Elucidating the Interfacial Molecular Interaction Mechanisms of Silicone Adhesive, Polymer Degradation and Polymer Bio-applications Using Advanced Spectroscopy

Abstract

This thesis examines the use of Sum Frequency Generation (SFG) vibrational spectroscopy in studying buried polymer interfaces such as in silicone adhesives, which is crucial in understanding the molecular processes of polymer adhesion. Investigating these interfaces non-destructively has been challenging, and this work present insights into the molecular adhesion mechanisms of High-temperature vulcanized (HTV) silicone. HTV silicone, one of the most commonly used silicone, is based on the hydrosilylation curing chemistry. The study also considers the effects of various additives, such as adhesion promoters, fillers, and catalysts on the buried interfacial structure.

Silicone matrices were examined to see how different compositions affected adhesion. Findings show that the addition of fillers reduce the interfacial segregation of the adhesion promoter but increased the strength of adhesion when a catalyst is added. For the first time, interfacial chemical reactions between HTV silicone and polar polymer substrates were directly monitored using SFG, demonstrating the amplification of silicone adhesion through adhesion promoter characteristics, surface composition and interfacial reaction.

In addition, the molecular interactions between biological molecules and polymer surfaces in situ were studied, identifying that the charge-charge interaction was the dominant interaction at the interface, which outperformed the π–π interaction.

The degradation mechanisms of polyethylene, an environmental concern due to its increasing accumulation, were also explored, focusing on understanding its behavior in the environment and its degradation mechanisms after exposure to UV irradiation. This knowledge can help develop strategies to mitigate the impact of degraded materials.