A study of graphene and MXene and their composites: fabrication, mechanical properties, strain sensing, and electromagnetic interference shielding application

Student thesis: Doctoral Thesis

Abstract

In this thesis, two kinds of representative two-dimensional (2D) materials, graphene and MXene in the form of 2D assembly and 3D assembly are studied, with emphasis on their mechanical properties, strain sensing, and electromagnetic interference (EMI) shielding performances. The research goals in this thesis include the following aspects: (1) developing flexible and lightweight 2D & 3D composite materials (i.e., films or foams) based on two kinds of representative nanomaterials (graphene and MXene) via efficient, facile, and scalable synthetic routes (i.e., vacuum filtration, pyrolysis, and dip-casting); (2) advancing the understanding of structure-property-function correlation of the above 2D & 3D composite materials in the applications of EMI shielding and strain sensing. The major achievement in this thesis can be highlighted by the following aspects: (1). The in-depth study of the mechanical properties of 3D graphene foam prepared by dip-coating and pyrolysis method; (2) developing lightweight and flexible 3D carbon nanotubes/graphene composite foam with tunable mechanical properties and EMI shielding performance; (3) developing flexible and lightweight 3D graphene composite foam with tunable 3D hierarchical cellular structure and EMI shielding performance by introducing multifunctional species into carbon foam framework; (4) developing 2D MXene film with laminar structure via vacuum filtration method, and elaborate the role of laminar structure in the tensile properties of MXene films; (5) developing MXene-tissue composite paper with 3D porous structure, and elaborate the influence of such porous structure in the application when the MXene-tissue composite paper is applied in the strain sensing and EMI shielding. The thesis starts with a critical review on 2D nanomaterials-based cellular materials (2DCMs) from fabrication, characterization of mechanical properties, and the engineering approaches to improving the flexibility (Chapter 1). Advancing the understanding of mechanical properties of 2D-CMs provides us a guideline for the design and fabrication 2DCMs based devices for industrial applications such as strain sensing, electromagnetic interference shielding. Here we use the most representative 2D material, graphene, as an example to explain the structure-property-function correlations of cellular graphene (CG). Several state-of-the-art approaches for fabricating CG with emphasis on the engineering of tailored mechanical properties are systematically and critically analyzed. The structure-property-function correlations of 2D-CMs are largely determined by the synthetic routes. In particular, we discuss the mechanical behaviors of graphene foams prepared by sacrificial template directed method (Chapter 2). The mechanical properties of as-produced graphene foam were studied by uniaxial tension, compression and three-point bending methods. The experimental results show these graphene foams fail in the brittle manner under tension, compression and bending. The lack of flexibility of graphene foams is attributed to the weak interactions between graphene sheets. To improve the flexibility of graphene foam, carbon nanotubes are introduced as binding agent to strengthen the interactions between graphene sheets. The mechanical durability to cyclic compression is enhanced significantly when the mass ratio of CNT-GO reaches more than 5:1. As an extreme case, pure CNT foam has the best mechanical durability with an ultra-low density of 0.7 mg/cm3, and exhibits an excellent EMI shielding effectiveness of 44 dB and a very high value of normalized EMI shielding effectiveness of 32,832 dB cm2 g-1, making it to be a promising candidate of lightweight and flexible EMI shielding materials. Although CNT-graphene foam has demonstrated improved flexibility than pure graphene foam, its cellular structures is easy to be destroyed under multi-deformations or large external force; as a result, the EMI shielding performance might be compromised. To improve the mechanical strength and durability without scarifying EMI shielding performance, we develop a specifically engineered variant of carbonized melamine foam (cMF) by systematic structural modifications with Au nanoparticles, graphene (G), Fe3O4 (IO) and poly(dimethyl siloxane) (PDMS) (Chapter 3). The as-prepared lightweight and flexible 3D graphene-involved composite has tunable 3D hierarchical architecture for highefficiency electromagnetic interference (EMI) shielding. The collective EMI shielding effectiveness (SE) of cMF-Au-G-IO/PDMS film with a thickness of 2 mm is determined as 30.5 dB in X band (8.2-12.4 GHz). SE is further raised up to 52.5 dB when the film thickness is increased to 10 mm. Besides graphene, a recent emerging family of 2D materials known as transition metal carbides or nitrides (MXenes), has attracted extensive research interest because these materials display excellent mechanical, electronic, thermoelectric, and optical properties. As the most representative member in MXene family, Ti3C2Tx, and the mechanical properties of its 2D assembly, Ti3C2Tx films are investigated (Chapter 4). The tensile behavior of Ti3C2Tx (MXene) films was for first time studied in detail. Ti3C2Tx films with various thicknesses (2-17 ┬Ám) were prepared by vacuum filtration method. Quasi-static tension and cyclic tension tests were performed to investigate deformation and fracture mechanism of Ti3C2Tx films. Followed by the study of mechanical behaviors of Ti3C2Tx films, the applications of Ti3C2Tx in EMI shielding and pressure sensing are explored by preparation of a Ti3C2Tx-tissue composite paper via a facile and economic dip-coating method (Chapter 5). The as-prepared composite paper possesses a 3D interconnected porous structure made of mcirofibers of cellulose tissue paper. The EMI shielding effectiveness and pressure sensitivity are adjustable by stacking various layers of Ti3C2Tx-tissue papers. The fabricated Ti3C2Tx-tissue composite paper not only shows a high EMI shielding performance of 45 dB, far exceeding the requirement for commercial use (20 dB), but also has an excellent pressure sensitivity of 39.8 kPa-1, allowing it to detect human's subtle physiological signals such as wrist pulse and breath.
Date of AwardDec 2019
Original languageAmerican English

Keywords

  • 2D materials
  • graphene
  • MXene
  • mechanical properties
  • pressure sensing
  • EMI shielding.

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