Stress-transfer from polymer substrates to monolayer and few-layer graphenes

Abstract

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. The systems examined comprised of graphene flakes with large length (over ~50 microns) and thickness of one to three layers simplydeposited 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 transfer lengths were found to increase with the increase of graphene layers. 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.

Tunable macroscale structural superlubricity in two-layer graphene via strain engineering

“…The shape of the stress-transfer curve from the polymer to the inclusion for the bottom layer (figure 3a) is, as expected, governed by polymer-graphene shearing, that leads to stress buildup from the flake edges and the attainment of a plateau at the middle of the flake 25 . This mechanism is a result of the strain transfer with friction, which leads to linear strain profiles at the edges with constant interlayer frictional stress and the length required for strain transfer increases with the increase in the applied load 31 . As it is discussed below this is a crucial point that has not received attention and holds for the case of a graphene-graphene interface.…”

Efficient Mechanical Stress Transfer in Multilayer Graphene with a Ladder-like Architecture

“…It is worth mentioning here that in the past we have observed a dramatic improvement in the stress transfer for bulk graphite embedded into a thin layer of polymer (Table ) under tensile strain using the 2D band as a strain gauge. Also, it has been recently reported by Androulidakis et al that normal stress could be transmitted directly to the embedded graphene depending on specimen fabrication and handling. To assess the contribution of axial stress generated by shear loading vis-à-vis those transmitted directly to the embedded graphene through adhesion at the ends in our ladder-like architecture, we have analyzed the problem at two different length scales and approaches.…”

“…It has been proved , that the axial stress is transferred to an embedded single graphene flake through shear at the graphene–polymer interface. Similar to fibrous composites, to efficiently transfer the applied strain at the composite in graphene, a critical length of reinforcement ( L c )defined as twice the distance from the graphene edge toward the inner part of the flake until the strain reaches its maximum valueof at least 10 μm is usually needed . As a consequence, if the available length of a graphene flake for stress transfer in the axial direction is less than L c /2 for an applied stress/strain at the composite, then only a fraction of the applied stress/strain is transmitted to the flake, decreasing the measured Raman mode strain sensitivities accordingly.…”

Comprehensive Enhancement in Thermomechanical Performance of Melt-Extruded PEEK Filaments by Graphene Incorporation

“…This is due to the improved dispersion of the GnP fillers inside the PEEK matrix and the formation of a strong interface between fillers and matrix through hydrogen bonding and π-π* interactions. These factors contribute to optimizing the stress transfer from the PEEK matrix to the graphene fillers, inducing a strong reinforcing action of the GnP fillers [55][56][57]. The improvement in elongation at break (31%) and tensile strength (34%) at 1 wt.% of GnP loading demonstrated significantly better results than the previous reports [6,58,59].…”

“…This can be associated with the enhanced aggregates of the GnP fillers that might have acted as stress concentration sites (see Supplementary Figure S2d), resulting in a decline in the mechanical performance. Now it is well established in the literature that at filler concentration > 1 wt.%, graphene agglomeration is unavoidable [57,60]. Summarizing, the extruded filaments of PEEK with 1.0 wt.% of GnPs concentration (PEEK-GnP1.0) presented the best mechanical performance compared to the other two nanocomposite samples that are PEEK-GnP0.5 and PEEK-GnP3.0.…”