Event Type:
MSE Grad Presentation
Talk Title:
Vapor Phase Infiltration of Titanium Tetrachloride into Polymers with Ester Functional Groups
MRDC Classroom 3403 and Virtually via Zoom

            Prof. Mark D. Losego – School of Material Science & Engineering (advisor)
            Prof. Guoxiang (Emma) Hu – School of Material Science & Engineering
            Prof. Juan-Pablo Correa-Baena – School of Material Science & Engineering
            Prof. Andrew J. Medford – School of Chemical & Biomolecular Engineering
            Prof. Michael Filler – School of Chemical & Biomolecular Engineering

Vapor phase infiltration (VPI) is a technique that infuses metal oxides into polymers, forming hybrid materials with novel properties, structures, and functionalities. Recent advancements in VPI have significantly enhanced our understanding of the fundamental kinetics, thermodynamics, and chemistry underlying this process. However, these advancements have predominantly focused on specific polymer and precursor chemistries, such as TMA/PMMA. To further advance the field of VPI, it is essential to explore additional precursor/chemistry combinations to achieve a more comprehensive understanding of VPI mechanisms.

This thesis aims to expand our knowledge of VPI by investigating the infiltration of TiCl4 into polymers containing ester functional groups, such as PMMA and PLA, aiming to deepen our comprehension of the fundamental kinetics, chemistry, and thermodynamics of this process. Previous studies have limited their focus to certain polymer and precursor chemistries, such as TMA/PMMA. The research presented in this thesis aims to provide a comprehensive insight into the TiCl4/polymer systems by comparing them with existing precursor/polymer systems.

The investigation begins with an analysis of the kinetics of TiCl4 infiltration into PMMA and PLA, identifying the rate-limiting steps and comparing these to the TMA/PMMA system. This involves acquiring XPS depth profiles and applying a reaction-diffusion model to understand the influence of the Damköhler number and non-Fickian diffusion processes on inorganic concentration profiles within the polymer matrix. Findings suggest that TiCl4 infiltration is primarily reaction-limited in both polymers, contrasting with the predominantly diffusion-limited process observed in lower temperatures for TMA/PMMA systems.

Chemically, TiCl4 interacts with PMMA and PLA through a dealkylation mechanism, leading to a primary bond formation between the organic and inorganic components and the generation of chloromethane byproducts. This process is confirmed through XPS, FTIR spectroscopy, and in-situ QCM analyses, which also demonstrate the formation of inorganic cross-links in the resulting TiOx-PMMA hybrid materials. For PLA, similar reactions cause polymer chain scission and depolymerization, suggesting potential uses of VPI as a subtractive manufacturing process.

Thermodynamically, the activation energy for effective diffusivity was calculated using initial mass uptake data, showing negative values indicative of complex sorption and diffusion dynamics. The reaction-diffusion model helps further elucidate how sorption is the predominant factor affecting the TiCl4 infiltration process in PMMA, whereas rapid polymer degradation in PLA limits detailed thermodynamic analysis.

In conclusion, this thesis significantly advances the field of VPI by delineating the intricate relationships between chemical reactions, material transformations, and thermodynamic constraints in the TiCl4 infiltration of ester-containing polymers. The findings not only broaden the application spectrum of VPI but also enhance the understanding of fundamental materials science principles involved in polymer-inorganic hybrid material formation.