Foam Structure and Rheology

榴莲本项目旨在阐明液体泡沫中气泡的随机填充结构的性质，以及这种结构的后果，它们的动力学，以及它们的时间演变，对宏观流变行为。这包括两个主要领域的努力：(a)光通过多次散射在泡沫中的传播以及利用这种普遍现象作为结构探针，以及(b)演化和剪切引起的结构重排对线性剪切流变学和时间演化的影响。特别感兴趣的是确定是否存在线性状态，结构重排是否可以发挥相当于热波动的作用并因此被赋予一个“温度”，以及流动是否可以影响时间演变。流变学测量将通过商用设备和定制的Couette-cell完成，后者允许通过多种光散射技术同时测量气泡填充结构和动力学。由此获得的基本理解可以为更复杂的系统提供一个框架，在这些系统中，密集的随机堆积和不可逆的结构重排决定了宏观行为，如致密乳液、胶体悬浮液和颗粒状介质。液体泡沫是由大量的气泡非常紧密地聚集在少量的液体中组成的，就像我们日常生活中所熟悉的那样。提出的实验旨在帮助实现对这些材料的重要特性的基本理解，即它们的稳定性和流动行为，在它们的微观结构和组成方面。由于光被气泡界面强烈散射，因此限制了对气泡填充结构的视觉观察，因此对气泡表面的气泡知之甚少。然而，我们最近开发了新的实验技术，利用多重光散射的优势，首次揭示了包装结构及其行为的细节。通过使用这些技术获得的基本理解可以使发泡液体配方、发泡技术和消泡剂的合理设计成为可能。这将使目前通过试错法处理泡沫的各种行业受益：食品、化妆品、洗涤剂、采矿、石油、纸浆和造纸、油漆和涂料、纺织、皮革、聚合物以及废物和水修复。* * *

w:\awards\awards96\*.doc 9623567 Durian This project seeks to elucidate the nature of the random packing structures of bubbles in liquid-based foams and the consequences of such structures, their dynamics, and their time evolution, for the macroscopic rheological behavior. This included efforts in two main areas: (a) The propagation of light through foams by multiple-scattering and the use of this generic phenomenon as a structural probe, and (b) The influence of evolution and shear-induced structural rearrangements on linear shear rheology and time evolution. Special interest is in determining if a linear regime exists, if structural rearrangements can play a role equivalent to thermal fluctuations and hence be assigned a "temperature", and if flow can affect time evolution. Rheology measurements will be accomplished with a commercial device and also with a custom Couette-cell which allows simultaneous access for measurement of the bubble-packing structure and dynamics by multiple light scattering techniques. The fundamental understanding thus achieved may provide a framework for more complex systems where dense random packing and irreversible structural rearrangements dictate macroscopic behavior, such as dense emulsions, colloidal suspensions, and granular media. %%% Liquid-based foams consist of a large number of gas bubbles very closely packed together in a small amount of liquid, as familiar from everyday life. The proposed experiments are designed to help achieve a fundamental understanding of the important properties of these materials, namely their stability and flow behavior, in terms of their microscopic structure and composition. Little is yet known due to the fact that light is strongly scattered by the bubble interfaces, thus restricting visual observation of the bubble-packing structure to the surface bubbles. However, we have re cently developed new experimental techniques which take advantage of multiple light scattering and which reveal for the first time details of the packing structure and its behavior. The fundamental understanding achieved through use of these techniques may enable rational design of foaming-liquid formulations, foaming techniques, and anti-foaming agents. This could benefit diverse industries where foams are currently dealt with by trial-and-error: food, cosmetic, detergent, mining, petroleum, pulp & paper, paint & coating, textile, leather, polymer, and waste and water remediation. ***