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dc.contributor.authorCastilho, Cintia J.en_US
dc.contributor.authorLi, Dongen_US
dc.contributor.authorXie, Yihengen_US
dc.contributor.authorGao, Huajianen_US
dc.contributor.authorHurt, Robert H.en_US
dc.identifier.citationCastilho, C. J., Li, D., Xie, Y., Gao, H. & Hurt, R. H. (2021). Shear failure in supported two-dimensional nanosheet van der Waals thin films. Carbon, 173, 410-418.
dc.description.abstractLiquid-phase deposition of exfoliated 2D nanosheets is the basis for emerging technologies that include writable electronic inks, molecular barriers, selective membranes, and protective coatings against fouling or corrosion. These nanosheet thin films have complex internal structures that are discontinuous assemblies of irregularly tiled micron-scale sheets held together by van der Waals (vdW) forces. On stiff substrates, nanosheet vdW films are stable to many common stresses, but can fail by internal delamination under shear stress associated with handling or abrasion. This "re-exfoliation" pathway is an intrinsic feature of stacked vdW films and can limit nanosheet-based technologies. Here we investigate the shear stability of graphene oxide and MoSe₂ nanosheet vdW films through lap shear experiments on polymer-nanosheet-polymer laminates. These sandwich laminate structures fail in mixed cohesive and interfacial mode with critical shear forces from 40 - 140 kPa and fracture energies ranging from 0.2 - 6 J/m². Surprisingly these energies are higher than delamination energies reported for smooth peeling of ordered stacks of continuous 2D sheets, which we propose is due to energy dissipation and chaotic crack motion during nanosheet film disassembly at the crack tip. Experiment results also show that film thickness plays a key role in determining critical shear force (maximum load before failure) and dissipated energy for different nanosheet vdW films. Using a mechanical model with an edge crack in the thin nanosheet film, we propose a shear-to-tensile failure mode transition to explain a maximum in critical shear force for graphene oxide films but not MoSe₂ films. This transition reflects a weakening of the substrate confinement effect and increasing rotational deformation near the film edge as the film thickness increases. For graphene oxide, the critical shear force can be increased by electrostatic cross-linking achieved through interlayer incorporation of metal cations. These results have important implications for the stability of functional devices that employ 2D nanosheet coatings.en_US
dc.rights© 2020 Elsevier Ltd. All rights reserved.en_US
dc.subjectEngineering::Mechanical engineeringen_US
dc.titleShear failure in supported two-dimensional nanosheet van der Waals thin filmsen_US
dc.typeJournal Articleen
dc.contributor.schoolSchool of Mechanical and Aerospace Engineeringen_US
dc.subject.keywordsTwo-dimensional Materialsen_US
dc.description.acknowledgementWe acknowledge financial support from National Institute of Environmental Health Sciences Superfund Research Program P42 ES013660 through a project on barrier films for personal protective equipment, and a seed grant from the Institute at Brown for Environment and Society (IBES) on protective barrier technologies. The modeling part of the work was also supported by a graduate fellowship to D.L. from the China Scholarship Council (CSC).en_US
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