Molecular Visualization: Spreading Kinematics and Dynamics

聚合物薄膜在固体表面上的铺展是一个基础性和技术性的问题。在过去的20年中，已经进行了重要的实验和理论研究，以了解流体在表面上的传播方式。这些都导致了宏观的理解润湿，然而，分子机制仍然在很大程度上未知。因此，显然需要开发能够在扩散期间可视化单个分子的实验方法。提出了一种基于原子力显微镜和荧光显微镜相结合的分子铺展监测集成系统。它还建议使用支化聚合物分子作为模型系统，可以通过所选择的技术可视化。该项目将解决四个基本问题。(i)什么是构象和包装的聚合物链限制在表面平面？(ii)聚合物分子在二维空间的扩散运动学是什么？它与前体膜前缘的运动有什么关系？(iii)什么是驱动力和耗散通道，以及它们对润湿动力学的相对贡献？(iv)表面流的分子模式是什么及其与基底表面结构的相关性？这项工作将推进对润湿分子机制的基本理解，并将为操纵分子结构以控制润湿动力学提供实用指南。该项目还将为研究生和本科生提供跨学科的研究培训，因为它结合了精细聚合物化学和先进的实验技术。一个具有更广泛影响的特殊领域源于已经建立的与当地高中的互动，其形式是在北卡罗来纳大学教堂山的定期科学研讨会和夏季研究。除了教育方面，该项目将加强在研究三角区，包括密歇根大学，NCSU和杜克大学的合作。由于其创新的方法-通过单个分子的可视化来研究材料特性-该项目将对该领域的材料科学和工程产生广泛的影响。

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.