Materials Science Centre, School of Materials, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
ACS Nano. 2011 Apr 26;5(4):3079-84. doi: 10.1021/nn2002079. Epub 2011 Mar 17.
Model composite specimens have been prepared consisting of a graphene monolayer sandwiched between two thin layers of polymer on the surface of a poly(methyl methacrylate) beam. It has been found that well-defined Raman spectra can be obtained from the single graphene atomic layer and that stress-induced Raman band shifts enable the strain distribution in the monolayer to be mapped with a high degree of precision. It has been demonstrated that the distribution of strain across the graphene monolayer is relatively uniform at levels of applied strain up to 0.6% but that it becomes highly nonuniform above this strain. The change in the strain distributions has been shown to be due to a fragmentation process due to the development of cracks, most likely in the polymer coating layers, with the graphene remaining intact. The strain distributions in the graphene between the cracks are approximately triangular in shape, and the interfacial shear stress in the fragments is only about 0.25 MPa, which is an order of magnitude lower than the interfacial shear stress before fragmentation. This relatively poor level of adhesion between the graphene and polymer layers has important implications for the use of graphene in nanocomposites, and methods of strengthening the graphene-polymer interface are discussed.
已经制备了由夹在聚合物薄层之间的单层石墨烯组成的模型复合材料样品，该聚合物薄层位于聚甲基丙烯酸甲酯梁的表面。研究发现，从单层石墨烯中可以获得定义明确的拉曼光谱，并且应力诱导的拉曼带位移使得可以高精度地映射单层中的应变分布。已经证明，在施加应变高达 0.6%的水平下，横跨石墨烯单层的应变分布相对均匀，但是在高于该应变的水平下，应变分布变得非常不均匀。应变分布的变化归因于由于裂纹的发展而导致的断裂过程，最有可能在聚合物涂层层中，而石墨烯保持完整。裂纹之间的石墨烯中的应变分布大致呈三角形，并且在碎片中的界面剪切应力仅约为 0.25 MPa，这比断裂前的界面剪切应力低一个数量级。石墨烯和聚合物层之间的这种相对较差的粘附水平对在纳米复合材料中使用石墨烯具有重要意义，并且讨论了增强石墨烯-聚合物界面的方法。
