PhD Oral Exam - Bianca Martins de Lima, Chemical and Materials 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

Polymeric thin films, exhibiting unique optical, electrical, and mechanical properties, can be engineered for various technologies, including adhesives, membranes, optical systems, and electronics. The interfacial region between these films and their environment plays a crucial role in key processes such as nucleation, crystallization, adhesion, and wettability. The conformation of polymer chains near the interface significantly influences these processes. However, there is lack of studies that establish clear correlations between interfacial chain conformation and the macroscopic behavior of thin films. In this study, we employed Sum Frequency Generation (SFG) spectroscopy to investigate the interfacial conformation of polystyrene chains across various systems, establishing valuable relationships between substrate properties, interfacial chain conformation, and macroscopic thin film properties.

First, we examined the role of the polymer molecular weight in driving interfacial chain conformation. We found significant differences in the conformation of polystyrene chains near a metallic substrate, depending on the polymer molecular weight. Our analysis revealed that the balance between entropy and enthalpy during polymer adsorption plays a crucial role in determining the chain conformation.

Building on the previous findings, we explored the relationship between the polymer molecular weight, the interfacial environment (free and buried interfaces), the chain conformation and the dewetting behavior of thin films. Our study revealed that polystyrene chains of the same molecular weight adopt distinct conformations depending on the interface and that these differences in chain conformation play a key role in determining the dewetting behavior of thin films.

Lastly, we conducted a pioneering work demonstrating the potential use of SFG spectroscopy to determine the lamellar orientation at the surface of semi-crystalline thin films. This study broadens the scope of SFG spectroscopy and expands the range of analytical tools available for interfacial lamellar orientation analysis, particularly in complex systems, such as at buried interfaces.

This work provides valuable insights that enhance the fundamental understanding of interfacial properties, chain conformations, and the macroscopic behavior of thin films. By integrating innovative SFG spectroscopy applications with theoretical calculations, we have established a robust foundation for future studies in polymer science and materials engineering, driving advancements in thin film technologies and applications.