Final Report Summary - TAILOR GRAPHENE (Tailoring Graphene to Withstand Large Deformations)
ERC Advanced Grant TAILOR GRAPHENE is a project that aims to determine the mechanical response of monolayer graphene to extreme axial tensional deformation up to failure and to determine the effect of orthogonal buckling to its overall tensile properties. The achievements of the project are:
- experimental verification of orthogonal buckling with wavelength of 500 nm in suspended graphene flakes (ribbons) at moderate strains;
- experimental verification of formation of wrinkles induced by Poisson’s lateral contraction in supported graphenes (mono- and bi-layers) under uniaxial tensile loading;
- experimental and theoretical verification of axial compression failure of graphene embedded in polymers which occurs at ~0.6% regardless of its size;
- experimental and theoretical verification of axial tensile loading that is free of orthogonal wrinkling/ buckling up to ~1.8% in the case of embedded graphene into polymers; by reducing the width of produced micro-ribbons to less than 4 mm further improvements can be made (over 3%) for the maximum axial strain that the material can withstand without orthogonal wrinkling;
- establishment of protocols for the production of nano and micro-ribbons of variable widths by means of: i) e-beam technology, ii) UV micro lithography/oxygen plasma, and iii) laser cutting;
- development of innovative equipment for the investigation of mechanical behaviour of graphene and of devices that can measure stress at the pico-scale. A picoindenter equipped with Push-to-Pull devices was adjusted under Raman microscope and Raman/Scanning Electron Microscope for simultaneous recording of Raman spectra and sample image during the tensile characterization of suspended graphenes. A micro-tensile tester was adjusted under an Atomic Force Microscope for the investigation of the formation of wrinkle in graphene subjected to uniaxial tensile loading;
- development of a beam-based loading methodology for the equibiaxial strain of graphene;
- the unexpected finding that specific configurations of wrinkling do enhance the load-bearing capacity of few-layer graphene as compared to “flat” specimens;
- development of an analytical methodology to derive strain (and stress) values by monitoring the frequency shifts of graphene phonons with strain and the possibility of establishing stress-strain curves for nanomaterials embedded in polymers both in tension and compression;
- development of generalized mathematical (analytical) models for graphene capable of describing the linear and the (geometrical and material) nonlinear response of graphene for every kind of loading
- development of computational tools (DFT, MD and FEA) for examining the mechanical response of graphene in air and also under the constraints of a surrounding polymer matrix
- development of computation and theoretical/mathematical models to investigate failure mechanisms under strain such as buckling and crumpling. The influence of polymer matrix on the modes of failure of embedded graphene was also examined through MD simulations, revealing a high sensitivity of surface roughness and magnitude of graphene/surface interactions on the onset of buckling;
- development of highly versatile source code to computationally and efficiently manipulate large chiral graphene nanoribbons, that pave the way to in silico experiments that are not present in the state-of-the-art of the field;
Overall, the project has made significant progress in the understanding of the mechanical properties of graphene and the outcomes can be generalised to be used for the study of other 2D materials and ultra-thin membranes.
- experimental verification of orthogonal buckling with wavelength of 500 nm in suspended graphene flakes (ribbons) at moderate strains;
- experimental verification of formation of wrinkles induced by Poisson’s lateral contraction in supported graphenes (mono- and bi-layers) under uniaxial tensile loading;
- experimental and theoretical verification of axial compression failure of graphene embedded in polymers which occurs at ~0.6% regardless of its size;
- experimental and theoretical verification of axial tensile loading that is free of orthogonal wrinkling/ buckling up to ~1.8% in the case of embedded graphene into polymers; by reducing the width of produced micro-ribbons to less than 4 mm further improvements can be made (over 3%) for the maximum axial strain that the material can withstand without orthogonal wrinkling;
- establishment of protocols for the production of nano and micro-ribbons of variable widths by means of: i) e-beam technology, ii) UV micro lithography/oxygen plasma, and iii) laser cutting;
- development of innovative equipment for the investigation of mechanical behaviour of graphene and of devices that can measure stress at the pico-scale. A picoindenter equipped with Push-to-Pull devices was adjusted under Raman microscope and Raman/Scanning Electron Microscope for simultaneous recording of Raman spectra and sample image during the tensile characterization of suspended graphenes. A micro-tensile tester was adjusted under an Atomic Force Microscope for the investigation of the formation of wrinkle in graphene subjected to uniaxial tensile loading;
- development of a beam-based loading methodology for the equibiaxial strain of graphene;
- the unexpected finding that specific configurations of wrinkling do enhance the load-bearing capacity of few-layer graphene as compared to “flat” specimens;
- development of an analytical methodology to derive strain (and stress) values by monitoring the frequency shifts of graphene phonons with strain and the possibility of establishing stress-strain curves for nanomaterials embedded in polymers both in tension and compression;
- development of generalized mathematical (analytical) models for graphene capable of describing the linear and the (geometrical and material) nonlinear response of graphene for every kind of loading
- development of computational tools (DFT, MD and FEA) for examining the mechanical response of graphene in air and also under the constraints of a surrounding polymer matrix
- development of computation and theoretical/mathematical models to investigate failure mechanisms under strain such as buckling and crumpling. The influence of polymer matrix on the modes of failure of embedded graphene was also examined through MD simulations, revealing a high sensitivity of surface roughness and magnitude of graphene/surface interactions on the onset of buckling;
- development of highly versatile source code to computationally and efficiently manipulate large chiral graphene nanoribbons, that pave the way to in silico experiments that are not present in the state-of-the-art of the field;
Overall, the project has made significant progress in the understanding of the mechanical properties of graphene and the outcomes can be generalised to be used for the study of other 2D materials and ultra-thin membranes.