Solvation and Surface Effects in MOF-Polymer Interfaces

Polymer-based coatings often incorporate fillers or inclusions into the polymer matrix to tune application-specific physical and chemical properties. The interactions between the polymer and the inclusion can strongly influence the formation of interfacial regions with local properties that may differ substantially from the bulk polymer. These regions in turn affect the material’s composite thermomechanical and transport behavior. In the case of inclusions that are porous such as metal-organic framework (MOF) particles, the presence of pores and specific surface termini that can vary likewise introduce further interfacial effects. Here, all-atom molecular dynamics (MD) simulations are performed to probe the formation of interfacial regions in MOF-polymer composites by including nanoscale crystallites of UiO-66 in a binder of polyurethane or polyhydroxyurethane solvated with hexane or hexanol. We parametrically study the effect of different surface chemistries on the metal oxide nodes (hydroxyl, formate, or acetate groups). For each combination we calculate local densities and interaction energies. We report secondary trends in chain adsorption (depletion) near the MOF surface as a function of different surface chemistries, while the polymer-solvent and solvent-solvent interactions appear as the primary factors controlling the uniformity of the interface. Additional temperature-accelerated simulations reveal that chain penetration into the MOF can be either entirely impeded by the choice of the blending solvent, or promoted (curtailed) by the particular surface functionalization.

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