(181q) Differentiating Free Diffusing from Reacted Species in Vapor Phase Infiltration
AIChE Annual Meeting
2024
2024 AIChE Annual Meeting
Materials Engineering and Sciences Division
Poster Session: Materials Engineering & Sciences (08F - Composite Materials)
Monday, October 28, 2024 - 3:30pm to 5:00pm
Vapor phase infiltration (VPI) transforms polymers into organic-inorganic hybrid materials by infusing the bulk of polymer prefactors with vapor phase metalorganic precursors and co-reacting to form air-stable hybrids. Due to the prevalence of reactions between the precursors and the polymers, the material properties of these hybrids are often different from the simple combination of the polymer and the inorganic. These hybrid materials have demonstrated wide applicability from providing solvent stability to membranes for chemical separations to evoking photoluminescence in fabrics. However, the fundamental transport and thermodynamic principles of this process are still emerging. In some systems, the vapor-phase precursors that infiltrate the polymer can exist as freely diffusing (or âdissolvedâ) species within the polymer, as species reversibly interacting with polymer functional groups, and as species that are irreversibly chemically reacted to the polymer. In this presentation, we combine physical experiments with phenomenological modeling to clearly delineate the fraction of species chemically reacted versus diffusing or weakly bound as a function of infiltration time and temperature for the infiltration of poly(methyl methacrylate) (PMMA) with trimethylaluminum (TMA). Quartz crystal microbalance gravimetry is used to track metalorganic precursor uptake and loss over extended sorption and desorption times to quantify equilibrium concentrations of free diffusing and weakly bound species versus reacted species. Delineating these two types of species reveals that the fraction of diffusing and weakly bound species at effective equilibrium (17 hours exposure of a 500 nm film) continuously decreases with VPI process temperature while the reacted species increase and eventually reach a saturation plateau with process temperature. The continuous decrease in diffusing and weakly bound species is explored through a vanât Hoff analysis of the Henryâs law solubility coefficient uncovering an exothermic heat of solution that varies with temperature regime. Diffusion coefficients, hindering factors, and reaction rates are extracted at each temperature using a previously established reaction-diffusion transport model and Bayesian optimization. While diffusion coefficients and the hindering factor do not vary significantly with temperature, the reaction rate shows a significant temperature dependency which is explored via Arrhenius analysis. Overall, this work provides fundamental insight into the thermodynamic and kinetic behaviors of VPI for the TMA / PMMA system and provides a framework for study in additional systems.
Figure 1. (a) Representative in situ quartz crystal microbalance gravimetry data showing the normalized mass change (normalized to polymer mass) as a function of time and processing step in the vapor phase infiltration of a 500 nm PMMA film with TMA and water at 130 ËC. (b) Average normalized total mass uptake of TMA during exposure (total sorbed, blue squares), mass remaining following desorption (bound, purple circles), and mass desorbed (turquoise triangles) as a function of infiltration temperature.