CBE Doctoral Dissertation Defense: “Leveraging confinement and surface effects to control polymer phase behavior and transport phenomena in polymer-infiltrated nanoparticle films” (Trevor Devine)

Highly loaded, polymer-infiltrated nanoparticle films (PINFs) enable the synergistic combination of polymers with the functionality of nanoscale fillers. Extensive studies have found that their behavior deviates markedly from bulk polymers due to extreme confinement and high interfacial area within the interstitial pore network. However, incorporating polymer blends in these PINFs (blend-PINFs) is unexplored. Confinement and nanoparticle surface interactions may substantially alter phase behavior from bulk expectations. Additionally, the prevalence of adsorbed polymer layers within PINFs present an opportunity to engineer a polymeric material dominated by interfacial effects, with little or no bulk region. In this thesis, we investigate how confinement and polymer-nanoparticle interaction asymmetry impact phase behavior, solvent resistance, and transport phenomena in blend-PINFs. Using a combination of optical microscopy, spectroscopic ellipsometry, scanning electron microscopy, small-angle neutron scattering (SANS), and resonant soft X-ray scattering (RSoXS), we examine how blend morphology deviates under nanoconfinement. To probe solvent resistance, we employ ex situ solvation experiments to track polymer removal and determine how confinement and surface chemistry influence polymer retention. We also introduce a novel fabrication method, Sequential Capillary Rise Infiltration (SCaRI), which sequentially infiltrates individual polymers. We find that strong asymmetry in polymer-nanoparticle interactions can suppress macroscopic phase separation by inducing pore-scale segregation. In blends with symmetric interactions, confinement produces more complex, system-specific effects, leading to either compatibilization or phase separation depending on blend type. We find that confinement enhances solvent resistance in PINFs, but surprisingly, resistance is not governed solely by polymer-solvent interactions: solvent-nanoparticle interactions emerge as a dominant factor in displacing adsorbed chains. Through SCaRI, we demonstrate that the infiltration sequence can significantly alter the final infiltration amount, and that phase morphology resembles fully infiltrated, CaRI-produced structures only when the second polymer has a stronger nanoparticle affinity. Overall, our results reveal several fundamental findings that allow more intelligent design of PINF and blend-PINFs that synergistical combine the aspects of its constituent polymers and nanoparticles, while also unlocking novel properties unachievable without the highly loaded nature of the PINFs.