Solvent Selection Guided by Self-Consistent Field Theory for Improved Dispersion of Metal–Organic Frameworks in Polymers

Abstract

Composite materials consisting of metal−organic frameworks (MOFs) in a polymer matrix require good dispersion of the MOF particles and compatibility of the polymer with the MOF to avoid interfacial defects. In the case of chemical permeability, poor MOF integration can result in nonselective transport pathways through the composite. Solubility parameters are widely used to predict the compatibility of various substances, including polymers, solvents, and solid inclusions. However, very little published solubility parameter data are available for MOFs. Here, the Hansen solubility parameters of the Zr-based MOF UiO-66-NH 2 are determined by dispersing the MOF in 15 different solvents and monitoring the turbidity of the suspensions over time. Application of solubility parameters alone to predict MOF dispersion in solution-processed polymer composites is not straightforward because it is difficult to resolve the three-way MOFpolymer-solvent interactions that can drive the particles from agglomerated to well-dispersed. Self-consistent field theory (SCFT) provides a quantitative framework for predicting the adsorption behavior of polymers on particles in solution and is employed here in conjunction with the determined solubility parameters for UiO-66-NH 2 to identify solvent blends for improved MOF dispersion in both polystyrene and poly(methyl methacrylate). Scanning electron microscopy shows improved dispersion of UiO-66-NH 2 in both polymers for the predicted solvent blends, demonstrating the utility of the proposed method.