Molecular Visualization: Spreading Kinematics and Dynamics

聚合物薄膜在固体表面的铺展具有重要的理论意义和技术意义。在过去的20年里，人们进行了大量的实验和理论研究，以了解流体在表面上的传播方式。这些都导致了对润湿的宏观理解；然而，其分子机制在很大程度上仍不清楚。因此，显然需要开发能够在扩散过程中对单个分子进行可视化的实验方法。建议开发一种基于AFM和荧光显微镜相结合的分子扩散监测的集成系统。还建议使用支化的聚合物分子作为模型系统，可以通过所选的技术进行可视化。该项目将解决四个基本问题。(I)限制在表面的聚合物链的构象和堆积是什么？(Ii)聚合物分子在两个维度上的扩散运动学是什么，它与前驱体膜前沿的运动是什么关系？(3)动力和耗散通道是什么，它们对润湿动力学的相对贡献是什么？(4)表面流动的分子模式及其与衬底表面结构的关系是什么？这项工作将促进对润湿分子机理的基本理解，也将为操纵分子结构以控制润湿动力学提供实用指导。该项目还将为研究生和本科生提供跨学科的研究培训，因为它结合了精细的聚合物化学和先进的实验技术。在北卡罗来纳大学教堂山举行的定期科学研讨会和暑期研究中，已经与当地高中建立了互动关系，这是一个具有更广泛影响的特殊领域。除了教育方面，该项目还将加强研究三角地区的合作，包括北卡罗来纳大学、北卡罗来纳州立大学和杜克大学。由于其创新的方法--通过可视化单个分子来研究材料属性--该项目将对该领域的材料科学和工程产生广泛影响。

Spreading of thin polymer films on solid surfaces is of both fundamental and technological interest. During the last 20 years, significant experimental and theoretical studies have been carried out to understand the way fluids spread on surfaces. These have led to a macroscopic understanding of wetting; however, the molecular mechanism remains largely unknown. Thus, there is an apparent need for the development of experimental methods that are capable of visualization of individual molecules during spreading. It is proposed to develop an integrated system for monitoring molecular spreading based on a combination of AFM and fluorescent microscopy. It is also proposed to use branched polymer molecules as model systems that can be visualized by the chosen techniques. Four fundamental questions will be addressed in the project. (i) What is the conformation and packing of polymer chains confined to the surface plane? (ii) What is the spreading kinematics of polymer molecules in two dimensions and its correlation with the motion of the leading edge of the precursor film? (iii) What are the driving forces and dissipation channels, and their relative contribution to the wetting kinetics? (iv) What is the molecular pattern of the surface flow and its correlation with the surface structure of the substrate? This work will advance the fundamental understanding of the molecular mechanism of wetting and will also provide practical guidelines for manipulation of the molecular architecture to control the wetting kinetics.The project will also provide interdisciplinary research training for graduate and undergraduate students, since it combines fine polymer chemistry and advanced experimental techniques. An exceptional area of broader impact stems from the already established interactions with local high schools in form of regular scientific seminars and summer research at the UNC-Chapel Hill. In addition to the educational aspects, the project will reinforce collaborations in the Research Triangle Area including UNC, NCSU, and Duke University. Because of its innovative approach - investigation of material properties via visualization of individual molecules - this project will have broad impact on materials science and engineering in the area.