Molecular engineering and nanostructuring of polymer networks for high performance gas separation membranes

Abstract

The architecturing and characterization of polymer-based materials at a molecular scale are of great importance in the development of novel rigid polymeric molecular sieves for high performance gas separation membranes. The new rapidly growing field of nanoscience technologies and material nanostructuring offers novel ways for creating nanoengineered material combinations. Intermolecular and supramolecular interactions among different molecules and clusters play an important role in the microscopic behavior of molecular architectures and molecular self-assembly. In this work, the coordination shell number of polyetherimide (PEI) membranes was determined from experimental X-ray diffraction data and found to be a key link between microscopic pair intermolecular interactions and macroscopic scale interactions. This link enabled us to determine the intermolecular force parameters required to understand material structuring at a molecular scale. These physical parameters are required in all models used in the determination of the micropore size distributions from gas adsorption isotherms. Computational chemistry and physicochemical principles were useful to illustrate molecular architecturing and coordinating to form intermediate stable molecular complexes during membrane fabrication. These coordination complexes acted as pore forming templates that could be disrupted and removed after polymer coagulation to open the closed PEI network structure and increase the interconnectivity and accessibility among polymer micropores. Based on nanotechnology concepts, a uniform dispersion of nanoscopically-sized filler particles into a polymer network created novel materials with superior properties and characteristics attributed to the presence of ultra-large interfacial area per unit volume. The adhesive (noncovalent interactions among different molecules) properties of nanoelement surfaces and polymer surfaces were the key for the creation of uniform polymeric molecular sieves. Narrowing the micropore size distribution is also possible when the adhesive energy between nanoparticles and polymer phase exceeds the cohesive energy of the pure polymer. Membranes were prepared using twelve metal-ligand complexes as filler additives that were uniformly dispersed into the PEI polymer solution before membrane casting. Membranes containing cobalt phthalocyanine (CoPc) showed the highest performance for oxygen separation from air. However, the performance was largely decreased upon annealing indicating a low nanostructure stability. (Abstract shortened by UMI.)