Understanding polymer-porous solid interactions based on small gas molecule adsorption behavior

Abstract

Understanding the interactions between molten polymers and inorganic porous solids is critical for the heterogeneous catalytic conversion of waste polymers into useful chemicals and the fabrication of nanocomposites and nanostructured polymers. Developing experimental and theoretical approaches to quantify and understand polymer-surface interactions would be extremely useful for the design of new catalysts and composites. Here, we demonstrate that the interfacial energy between molten polystyrene (PS) or polyethylene (PE) and various inorganic surfaces prepared via atomic layer deposition (ALD) such as SiO2, TiO2, WO3, and CaCO3 are correlated with the adsorption of small molecules that bear structural similarity to the repeat unit of the two polymers. The interfacial energy inferred from the dynamics of polymer infiltration into ALD-modified porous solids is compared with the heats of adsorption of small molecules on mesoporous silica (SBA-15) modified with ALD. Both our experimental and computational results suggest a strong correlation between the polymer-solid interfacial energy and the adsorption strengths of their respective small molecules on the same surface. These results highlight that even though there are no specific modes of interaction between the polymers and the inorganic surfaces, their interaction energies vary significantly and are dominated by differences in the enthalpic interactions between each repeat unit and the solid surface. Besides providing a novel method for measuring the polymer-solid interaction, this work bridges the gap between the behavior of macromolecules on solid surfaces and the adsorption properties of small gas molecules. This understanding will have important implications for designing new catalysts for polymer upcycling and composite membranes for gas and potentially polymer separation.