In order to understand and control the interfaces that arise in metal organic framework (MOF)-polymer composites, it is useful to have a measure of the degree of chemical affinity or compatibility between the MOF and polymer. We have used a Hansen solubility-based assessment involving probe solvents to determine the location of UiO-66-NH2, a stable and commonly studied zirconium-based MOF, in solubility space with respect to dispersion, polar, and hydrogen bonding interactions, i.e., δD, δP, δH, respectively. Time-dependent turbidity measurements for UiO-66-NH2 crystals mixed in solution were performed to determine rank ordering of the MOF compatibility with 20 different probe solvents. Higher turbidity is associated with a tendency for the MOF to remain dispersed in solution while lower turbidity corresponds to a greater likelihood of the MOF precipitating out. Rank ordering for groups of solvents with similar dispersed MOF turbidity trends was used in the estimation of UiO-66-NH2 Hansen solubility-inspired parameters via HSPiP software. Comparison of parameters for UiO-66-NH2 and polymers under consideration for composites, such as polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polystyrene (PS), and polyvinyl alcohol (PVA) allowed for a prediction of the degree of affinity or compatibility in a MOF-polymer composite via calculation of the relative energy difference (RED) in solubility space. The range and trend of RED values for the UiO-66-NH2-polymer combinations was then compared to variations in materials properties measured for thin films using dynamic mechanical analysis (DMA) and viscoelastic mapping of cross sectioned films using amplitude modulated and frequency modulated atomic force microscopy (AM-FM AFM). [Approved for Public Release: Distribution Unlimited]

Measurement of MOF-solvent interactions for assessment of compatibility and affinity in polymer matrices

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