Interfacial Phenomena Near Phase Transitions

这个项目将调查各种表面过程中发生的无论是散装或表面相变发生。 一个主题包括一个偏振原子力显微镜和显微干涉仪的形状和表面上的液滴的线张力的研究，从纳米尺度到许多微米，在附近的润湿过渡。 这些数据应该揭示表面相互作用，表面不均匀性，和温度对这种液滴的影响。 第二个主题是一个原子力显微镜和椭圆偏振光谱研究的临界有限尺寸的影响，在薄的临界膜，以确定在这种膜的临界波动力和成分分布。 最后一个主题是偶极诱导的表面取向顺序在临界二元液体混合物的液体-蒸气表面的椭圆偏振研究，以研究偶极相互作用如何影响在这样的接口的组合物配置文件和取向顺序。液滴在表面上的线张力效应以及有限和半无限系统中的表面临界现象的普遍性方面都知之甚少。液滴线张力强烈影响液滴在表面上的成核和聚结，而表面临界现象在食品、制药和石油工业中使用的许多超临界萃取过程中特别重要。对表面现象的更好理解将导致对表面相关过程的更好控制，并最终导致在分子长度尺度上设计具有所需特性的表面的能力。这些项目将为研究生提供优秀的培训，使用创新的表面技术在知识的前沿主题。这项研究将使这些学生为学术、工业或政府职业做好准备。%这项工作旨在定量了解的物理起源的一些液体表面过程的附近的表面或体相转变点，其中，分别是表面或散装经历的结构变化作为温度的函数。 创新的光学和力显微镜技术将用于研究表面分子的取向，表面上液滴的形貌和相关能量，以及薄膜内液体混合物的结构。 这些数据应该揭示这些现象是如何受到表面相互作用、表面不均匀性以及体相和表面相转变的影响。 了解液滴形貌及其如何受到表面相互作用和表面相变的影响，对于控制（i）许多制造工艺中使用的表面涂层的均匀性和（ii）织物和纤维的润湿或非润湿特性非常重要。类似地，本体相变附近的表面现象在食品、制药和石油工业中使用的许多超临界萃取过程中起着极其重要的作用。对这些过程的更好理解将导致对表面相关过程的更好控制，并最终导致在分子长度尺度上设计具有期望特性的表面的能力。参与这项研究的学生将获得物理学和材料科学的全面培训，这将为他们在学术，工业或政府竞技场的职业生涯做好准备。

This project will investigate a variety of surface processes that occur when either a bulk or a surface phase transition takes place. One topic consists of a polarization atomic force microscopy and microscopic interferometry study of the shape and line tension of droplets on surfaces, from scales of nanometers through to many microns, in the vicinity of a wetting transition. These data should reveal the influence of surface interactions, surface heterogeneities, and temperature on such droplets. A second topic is an atomic force microscopy and spectroscopic ellipsometry study of critical finite-size effects within thin critical films to ascertain the critical fluctuation force and composition profile within such films. The final topic is an ellipsometry study of dipole-induced surface orientational order at the liquid-vapor surface of critical binary liquid mixtures to examine how dipole interactions influence the composition profile and orientational order at such interfaces. Line tension effects of droplets on surfaces and the universal aspects of surface critical phenomena, in both finite and semi-infinite systems, are poorly understood. Droplet line tensions strongly influence the nucleation and coalescence of droplets on surfaces, while, surface critical phenomena are particularly important in many supercritical extraction processes used in the food, pharmaceutical, and petroleum industries. An improved understanding of surface phenomena will lead to better control of surface related processes and ultimately to the ability to design surfaces possessing desirable characteristics on the molecular length scale. These projects will provide graduate students with excellent training using innovative surface techniques on topics at the forefronts of knowledge. This research will prepare these students well for academic, industrial, or government careers.%%%This work seeks a quantitative understanding of the physical origins of a number of liquid surface processes in the vicinity of either a surface or a bulk phase transition point where, respectively, either the surface or the bulk undergo a structural change as a function of temperature. Innovative optical and force microscopy techniques will be used to study the orientation of molecules at surfaces, the topography and associated energies of droplets on surfaces, and the structure of liquid mixtures within thin films. The data should reveal and how these phenomena are influence by surface interactions, surface heterogeneities, and bulk and surface phase transitions. An understanding of droplet topography and how it is influenced by surface interactions and the presence of a surface phase transition is important in governing (i) the uniformity of surface coatings used in many manufacturing processes and (ii) the wetting or non-wetting properties of fabrics and fibers. Similarly, surface phenomena in the vicinity of a bulk phase transition plays an extremely important role in many supercritical extraction processes used in the food, pharmaceutical, and petroleum industries. An improved understanding of these processes will lead to a better control of surface related processes and ultimately to the ability to design surfaces possessing desirable characteristics on the molecular length scale. Students involved in this research will gain a comprehensive training in physics and material science which will prepare them well for careers in the academic, industrial, or government arena.