用的朗缪尔槽由两个垂直定向的同心圆柱体组成。内筒是固定的，外筒是自由转动的。水的顶面是自由的，单层放置在这个表面上。因此，单分子层模拟标准含水泡沫中的气液界面。内筒由两部分组成。水相中有一个静止的圆柱体，还有一个正好与水面接触的扭转摆。直流粘度的测量是通过旋转外筒并用扭摆测量内筒上的应力来实现的。交流粘度是通过固定外筒并摆动扭转摆来测量的。通过用浏览器角度显微镜直接观察速度分布和磁区动力学，获得了关于单层流动特性的附加信息。由于对其液体凝聚(LC)相的阐明，人们对迟滞矿物层的流变学重新产生了兴趣。LC相是三维近晶液晶的二维类似物。它们具有六方有序，在分子相对于表面倾斜的相中，倾斜方位显示出取向顺序。由于LC相在朗缪尔单分子膜中普遍存在，因此了解其流变性与涉及界面表面活性剂单分子层流动的一系列过程具有相关性。最近的工作重点是脂肪酸单分子膜，因为它们的相行为已经被彻底研究，并观察到了广泛的有趣的流动现象。尽管如此，即使是纯脂肪酸单分子膜的流动行为也没有完全被理解。这里的工作建议将这些测量扩展到脂肪酸盐(在水亚相中存在离子的脂肪酸单层)和混合脂肪酸/酯体系。我们将讨论一些基本问题。平衡相的结构和单分子膜的粘弹性质之间有什么联系？带电单层和多价离子之间的相互作用如何影响单层的流动特性？子相中的流动如何影响单分子层的结构，这对主体流动有什么影响？选择这两个系统的动机是它们在泡沫稳定性方面的作用。溶液中离子的存在经常被发现是稳定的泡沫。另一方面，脂肪酸盐也可以用来减少泡沫。这里提出的对脂肪酸盐的研究将有助于阐明电解液作为泡沫稳定剂和不稳定物的双重作用。它甚至可能导致一种作为时间函数来控制泡沫稳定性的方法。脂肪酸/酯混合物通常用作泡沫稳定剂。此外，表面粘度和泡沫稳定性之间也存在相关性。然而，目前对稳定机制还没有根本的了解。这可能是粘度和稳定性之间的简单关系，也可能涉及LC相的非牛顿性质。混合物的使用使人们可以在固定的温度和压力下改变体系的相和相应的流动行为。将对亚相流与单层之间的相互作用进行初步研究。

ABSTRACTCTS_0086751M. DenninUniversity California @ IrvineThis research is a study of the flow behavior of Langmuir monolayers using a combination of optical and rheological techniques. It consists of two sets of experiments: a study of the effects of the multivalent ions in the water subphase on the flow behavior of Langmuir monolayers; and a study of the flow behavior of mixed surfactant systems. The focus is on systems and their flow properties that directly impact foam and emulsion stability.Lagmuir monolayers are intrinsically two-dimensional and consist of amphiphilic molecules that are confined to the air-water interface. The Langmuir trough used in this work consists of two concentric cylinders that are oriented vertically. The inner cylinder is fixed and the outer cylinder is free to rotate. The top surface of the water is free, and the monolayer is placed on this surface. As such, the monolayer models the gas-liquid interfaces in a standard aqueous foam. The inner cylinder consists of two parts. A stationary cylinder in the water subphase, and a torsion pendulum that just makes contact with the water surface. The dc viscosity is measured by rotating the outer cylinder and measuring the stress on the inner cylinder with the torsion pendulum. The ac viscosity is measured by holding the outer cylinder fixed and oscillating the torsion pendulum. Additional information about the flow properties of the monolayer is obtained by direct observation of velocity profiles and domain dynamics with a Browser angle microscope.There has been a renewed interest in the theology of Languor minelayers, in part, due to the elucidation of their liquid condensed (LC) phases. The LC phases are two-dimensional analogs of three-dimensional smectic liquid crystals. They posses hexatic order, and in phases where the molecules are tilted with respect to the surface, the tilt azimuth exhibits orientational order. Because LC phases are ubiquitous in Langmuir monolayers, understanding their reheology has relevance to a range of processes that involve surfactant monolayer flow at interfaces. The focus of recent work has been on fatty acid monolayers, as their phase behavior has been thoroughly studied, and a wide range of interesting flow phenomena has been observed. Despite this, even the flow behavior of the pure fatty acid monolayers is not completely understood. The work here proposes to extend these measurements to fatty acid salts (fatty acid monolayers in the presence of ions in the water subphase) and mixed fatty acid/ester system. A number of fundamental question will be addressed. What is the connection between the structure of the equilibrium phases and the viscoelastic properties of the monolayer? How do interactions between charged monolayers and multivalent ions affect the flow properties of the monolayer? How do flows in the subphase impact the structure of the monolayer, and what effect does this have on the bulk flow?The motivation for choosing these two systems is their role in foam stability. The presence of ions in solution is often found to stabilized foams. On the other hand, fatty acid salts can also be used to decrease foaming. The study of fatty-acid salts proposed here will help elucidate this dual role of electrolytes as foam stabilizers and destabilizes. It may even result in a method for controlling foam stability as a function of time. Fatty acid/ester mixtures are often used as foam stabilizers. Also, there is a correlation between surface viscosity and foam stability. However, there is no fundamental understanding of the stabilizing mechanism. It may be a simple relationship between viscosity and stability, or it may involve non-Newtonian properties of the LC phases. The use of mixtures allows one to alter the phase of the system and the corresponding flow behavior, for a fixed temperature and pressure. Preliminary studies the interaction between subphase flows and the monolayer will be made.