Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Chemical and Biomolecular Engineering

First Advisor

Daeyeon Lee

Second Advisor

Kathleen J. Stebe

Abstract

Nanocomposite films containing a high volume fraction (> 50vol%) of nanoparticles (NPs) in a polymer matrix are promising for their functionality and use as structural coatings, and also provide a unique platform to understand polymer behavior under strong confinement. In this work, we present a one-step, room temperature method for the fabrication of such films through solvent-driven infiltration of polymer (SIP) into NP packings from a bilayer film composed of a densely packed layer of NPs atop a polymer film. Upon exposure to solvent vapor, capillary condensation occurs in the NP packing, leading to plasticization of the polymer layer and subsequent infiltration of polymer into the NP layer. Infiltration proceeds from a swollen polymer film into the highly confined interstitial voids of the NP packing, providing a novel system for the study of polymer solutions infiltrating into confinement.

We show that the extent of polymer infiltration depends on the quality of solvent, the extent of confinement, and polymer-NP interactions through experimental work and theoretical modelling. We find that decreasing solvent quality leads to less infiltration, but if given enough time to infiltrate, even slightly poor solvents (χ = 0.7) can lead to significant infiltration. The use of a slightly poor solvent enables SIP via liquid solvent annealing. We study the effect of confinement on SIP by varying polymer molecular weight and NP size. While the dynamics of infiltration during SIP are strongly dependent on confinement, the final extent of infiltration is not. This is attributed to changes in concentration regimes as infiltration proceeds, which lead to shifting characteristic length scales in the system over time. Finally, we probe the effect of polymer-NP interactions on the kinetics of confined polymer translocation through an entropic barrier and investigate how this effect varies with solvent quality and confinement. It is found that τ is strongly dependent on the strength of the polymer-wall interactions and shows a nonmonotic dependence with interaction strength which qualitatively agrees with the MD simulations. The SIP technique is a versatile and tunable method to fabricate high filler-fraction nanocomposite films of controlled porosity. This work aims to understand the mechanism of polymer infiltration during SIP, which provides insights into polymer solution behavior under strong nanoconfinement.

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