Quantification of stress transfer in a model cellulose nanocrystal/graphene bilayer using Raman spectroscopy

Graphene and cellulose possess a multitude of unique and useful properties for applications in electronics, sensors and composites which has led to significant scientific interest over the past 5–10 years. Despite this interest, there has been no experimental work investigating the interface or stress transfer efficiency between these materials, which limits future developments in this field. With the aim of investigating this interface, we have created a model bilayer composite, consisting of a tunicate derived cellulose nanocrystal (T-CNC) film and a monolayer of graphene produced by chemical vapour deposition. Raman spectroscopy has been used to monitor the four-point bending of this model bilayer composite. Shifts in the position of Raman bands, unique for both the cellulose and graphene components of this model composite, are recorded. Using a novel analysis of these Raman band shifts, we have formed an expression which deconvolutes the total stress transfer efficiency of the model system. Using this deconvolution, a stress transfer efficiency of 66% has been derived at the cellulose/graphene interface. In addition, splitting of the graphene Raman G band has allowed calculation of the shear strain in the graphene, which is assumed to be equal to that at the cellulose-graphene interface. The individual T-CNCs in the reference samples showed location dependent preferential orientations. The film was found to be stiffer when the T-CNCs were oriented parallel to the loading axis. It was intended that the varying stiffness of the cellulose film could be used to analyse the effects of underlying film stiffness on stress transfer efficiency, but conclusions from this test were limited. The detailed interface analysis presented here will help to inform design in future cellulose/graphene devices.