Computational studies of graphene and single walled carbon nanotube growth and carbonaceous polymeric nanocomposites
Graphene and single walled carbon nanotube (SWNT) has attracted a lot of attention in different fields of science due to its unique electrical, mechanical, and optical properties. Controlling the growth of graphene and SWNT is a very topical subject and critical for producing material with desired properties since their properties are highly dependent on their atomic structure and it is often desirable that the material contains very few or (if possible) no defects.
There is great interest in using carbon nanotubes (CNTs) to design high performance materials, primarily due to their unique mechanical, electrical and thermal properties. These properties, as well as their light weight, make them suitable as reinforcement additives in polymeric nanocomposites. This includes composites of polyethylene (PE) and polyacrylonitrile (PAN), which are widely used in commercial applications.
In this thesis, density functional theory (DFT) and Monte Carlo (MC) simulations based on a tight binding (TB) model are used to study the growth of graphene in the absence of a catalyst, and compare this with the growth mechanism on a Ni(111) surface. The growth of defect-free graphene at the atomic level was simulated which allowed for the study of the mechanisms of defect formation and healing. The growth of SWNT is also studied using the same computational methods and the role of Ni in maintaining an open SWNT end was investigated.
A valid force field is selected to study the effect of SWNTs on the polymer morphology in large PE composite systems. The results show that the PE wrapped around the SWNT thereby increasing the radius of gyration of the PE. Interfacial shear strength, interfacial bonding energy and Young’s modulus is measured and results show that short SWNTs as reinforcement do not increase the Young’s modulus for the systems studied here, whereas longer, aligned SWNTs increased the Young’s modulus in the SWNT axial direction.
Interfacial properties in SWNT-PE and SWNT-PAN composites is studied. These properties are critical for the other nanocomposite properties, such as interfacial shear stress and load transfer from the polymer to the SWNT additives. The effect of functionalization of SWNT on the interfacial properties were compared with those obtained for non-functionalized SWNTs. The results emphasize the improvement of interfacial properties after functionalizing the SWNTs with carboxylic acid groups. In addition, the changes in properties such as the interfacial shear stress are larger for the polar PAN systems than for the PE systems.