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Study On Characterization And Modification Of Graphene-Based Interfacial Mechanical Behavior

Posted on:2018-01-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:G R WangFull Text:PDF
GTID:1311330518498168Subject:Solid mechanics
Abstract/Summary:PDF Full Text Request
Owing to the unique two-dimensional crystal structure and the atomic scale thickness, graphene exhibits unpresedented physical properties, including striking mechanical performance as well as outstanding electrical, optical and thermal properties, which endow graphene with a bright prospect in fields of functional composite materials, flexible electronics and micro-/nano-eletromechanical systems(MEMS/NEMS). Classic view of conventional composites and devices implies that the macroscopic performance is strongly dependent on the interfacial adhesion quality and the stability. Such an issue could be more significant when the dimensions are downscaled to the nanometer regime, as the weak non-classical forces, such as van der Waals and electrostatic force, tend to be dominant. On the other hand, the atomic level of the thickness and ultra-high specific surface area also create more interface area and induce high sensitivity to the interfacial interactions. Thus, it seems that graphene could provide a fruitful system in which to study novel features of friction and adhesion present only at the nanoscale. In this paper, we have developed a multi-scale experimental platform, combining the macroscopic loading test, microscopic morphology characterization and microscopic strain detection, to investigate interfacial mechanical properties between graphene and different materials. Our results are summarized as following:1. The microstructural behavior of monolayer graphene/PMMA system under axial tension was investigated. The mechanical response of graphene at different strain levels was recorded by Raman spectroscopy. The elastic stress transfer and shear sliding were analyzed by the nonlinear shear-lag model, where the key mechanical parameters such as interface shear strength and interface stiffness could be obtained. The interfacial stability under multiple cyclic loading conditions was further discussed, and the evolution of the surface morphology characterized by atomic force microscopy (AFM)assisted the interpretation of the microscopic mechanism. Furthermore, chemical strategy was employed to modify the bonding type between graphene and matrix and tune the interfacial mechanical properties, to eventually achieve the interfacial optimal design for high-performance composite.2. The interfacial mechanical behavior of PMMA / graphene / PMMA "sandwich"system during biaxial compression was studied at microscale. The mechanical response of graphene at different strains was detected by Raman spectroscopy, and the microstructural evolution featuring three stages was identified. In the elastic stage, the microscopic strain in graphene was recorded at a given load to deduce the apparent compressive modulus. In the Euler buckling stage, the influence of the size and the layer numbers on the critical buckling strain was analyzed and the interfacial stability under multiple cyclic loadings was revealed. When the interfacial debonding occurred,Raman spectroscopy was used to characterize the failure mode. The theoretical model was established to describe the micro-mechanical behavior and to extract the mechanical parameters such as critical debonding strain.3. The interfacial mechanical properties of monolayer graphene between silicon substrate were studied via the combination of bubbling test, probe technique and Raman spectroscopy, where the out-of-plane displacement was characterized by AFM and Raman spectroscopy was utilized to monitor the controllable growth of shear zone on the silicon substrate. On the basis of Hencky solution, the boundary condition was corrected considering the shear deformation outside the hole to enable the deduction of the interfacial shear stress between graphene and the silicon substrate. Pressure was further increased to reach the interfacial delamination state, where the interface adhesion energy could be obtained combined with the ideal gas equation and energy analysis. The effects of interfacial shear sliding and the boundary condition were considered to elucidate the delamination behavior and the final bubble morphology.4. The interlayer coupling between graphene layers were measured and chemically tailored. Based on the bubbling test, bilayer graphene could be controllably loaded and the propagation of the interlayer shear zone was monitored by Raman spectroscopy.Combined with the modified Hencky model, the accurate measurement of the interlayer shear stress of bilayer graphene was achieved. This is the first measurement of the interlayer shear stress for the thinnest structures possible. Boron doping was performed to tune the interlayer coupling, as identified by Raman shear mode together with the linear chain model with regard to the interlayer shear constant. Nanoindentation test was adopted to explore the effect of interlayer coupling on the overall mechanical behavior bilayer graphene.
Keywords/Search Tags:graphene, interfacial mechanical property, microscopic deformation, experimental measurement and characterization, interfacial design
PDF Full Text Request
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