Theses and Dissertations

Date of Award

7-1-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Karen S. Martirosyan

Second Advisor

Ahmed Touhami

Third Advisor

Mircea Chipara

Abstract

Carbon nanotubes (CNTs) possess exceptional mechanical strength, electrical conductivity, thermal stability, and low density, making them attractive building blocks for multifunctional materials. However, translating these remarkable nanoscale properties into macroscopic systems remains challenging because of weak interfacial interactions, inefficient load transfer, and structural heterogeneity. This dissertation addresses these challenges through the development of carbon-based nanocomposites that integrate ceramic reinforcement, polymer-derived ceramic conversion, and metallic nanoparticle functionalization to enhance both structural performance and sensing capability.

Three complementary approaches were investigated to engineer multifunctional CNT-based systems. The first focused on the fabrication of titanium carbide (TiC)-reinforced CNT yarns through in situ exothermic combustion synthesis. The Ti–C reaction promoted TiC formation throughout the CNT architecture, creating ceramic bridges between neighboring nanotubes that strengthened interfacial bonding and enhanced load transfer, resulting in improved structural integrity and multifunctional performance.

The second approach investigated polymer-derived ceramic conversion using polycarbosilane (PCS) as a precursor for silicon carbide (SiC) formation within CNT yarns. Conventional thermal processing and Joule heating were employed to study the polymer-to-ceramic transformation and its influence on material properties. The results demonstrated that controlled ceramic conversion could be achieved while preserving the integrity of the CNT framework, improving thermal stability and structural robustness.

The third approach focused on the development of flexible Ag-functionalized CNT sheets for room-temperature carbon monoxide (CO) sensing. Acid functionalization promoted uniform silver nanoparticle anchoring within the conductive CNT network. The resulting hybrid sensors exhibited reproducible and reversible electrical responses to CO under ambient conditions, demonstrating the feasibility of low-power chemiresistive sensing.

Overall, this work demonstrates that in situ ceramic formation, polymer-derived ceramic processing, and nanoparticle functionalization provide versatile and scalable strategies for engineering multifunctional CNT architectures with enhanced mechanical, thermal, electrical, thermoelectric, and sensing performance. By integrating structural reinforcement with functional response in a lightweight material platform, this dissertation establishes a framework for the design of advanced carbon-based nanocomposites with potential applications in aerospace, smart infrastructure, environmental monitoring, flexible electronics, energy systems, and advanced sensing technologies.

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Copyright 2026 Sara Sharifi. All Rights Reserved. https://proquest.com/docview/3408953636

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