CBE Doctoral Dissertation: “Understanding and Controlling Polymer-Porous Solid Interactions for Catalytic Recycling of Polymers” (Tian Ren)

Understanding and controlling polymer-solid interactions is critical for optimizing the catalytic processes involved in polymer upcycling. In this Ph.D. thesis, I explored the intricacies of polymer behavior in nanoporous materials by monitoring the capillary infiltration dynamics of polystyrene (PS) and polyethylene (PE) into random packings of silica nanoparticles. To test the effect of surface chemistry without changing the structure and size of nanopores, these silica nanoparticle packings were modified with TiO 2 , WO 3 , and CaCO 3 using atomic layer deposition (ALD). Based on the Lucas-Washburn model, I quantified the polymer-porous solid interactions using contact angles and interfacial energies, finding a negative correlation between specific adsorption behaviors of small molecules and interfacial energies of polymers. Furthermore, I investigated the confinement effect, observing that the effective viscosity of polymer confined in sub-20 nm pores is inversely related to pore size. Changing the surface chemistry or polymer structure did not affect this inverse relationship, indicating the dominant role of physical confinement on the translational dynamics of PE. I also assessed the melting points of PE when confined within porous media. I observed a consistent decrease in the melting point as the pore size was reduced, down to a threshold of 11 nm. Below this size, the melting point stabilized and remained constant. These findings on the effect of surface chemistry and pore size on the dynamics and thermal properties of polymers potentially provide important insights and guidelines in designing efficient polymer upcycling reactions.