Revealing the Transient Concentration of CO₂ in a Mixed‐Matrix Membrane by IR Microimaging and Molecular Modeling

Abstract

Through IR microimaging the spatially and temporally resolved development of the CO concentration in a ZIF-8@6FDA-DAM mixed matrix membrane (MMM) was visualized during transient adsorption. By recording the evolution of the CO concentration, it is observed that the CO molecules propagate from the ZIF-8 filler, which acts as a transport "highway", towards the surrounding polymer. A high-CO -concentration layer is formed at the MOF/polymer interface, which becomes more pronounced at higher CO gas pressures. A microscopic explanation of the origins of this phenomenon is suggested by means of molecular modeling. By applying a computational methodology combining quantum and force-field based calculations, the formation of microvoids at the MOF/polymer interface is predicted. Grand canonical Monte Carlo simulations further demonstrate that CO tends to preferentially reside in these microvoids, which is expected to facilitate CO accumulation at the interface.

Molecular Modeling Investigations of Sorption and Diffusion of Small Molecules in Glassy Polymers

“…In terms of molecular simulation, for the reliable prediction of properties and the fundamental understanding of the underlying mechanisms in complex and multicomponent materials, it is crucial that the existing hierarchical methods, described in the previous sections, be extended and generalized so that they can be implemented in a straightforward manner. Additionally, unravelling the interfacial interactions [287,288] and characteristics [289,290,291] in polymer-based composite materials is of great importance for an accurate description of their behavior. Development and implementation of efficient, hybrid and adaptive resolution multiscale molecular simulation methods [125,292,293,294,295,296,297,298] may in many cases be necessary for the systematic study of microscopic behavior at the interfaces in composite materials and mixed matrix membranes and for further advancement of the materials-by-design target.…”

Diffusion in nanopores: correlating experimental findings with “first-principles” predictions

“…If they are not properly taken into account, the measurements can give rise to completely wrong conclusions about the underlying diffusion phenomena. Their detection has remained a challenging task until today, notably on considering heterogeneous systems like mixed matrix membranes (Mueller et al 2015;Friebe et al 2017;Dutta and Bhatia 2018;Hwang et al 2018;Forman et al 2019).…”

Application of microimaging to diffusion studies in nanoporous materials

“…This experimental finding nicely corroborates with predictions of grand canonical Monte Carlo simulations (Semino et al 2016) that polymer micro-voids, which Reprinted from ref. (Hwang et al 2018) with permission may be expected to occur predominantly in the vicinity of the interface between the MOF crystal and the polymer bulk phase, give rise to an accumulation of the CO 2 molecules (Hwang et al 2018).…”