Moll Joseph, Kumar Sanat K, Snijkers Frank, Vlassopoulos Dimitris, Rungta Atri, Benicewicz Brian C, Gomez Enrique, Ilavsky Jan, Colby Ralph H
Department of Chemistry, Columbia University, 5000 Broadway, New York, New York 10027, United States.
Department of Chemical Engineering, Columbia University, 500 West 120th Street, New York, New York 10027, United States.
ACS Macro Lett. 2013 Dec 17;2(12):1051-1055. doi: 10.1021/mz400447k. Epub 2013 Nov 14.
Flow-fields are typically used to intimately mix large μm-sized particles with polymer melts. Here we show, using rheology, X-ray scattering, and electron microscopy, that shear flows do not improve the spatial dispersion or ordering of spherical nanoparticles (NP) grafted with polymer chains over the ranges of flow fields realizable in our experiments in the melt state. In the absence of flow, grafted NPs robustly self-assemble into a variety of superstructures when they are added to a homopolymer matrix with the same chemistry as the NP grafts. We find that isolated particles and spherical NP clusters remain dispersed but do not flow align. On the other hand, anisotropic NP assemblies initially break and their constituent building blocks (strings or sheets) flow-align locally. At very large strains, they coarsen into large aggregates, reflecting the dominance of interparticle attractions over flow fields and thermal energy.
流场通常用于使大尺寸微米级颗粒与聚合物熔体充分混合。在此我们利用流变学、X射线散射和电子显微镜表明，在我们实验可实现的熔体状态流场范围内，剪切流不会改善接枝有聚合物链的球形纳米颗粒（NP）的空间分散或排列。在无流动的情况下，当将接枝的NP添加到与NP接枝具有相同化学组成的均聚物基体中时，它们能稳健地自组装成各种超结构。我们发现孤立的颗粒和球形NP簇保持分散但不发生流动取向。另一方面，各向异性的NP聚集体最初会破裂，其组成结构单元（线或片）会局部流动取向。在非常大的应变下，它们会粗化为大的聚集体，这反映了颗粒间吸引力对流场和热能的主导作用。
