Date of Graduation
12-2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Engineering (PhD)
Degree Level
Graduate
Department
Mechanical Engineering
Advisor/Mentor
Nair, Arun K.
Committee Member
Chen, Jingyi
Second Committee Member
Millett, Paul C.
Third Committee Member
Wejinya, Uche C.
Keywords
Carbon; Carbyne; Nanomaterials
Abstract
There is a broad range of carbon-based nanomaterials with different dimensions and mechanical properties. Among these are 3D carbon nanotubes (CNTs), 2D cyclo[18]carbon (C18) rings, and 1D carbyne chains. Carbyne has the highest stiffness, but it is highly reactive when not encapsulated. This dissertation uses molecular dynamics (MD) and density functional theory (DFT) to investigate the interface, thermal, and mechanical properties of these low dimensional carbon materials.
In this dissertation, MD is used to predict the mechanical and thermal properties of carbon-based materials including carbyne, CNTs, C18 rings, and hybrid C18-carbyne structures. DFT is utilized to investigate interface properties of carbyne on Ni and Cu(111) surfaces and validate properties of the carbyne on these surfaces predicted by MD. Based on the predicted interface, thermal, and mechanical properties of the materials, this dissertation also focuses on the low dimensional materials’ possible use as components of nanocomposites and their high temperature mechanical properties. Cu matrix nanocomposites with the 1D carbyne and 1D-2D C18-carbyne are developed and the mechanical properties of the nanocomposite under tensile loading are predicted. Then, cumulenic and polyynic carbyne are pyrolyzed to determine how heating the chains affects their mechanical properties.
During investigation of the carbyne’s interface properties, it is observed that carbyne does not maintain cumulenic or polyynic bonding on Ni(111) without dielectric screening via graphene or CNTs, while the chain maintains cumulenic bonding on the Cu(111) surface. When compared to the other low dimensional materials, carbyne requires the largest force to fracture during tensile testing and has the highest thermal conductivity. The thermal conductivity of these low dimensional materials on a Cu surface is also studied, and carbyne again has the highest thermal conductivity. Metallic interface effects on the low dimensional materials’ mechanical properties are also investigated. During comparison of the mechanical properties of the low dimensional materials on Ni and Cu(111) surfaces during three-point bending, carbyne encapsulated in a CNT is the stiffest structure on both metals and shields the carbyne from the Ni surface.
We then predict the mechanical properties when the low dimensional materials are embedded in a Cu matrix. Cu matrix nanocomposites with carbyne and C18-carbyne are generated and studied at room and elevated temperatures. The Cu-C18-carbyne nanocomposite has the highest elastic modulus at 300K due to its 2D ring interface with the Cu and thus high adsorption energy. However, at 600K and 900K, the 1D carbyne placed in a line defect of the Cu has the highest elastic modulus due to its smaller displacement of Cu atoms in the matrix. It is also determined that pyrolysis can increase carbyne’s resistance to compression due to the formation of graphitic nanostructures at high temperatures.
The thermal and mechanical properties of carbon-based materials are highly dependent on their dimensions, interfaces, and bonding. This study demonstrates that carbyne and its hybrid structures are impressive materials with a promising outlook for future studies and applications.
Citation
Eaton, A. (2024). Interface, Thermal, and Mechanical Properties of Multidimensional Carbon-Based Nanomaterials. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5583
