Molecular Visualization: Spreading Kinematics and Dynamics

在固体表面铺展聚合物薄膜是一项基础研究和技术研究。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传播的方式。这些导致了对润湿的宏观理解；然而，分子机制在很大程度上仍然未知。因此，显然需要开发能够在扩散过程中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与荧光显微镜相结合的分子扩散监测系统。还建议使用支化聚合物分子作为模型系统，可以通过选择的技术可视化。该项目将解决四个基本问题。(i)局限于表面的聚合物链的构象和排列是什么？（ii）聚合物分子在二维空间的扩散运动学及其与前驱体膜前缘运动的关系是什么？（iii）润湿动力学的驱动力和耗散通道及其相对贡献是什么？（iv）表面流动的分子模式是什么及其与底物表面结构的关系？这项工作将促进对润湿分子机制的基本理解，也将为操纵分子结构来控制润湿动力学提供实用的指导。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。北卡罗来纳大学教堂山分校以定期科学研讨会和夏季研究的形式与当地高中建立了互动，这是一个具有更广泛影响的特殊领域。除了教育方面，该项目还将加强包括北卡罗来纳大学、北卡州立大学和杜克大学在内的三角研究地区的合作。由于其创新的方法-通过单个分子的可视化研究材料特性-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.