Liu Siqi, Senses Erkan, Jiao Yang, Narayanan Suresh, Akcora Pinar
Department of Chemical Engineering and Materials Science, Stevens Institute of Technology, Hoboken, New Jersey 07030, United States.
Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States.
ACS Macro Lett. 2016 May 17;5(5):569-573. doi: 10.1021/acsmacrolett.6b00089. Epub 2016 Apr 15.
Nanoparticles functionalized with long polymer chains at low graft density are interesting systems to study structure-dynamic relationships in polymer nanocomposites since they are shown to aggregate into strings in both solution and melts and also into spheres and branched aggregates in the presence of free polymer chains. This work investigates structure and entanglement effects in composites of polystyrene-grafted iron oxide nanoparticles by measuring particle relaxations using X-ray photon correlation spectroscopy. Particles within highly ordered strings and aggregated systems experience a dynamically heterogeneous environment displaying hyperdiffusive relaxation commonly observed in jammed soft glassy systems. Furthermore, particle dynamics is diffusive for branched aggregated structures which could be caused by less penetration of long matrix chains into brushes. These results suggest that particle motion is dictated by the strong interactions of chains grafted at low density with the host matrix polymer.
低接枝密度下用长聚合物链功能化的纳米颗粒是研究聚合物纳米复合材料中结构 - 动力学关系的有趣体系，因为它们在溶液和熔体中都会聚集成链，并且在存在游离聚合物链的情况下还会聚集成球体和支化聚集体。这项工作通过使用X射线光子相关光谱测量颗粒弛豫来研究聚苯乙烯接枝氧化铁纳米颗粒复合材料中的结构和缠结效应。高度有序链和聚集体系中的颗粒经历动态非均匀环境，表现出在拥堵软玻璃态体系中常见的超扩散弛豫。此外，对于支化聚集结构，颗粒动力学是扩散性的，这可能是由于长基质链较少渗透到刷中所致。这些结果表明，颗粒运动由低密度接枝的链与主体基质聚合物之间的强相互作用所决定。
