Dependence of Solvents and Surface Effects on Metal-Organic Framework Polymer Chain Interpenetration and Interfacial Stability.

Abstract

Polymer-based coatings often incorporate fillers or inclusions into the polymer matrix to tune application-specific physical and chemical properties. Furthermore, the presence of specific solvents can either promote or impede dispersal of the inclusions and polymer chains. Here, all-atom molecular dynamics (MD) simulations are performed to probe the formation of interfacial regions in metal-organic framework (MOF)-polymer composites by including nanoscale crystallites of UiO-66 in a binder of a polyurethane or polyhydroxyurethane solvated with hexane or hexanol. We study the effect of different surface chemistries on the metal oxide nodes (hydroxyl, formate, or acetate groups), calculating polymer and solvent 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 interfacial uniformity. The simulations show that chain penetration into the MOF can be either entirely impeded by the choice of the blending solvent or promoted by the particular surface functionalization. Energetic barriers from the MD are directly extracted to quantify chain interpenetration of the MOF and reveal that interpenetration is a stabilizing process during interface formation and strongly dependent upon solvent presence and surface chemistry.