PhD Oral Exam - Ghazaleh Ramezani, Mechanical Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This thesis addresses the critical need for sustainable, high-performance materials by exploring eco-friendly nanocomposites composed of graphene oxide (GO) and reduced graphene oxide (rGO) within a nanocellulose matrix. Nanocellulose, in the from of cellulose nanocrystals and nanofibers, is preferred due to its nanoscale dimensions that provide a high surface area, enhanced flexibility, and superior mechanical and chemical reactivity, making it an ideal matrix for integrating functional nanomaterials. GO and rGO complement each other: GO’s oxygen-containing groups facilitate surface modification and dispersion in aqueous media, while rGO restores electrical conductivity necessary for biosensing and flexible electronics. In this work, GO and rGO were synthesized and reduced using green agents like citric and L-ascorbic acids, offering scalable and safer alternatives to conventional methods.

Experimental studies on nanocellulose/GO and nanocellulose/rGO films demonstrated exceptional electrical conductivity, mechanical strength, and environmental stability, vital for wearable electronics and biosensors. Spectroscopic, microscopic, and electrochemical analyses revealed the roles of hydrogen bonding, π–π interactions, and composite architecture in performance. Predictive modeling using Lasso regression and neural networks established robust composition–property relationships with high accuracy (R² > 0.99).

Overall, this research confirms that nanocellulose composites with GO and rGO are renewable, recyclable, and functional under ambient conditions, presenting promising applications in biosensing, smart packaging, and health monitoring. The study advances our understanding of why nanocellulose and GO/rGO-based hybrids are uniquely suited, fostering progress in sustainable functional materials at the nanoscale.