Carbon nanomaterials, such as graphene and graphene oxide, have outstanding mechanical strength, stiffness, and toughness that surpass those of materials currently used to build structures. However, these properties are limited to the nanoscale and have not yet been attained in macroscopic composites containing carbon nanomaterials. To integrate the mechanical properties of nanocarbons into their macroscopic composites, it is important to understand how the mechanical properties of the composite at each length scale are influenced by the structure and surface chemistry of the nanocarbon filler and its interfacial interactions with the constituents. Using graphene oxide (GO) as a model carbon nanomaterial, this thesis investigates how the nanoscale mechanical properties of GO-based nanocomposites can be modulated through its structure and interfacial interactions within the composite.The effect of chemical structure on the stiffness and plasticity of single-layer GO was investigated through nanomechanical experiments. While stiffness decreases as the functionalization level of GO increases, this can be mitigated by tailoring the functional group distribution of GO to increase its plasticity. Under nanomechanical load, epoxide groups can transform into ether groups, providing an intrinsic toughening mechanism that imparts local ductility and damage-tolerance to single-layer GO at the atomic level. An extrinsic toughening mechanism was introduced by modifying single-layer GO with an ultrathin layer of polyvinyl alcohol, which can enable microscale crack bridging. Due to extensive hydrogen-bonding interfacial interactions between the oxidized domains of GO and the polymer, a toughness comparable to single-layer graphene was achieved, and a three-fold increase in the load-bearing ability of GO was observed. These nanoscale studies prompted the exploration of how GO structure at the single-layer level affects the mechanical properties of its bulk structures. While porosity, an inherent structural aspect of GO, dramatically lowers stiffness and strength at the single-layer level, these mechanical properties are much less sensitive in multilayer films assembled from porous GO sheets. The co-assembly of porous and pristine GO sheets surprisingly enhances the stiffness of multilayer GO films, as porous sheets can achieve more compliant packing within the film and effectively serve as a binder to strengthen interlayer interactions.

Creator

• Mao, Lily

DOI

• https://doi.org/10.21985/n2-8fkq-ba67

Subject

• Chemistry

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16272
• etdadmin_upload_929408

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright