Macromolecular Science and Engineering and ‡Department of Material Science and Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
ACS Nano. 2014 Jan 28;8(1):607-13. doi: 10.1021/nn405233a. Epub 2014 Jan 2.
Diverse processes that include energy conversion, wettability, lubrication, adhesion, and surface-directed phase separation in mixtures fundamentally depend on the structure and dynamics of materials' surfaces and interfaces. We report an unusual phenomenon wherein the surface viscosity of polymer nanocomposites of polystyrene (PS), polyvinyl methyl ether (PVME), and PS-coated gold nanoparticles (PS/PVME/PS-Au) is over an order of magnitude smaller than that of the neat miscible PS/PVME blend. Our X-ray photon correlation spectroscopy studies of the surface dynamics also reveal that the polymer chains manifest dynamics associated with two separate average compositional environments: a PVME-rich region, significantly in excess of its bulk concentration, and a separate PS-rich environment, where the dynamics are approximately 2 orders of magnitude slower. The unusually rapid surface dynamics in the PS/PVME/PS-Au nanocomposite are due largely to the excess PVME chains and the polymer/brush-coated nanoparticle interactions at the free surface.
多种过程，包括能量转换、润湿性、润滑、粘附和混合物中的表面定向相分离，从根本上取决于材料表面和界面的结构和动力学。我们报告了一种不寻常的现象，即在聚苯乙烯（PS）、聚甲基乙烯基醚（PVME）和 PS 包覆的金纳米粒子（PS/PVME/PS-Au）的聚合物纳米复合材料的表面粘度比同类可混溶的 PS/PVME 混合物高一个数量级以上。我们对表面动力学的 X 射线光子相关光谱研究还表明，聚合物链表现出与两种不同平均组成环境相关的动力学：一个 PVME 丰富的区域，明显超过其体相浓度，和一个单独的 PS 丰富的环境，其中动力学大约慢 2 个数量级。PS/PVME/PS-Au 纳米复合材料中异常快速的表面动力学主要归因于过量的 PVME 链和聚合物/刷涂纳米粒子在自由表面的相互作用。
