Abstract
Industrially scalable methods for the production of graphene and other nanographites are needed to achieve cost-efficient commercial products. At present, there are several available routes for the production of these materials but few allow large-scale manufacturing and environmentally friendly low-cost solvents are rarely used. We have previously demonstrated a scalable and low-cost industrial route to produce nanographites by tube-shearing in water suspensions. However, for a deeper understanding of the exfoliation mechanism, how and where the actual exfoliation occurs must be known. This study investigates the effect of shear zone geometry, straight and helical coil tubes, on this system based on both numerical simulation and experimental data. The results show that the helical coil tube achieves a more efficient exfoliation with smaller and thinner flakes than the straight version. Furthermore, only the local wall shear stress in the turbulent flow is sufficient for exfoliation since the laminar flow contribution is well below the needed range, indicating that exfoliation occurs at the tube walls. This explains the exfoliation mechanism of water-based tube-shear exfoliation, which is needed to achieve scaling to industrial levels of few-layer graphene with known and consequent quality.
Highlights
To achieve cost-efficient commercial products utilizing the excellent properties of carbon nanomaterials, it is necessary to develop industrially scalable methods for the production of nanographites; such as graphene, few-layer graphene and graphite nanoplatelets[1,2,3]
In previous work[3] we have demonstrated a scalable and low-cost industrial route to produce nanographites based on hydrodynamic tube-shearing in water suspension
The current report is a study of the effect on shear zone geometry in hydrodynamic tube-shear exfoliation to obtain a deeper understanding of the exfoliation mechanism and the requirements needed to achieve efficient large-scale mechanical exfoliation to nanographites in water suspensions
Summary
To achieve cost-efficient commercial products utilizing the excellent properties of carbon nanomaterials, it is necessary to develop industrially scalable methods for the production of nanographites; such as graphene, few-layer graphene and graphite nanoplatelets[1,2,3]. Xiao-Li Li et al.[23] demonstrated a method to identify the layer number of graphene flakes on Silicon/Silicon dioxide substrates in Raman by comparing the intensity ratio of the Si peak of the Si/SiO2 substrate underneath the graphene flakes, and the Si peak from the bare Si/SiO2 substrate. The shear zone, a straight tube, resulted in a wide flake-size distribution of wrinkled or partly wrinkled nanometer-thick flakes These properties have been shown to have great potential in energy storage applications where high electrical conductivity is needed together with high surface area[25,26,27]. The current report is a study of the effect on shear zone geometry in hydrodynamic tube-shear exfoliation to obtain a deeper understanding of the exfoliation mechanism and the requirements needed to achieve efficient large-scale mechanical exfoliation to nanographites in water suspensions
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