Career Program: A Theoretical and Experimental Investigation of Novel Interfacial Instabilities in Thin Spreading Films

9624776 Troian随着技术向加工和仪器小型化的推进，人们对流体薄膜在受限几何结构中的行为又产生了新的兴趣。人们特别关注的问题是，超小型几何形状的传输如何导致系统的行为方式与其散装时的行为方式明显不同。在化学工程中，这一重点已直接转化为对界面处液体的结构和动力学的研究。即使是简单的牛顿液体，最近也发现了与表面张力、表面张力梯度、蒸发和范德华力之间的相互作用有关的新的输运行为——这些力已经研究了一个多世纪，但它们的耦合会导致非常薄的薄膜中有趣的和意想不到的不稳定性。本研究的总体目标是对一种液体在高表面张力的支撑液体表面上的扩散动力学有一个完整和基本的理解，特别关注稳定性问题。第一个项目涉及水动力指进不稳定性的表征，这种不稳定性发生在表面活性剂溶液沿着潮湿的支撑物扩散的过程中。考虑到这个简单的实验室标记的含义，以区分表面活性剂溶液提供稳定的均匀覆盖从那些产生不稳定，树枝状和不均匀覆盖。第二种不稳定性涉及与蒸发效应耦合的马兰戈尼应力。在自发孔洞成核和生长后，挥发性烃液膜从大块水支撑体后退，沿着加厚的后退边缘，一种新的指进不稳定性沿展向发展。了解如何防止这种不稳定性可能会带来涉及Marangoni应力的碳氢化合物分离新技术。这个为期四年的实验和理论项目将对这些不稳定性进行表征，这些不稳定性可以显著影响系统中的输运行为，从肺流中的表面活性剂输运到光学微器件中使用的有机薄膜的制造，再到薄膜中碳氢化合物混合物的分离。这两种不稳定性及其特征图案形成发生在覆盖在液体载体表面的液体薄膜的前进或后退前沿。挑战在于从液体力学的角度充分表征流动，更重要的是利用这些知识来开发实用方案，以增强传输特性并减少薄膜中不均匀的表面覆盖。对这些方案提出了建议。＊＊＊

9624776 Troian In parallel with the technological push toward miniaturization of processing and instrumentation, there has developed renewed interest in the behavior of thin fluid films in confined geometries. Particular attention is being drawn to the question of how transport in ultrasmall geometries can cause a system to behave in ways significantly different than its behavior in bulk. In chemical engineering this focus has translated directly into investigations of the structure and dynamics of liquids at interfaces. Even for the case of simple Newtonian liquids, novel transport behavior has been recently uncovered related to the interplay between surface tension, surface tension gradients, evaporation, and Van derWaals forces - forces which have been studied for over a century but whose coupling can lead to interesting and unexpected instabilities in very thin films. The general objective of this research is to develop a complete and fundamental understanding of the spreading kinetics of one liquid on the surface of a supporting liquid higher surface tension with particular focus on issues of stability. The first project involves the characterization of a hydrodynamic fingering instability which occurs during the advance of spreading surfactant solutions along a moist support. Given the implications of this simple laboratory marker to differentiate surfactant solutions providing stable homogeneous coverage from those yielding unstable, dendritic, and inhomogeneous coverage. The second instability involves Marangoni stresses coupled to evaporative effects. A novel fingering instability develops spanwise along the thickened receding edge of a volatile hydrocarbon liquid film receding from a bulk water support after spontaneous hole nucleation and growth. Understanding how to prevent such an instability can lead to a new technique for hydrocarbon separation involving Marangoni stresses. The four year experimental and theoretical program will characterize these instabilities wh ich can significantly affect transport behavior in system ranging from surfactant transport in pulmonary flow, to the fabrication of organic films used in optical microdevices, to the separation of hydrocarbon mixtures in the films. These two types of instabilities and their characteristics pattern formations develop at the advancing or receding front of a thin liquid film coating the surface of a liquid support. The challenge is to fully characterize the flows from a liquid mechanical point of view and more importantly to use this knowledge to develop practical schemes with which to enhance transport properties and reduce inhomogeneous surface coverage in thin spreading films. Suggestions for such schemes are described. ***