Aoyama Shigeru, Park Yong Tae, Macosko Christopher W, Ougizawa Toshiaki, Haugstad Greg
Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue S.E., Minneapolis, Minnesota 55455, United States.
Langmuir. 2014 Nov 4;30(43):12950-9. doi: 10.1021/la502553q. Epub 2014 Oct 21.
The interfacial adhesion between polymer and nanofiller plays an important role in affecting the properties of nanocomposites. The detailed relationship between interfacial adhesion and bulk properties, however, is unclear. In this work, we developed an atomic force microscopy (AFM)-based abrasive scanning methodology, as applied to model laminate systems, to probe the strength of interfacial adhesion relevant to poly(ethylene terephthalate) (PET)/graphene or clay nanocomposites. Graphite and mica substrates covered with ∼2 nm thick PET films were abrasively sheared by an AFM tip as a model measurement of interfacial strength between matrix PET and dispersed graphene and clay, respectively. During several abrasive raster-scan cycles, PET was shear-displaced from the scanned region. At temperatures below the PET glass transition, PET on graphite exhibited abrupt delamination (i.e., full adhesive failure), whereas PET on mica did not; rather, it exhibited a degree of cohesive failure within the shear-displaced layer. Moreover, 100-fold higher force scanning procedures were required to abrade through an ultimate "precursor" layer of PET only ∼0.2-0.5 nm thick, which must be largely disentangled from the matrix polymer. Thus, the adhesive interface of relevance to the strength of clay-filler nanocomposites is between matrix polymer and strongly bound polymer. At 90 °C, above the bulk PET glass transition temperature, the PET film exhibited cohesive failure on both graphite and mica. Our results suggest that there is little difference in the strength of the relevant interfacial adhesion in the two nanocomposites within the rubbery dynamic regime. Further, the bulk mechanical properties of melt mixed PET/graphene and PET/clay nanocomposites were evaluated by dynamic mechanical analysis. The glassy dynamic storage modulus of the PET/clay nanocomposite was higher than that of PET/graphene, correlating with the differences in interfacial adhesion probed by AFM.
聚合物与纳米填料之间的界面粘附在影响纳米复合材料性能方面起着重要作用。然而，界面粘附与整体性能之间的详细关系尚不清楚。在这项工作中，我们开发了一种基于原子力显微镜（AFM）的研磨扫描方法，应用于模拟层压系统，以探测与聚对苯二甲酸乙二酯（PET）/石墨烯或粘土纳米复合材料相关的界面粘附强度。覆盖有2 nm厚PET薄膜的石墨和云母基底分别被AFM针尖进行研磨剪切，作为基质PET与分散的石墨烯和粘土之间界面强度的模型测量。在几个研磨光栅扫描循环中，PET从扫描区域发生剪切位移。在低于PET玻璃化转变温度时，石墨上的PET表现出突然分层（即完全粘附失效），而云母上的PET则没有；相反，它在剪切位移层内表现出一定程度的内聚破坏。此外，需要100倍更高的力扫描程序才能磨穿仅0.2 - 0.5 nm厚的PET最终“前体”层，该层必须与基质聚合物大量解缠结。因此，与粘土 - 填料纳米复合材料强度相关的粘附界面位于基质聚合物与强结合聚合物之间。在90°C，高于PET本体玻璃化转变温度时，PET薄膜在石墨和云母上均表现出内聚破坏。我们的结果表明，在橡胶态动态范围内，两种纳米复合材料中相关界面粘附强度几乎没有差异。此外，通过动态力学分析评估了熔融共混的PET/石墨烯和PET/粘土纳米复合材料的整体力学性能。PET/粘土纳米复合材料的玻璃态动态储能模量高于PET/石墨烯，这与AFM探测的界面粘附差异相关。
