Interfacial Properties Determined By Molecular Simulation of Mixed-Matrix Membranes Containing Functionalized Metal-Organic Frameworks

Mixed matrix membranes (MMMs) containing metal organic frameworks (MOFs) are considered to be more promising materials for CO₂ capture compared to pure polymers or pure MOFs since it combines the advantages of a polymer matrix (easily processed) and MOFs (excellent gas transport performance). When there is poor binding between the polymer phase and MOF particles, interfacial properties can dominate the overall gas transport performance of these composite materials. Sometimes researchers can overcome this difficulty by pre-treating filler particles with polymer agents, or by adding functional groups to the filler particles that enhance binding with the polymer. However it is very difficult to directly characterize the fundamental properties of the interfacial region between the particle and the matrix using conventional characterization techniques because of the limited volume fraction of interface. Only bulk properties of the film can be measured practically, and SEM images reveal only limited information. Therefore it is of interest to more fully explore the interfacial binding using molecular simulations. In this work, force field parameters for MOF surfaces have been implemented using ab initio calculations. Then interfacial properties including binding energies of a single chain on MOF surfaces, exfoliation energies between polymer and MOF surfaces, and interfacial morphologies have been calculated using classical molecular dynamics. Our simulations indicate that polymer/neat MOFs have a tendency for poor binding. Therefore, a variety of functionalized MOFs have been designed and simulated in order to investigate the optimal structure for strong binding between the polymer matrix and MOF fillers.