Carbon nanotubes (CNTs) possess extraordinary electrical properties including conductivity that is comparable to metals and breakdown current density that is orders of magnitude higher than copper. In order to take advantage of the electrical performance of CNTs in engineering applications, macroscopic carbon nanotube networks (NTN) are fabricated by entangling large amounts of CNTs into thin sheets. However, the electrical properties of these networks are much lower than those of individual nanotubes. Stretch-induced alignment of CNTs is an effective approach to enhance the electrical conductivity of the NTNs. However, the alignment mechanism of NTNs during the stretching process has not been fully investigated. This study employed in-situ X-ray and Raman scattering techniques to characterize the NTN structural evolution during stretch-induced alignment. The observed inhomogeneous alignment of NTNs prompts the need for a method that accurately determines the degree of nanotube alignment in bulk materials. A method that combines X-ray scattering and electrical anisotropy measurement was explored and proposed to determine the aligned fractions of nanotubes. Based on the characterization results, the structure-property relationship of NTNs and their electrical conductivity was studied through a 3D physics-based electrical model. The model was built in two stages. First, the structural model of NTNs was built using coarse-grained molecular dynamics, which provides high fidelity representation of the waviness, contacts and self-assembly of constituent nanotubes and ropes that originated from the van der Waals interactions. By applying tensile strains, the dynamics model also enabled the direct simulation of the dynamics of networks aligned through stretching. After the network structure was established, the simulated NTNs were translated into equivalent electrical circuits. The electrical model was developed based on the Simulation Program with Integrated Circuit Emphasis, which allows us to directly conduct device design and analysis using NTNs. This model is able to capture the effects of alignment and contact changes on the electrical properties of NTNs. Based on the understanding of the unique contact resistance dominated transport mechanism of NTNs, sensor applications of the novel materials were explored. By manipulating the tunneling barrier through either polymer molecule insertion or increasing the tunneling distances, NTNs were studied for potential applications in detecting organic solvent leakage and sensing tensile strains. Scaling-up of sensor fabrication using aligned NTNs and advanced printing technology was also explored and demonstrated. / A Dissertation submitted to the Department of Industrial and Manufacturing Engineering in partial fulfillment of the requirements for the degree of Doctor of
Philosophy. / Fall Semester, 2012. / November 2, 2012. / Includes bibliographical references. / Richard Liang, Professor Directing Thesis; Petru Andrei, University Representative; Arda Vanli, Committee Member; Chuck Zhang, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_183573 |
| Contributors | Li, Shu (authoraut), Liang, Richard (professor directing thesis), Andrei, Petru (university representative), Vanli, Arda (committee member), Zhang, Chuck (committee member), Department of Industrial and Manufacturing Engineering (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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