Stress-transfer from polymer substrates to monolayer and few-layer graphenes
In the present study the stress transfer mechanism in graphene-polymer systems under tension is examined experimentally using the technique of laser Raman microscopy. We discuss in detail the effect of graphene edge geometry, lateral size and thickness which need to be taken under consideration when using graphene as a protective layer or filler. The systems examined comprised of graphene flakes with large length (over ~50 microns) and thickness of one to three layers simply-deposited onto PMMA substrates which were then loaded to tension up to ~1.60% strain. The stress transfer profiles were found to be linear while the results show that large lateral sizes of over twenty microns are needed in order to provide effective reinforcement at levels of strain higher than 1%. Moreover, the stress-built up has been found to be quite sensitive to both edge shape and geometry of the loaded flake. Finally, the obtained values of interfacial shear stress (ISS) as well as the transfer lengths, were found to increase linearly with the increase of graphene layers as predicted by a simple balance-of-forces analysis. The outcomes of the present study provide crucial insight on the issue of stress transfer from polymer to nano-inclusions as a function of edge geometry, lateral size and thickness in a number of applications.