Multi-Scale in situ Mechanical Characterization of Low-Dimensional Carbon Nanomaterials and Their Hierarchical Structures

低維碳納米材料及其多級結構的多尺度原位力學研究

Student thesis: Doctoral Thesis

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Award date4 Sep 2019

Abstract

Due to the intriguing characteristics and outstanding physical and chemical properties, low-dimensional carbon nanomaterials, such as carbon nanotube, single, few-layer and multi-layer graphene and other carbon nanomaterials related hierarchical structures hold great promise for a variety of mechanical, electrical, electrochemical, thermal, optical and many other functional applications. Graphene and single-walled carbon nanotube (SWCNT) have been theoretically predicted to be with high tensile strength and Young’s modulus. But the experimental study of their mechanical properties is still very lacking due to the challenge of the manipulating of nanomaterials and the mechanical testing techniques. Their applications like wearable flexible electronics often involve mechanical loadings and deformations, which requires a comprehensive and in-depth understanding of their mechanical behavior and structural reliability. Also, preliminary studies suggested that the outstanding mechanical properties of some carbon nanomaterials could lead to unusual physical properties and unprecedented functions (the so-called “strain engineering” applications). So the systematic mechanics’ study of carbon nanomaterials (including the elastic properties and the fracture mechanism) are essential for technological perspectives in their reliable and high- performance device applications.

Here, the mechanical behaviors of and the low-dimensional carbon nanomaterials building blocks and their hierarchical structures (including graphene/graphene oxide, carbon nanotube, and graphene hybrid films) were comprehensively investigated based on our developed multi-scale in situ quantitative micro-/nanomechanical characterization techniques. Chemical vapor deposition synthesized monolayer graphene was demonstrated with good resilience and with high tensile strength through uniform and controllable strain applied using our tensile platform. Molecular dynamics (MD) simulations results confirmed the fracture at the clamping ends which was in accordance with the experimental results. In situ tensile testing on multilayer graphene nanosheets showed a decreasing trend of the tensile strength as the thickness (or layers) increases. High-resolution TEM analysis showed obvious delamination between the atomic layers. Additionally, the graphene oxide nanosheets assemblies with different thickness were also investigated with our in situ tensile testing platform. The horizontal folds would be tensioned unfolded and flattened during the tensile testing process.

Besides, the Ag nanowires were also incorporated with graphene to form a hybrid film through a spin coating method. The hybrid films showed better electro-mechanical responses compared with pure Ag nanowires films and pure graphene films during macroscale bending tests. in situ transmission electron microscope tensile testing results of the hybrid films at microscale showed a good interface connection between the graphene and the Ag nanowires. In addition, the Ag nanowires underwent large plastic deformations during the testing process.