Thin Liquid Films - Structure and Stability

本研究的目的是从实验和理论两方面考察亚微米薄液膜的多层微结构或分层现象，其流体表面由表面活性剂布朗粒子胶束稳定；进一步探索其作为探针在胶体分散体中有序诱导长程结构力的应用。这项持续研究的一个独特之处在于使用其新仪器对具有流体界面的弯曲膜进行表面力平衡，以研究多层微结构对膜厚度稳定性的影响。表面力平衡将与微分干涉显微镜一起用于研究对称泡沫和乳液膜，以及不对称膜，例如接近的小油滴和空气-水表面或水滴和空气-油表面之间的膜。使用来自阿贡国家实验室先进光子源的同步辐射的x射线衍射将用于直接观察具有流体表面的薄液体膜内的固有层内结构。利用微分和普通微干涉方法进行实验，以获得薄膜半月板的局部平均曲率和膜/半月板接触角，从而获得由于薄膜内部胶束结构的存在而导致的薄膜多余能量和分离压力。本文提出利用共聚焦扫描激光荧光显微镜和低角度透射光衍射技术研究液体薄膜与半月板之间区域，即楔形薄膜内部的胶束/颗粒结构。实验将与我们的蒙特卡罗和分子动力学模拟进行比较。将评估影响薄膜结构和稳定性的重要工艺因素，如有效胶束/颗粒体积分数、薄膜尺寸及其厚度、颗粒尺寸、形状和多分散性。要研究的系统将包括球形和非球形胶束，混合胶束（如阴离子和非离子胶束溶液的混合物），蛋白质，和不同电荷的胶体颗粒，如乳胶和二氧化硅，以及水胶体，如胶质和淀粉。这项关于液体薄膜现象的研究旨在了解表面诱导的结构/耗竭力在稳定或破坏泡沫、乳液和胶体分散体中的作用。

ABSTRACT CTS9423584 Wasan, D.T. Illinois Institute of Technology The objective of this research is to examine, both experimentally and theoretically, the phenomenon of multilayered microstructuring or stratification in sub-micron thin liquid films with fluid surfaces stabilized by surfactant micelles of Brownian particles; further to explore its use as a probe for investigating order inducing long-range structural forces in colloidal dispersions. A unique feature of this continuing study lies in the use of its newly instrumented surface force balance for curved films with fluid interfaces for investigating the influence of multilayered microstructuring on film thickness stability. Surface force balance will be used in conjunction with differential interference microscopy to study symmetric foam and emulsion films as well as asymmetric films such as those between approaching small oil droplets and an air-water surface or water droplets and an air-oil surface. X-ray diffraction using synchrotron radiation from the advanced Photon Source at Argonne National Laboratory will be used to directly observe the intrinsic, in-layer structure within thin liquid films with fluid surfaces. Experiments using differential and common microinterferometric methods will be performed to obtain the local mean curvature of the film meniscus and the film/meniscus contact angles and, thereby, the film excess energy and the disjoining pressure attributable to the presence of micellar structure inside the film. It is proposed to investigate the micellar/particle structure in the region between the thin liquid film and the meniscus, i.e., inside the wedged film by using Confocal Scanning Laser Fluorescence Microscopy as well as low-angle, transmitted light diffraction technique. The experiments will be compared with our Monte Carlo and Molecular Dynamics simulations. Important technological factors affecting the film structure and stability, such as effective micelle/particle volume fraction, film size and i ts thickness, particle size, shape and polydiserpisity, will be evaluated. Systems to be investigated will include both spherical and non-spherical micelles, mixed micelles (such as mixtures of anionic and nonionic micellar solution), proteins, and differentially charged colloidal particles such as latexes and silica, and hydrocolloids such as gums and starches. This study on thin liquid film phenomena is aimed at understanding the role of surface-induced structural/depletion forces in stabilizing or destabilizing foams, emulsions, and collodical dispersions.