Interfacial Phenomena Near Phase Transitions

该项目将研究发生体相变或表面相变时发生的各种表面过程。其中一个主题包括极化原子力显微镜和微观干涉测量，研究表面上液滴的形状和线张力，从纳米到许多微米的尺度，在湿润转变附近。这些数据将揭示表面相互作用、表面非均质性和温度对这些液滴的影响。第二个主题是原子力显微镜和光谱椭偏研究临界薄膜内的临界有限尺寸效应，以确定这种薄膜内的临界波动力和成分分布。最后一个主题是在临界二元液体混合物的液-汽表面偶极子诱导的表面取向顺序的椭圆偏振研究，以检查偶极子相互作用如何影响这些界面的组成剖面和取向顺序。在有限和半无限系统中，液滴在表面上的线张力效应和表面临界现象的普遍方面都知之甚少。液滴线张力强烈影响液滴在表面上的成核和聚并，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尤为重要。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，并最终能够设计出具有理想分子长度尺度特征的表面。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来研究前沿知识。这项研究将使这些学生为学术、工业或政府事业做好准备。这项工作寻求对表面或体相变点附近的许多液体表面过程的物理起源的定量理解，其中，表面或体分别经历作为温度函数的结构变化。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。数据应该揭示这些现象是如何受到表面相互作用、表面非均质性、体和表面相变的影响的。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)许多制造过程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性能非常重要。同样，在食品、制药和石油工业中使用的许多超临界萃取过程中，大块相变附近的表面现象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，并最终能够设计出在分子长度尺度上具有理想特征的表面。参与这项研究的学生将获得物理和材料科学方面的全面培训，这将为他们在学术、工业或政府领域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.