How to Get the Best Gas Separation Membranes from State-of-the-Art Glassy Polymers

Herein we focus on fundamental polymer science factors in membrane-based gas separation to open another chapter on this important topic. Realistically thinking about nanometer and angstrom scale matrix attributes that are translatable into higher performance thin glassy polymer asymmetric membrane layers in practical large-scale devices is crucial. Such thinking should be guided by expertise in both polymer and membrane communities to advance the state-of-the-art. Polymer structures, membrane morphologies, and effects of operating conditions are discussed here by using specific examples to illustrate key issues. Rubbery polymers are not the focus of this discussion since they lack diffusive discrimination for size-similar penetrants, which glassy polymers provide and make them the focus here. Four scalable subtopics guide necessary thinking: (i) plasticization, (ii) antiplasticization, (iii) dual-mode transport involving saturation of unrelaxed free volume, and (iv) nonuniform free volume and stress profiles in thin skin glassy polymer asymmetric or composite membranes. Using these subtopics in the context of macromolecular science, we discuss issues needed to expand the state-of-the-art in gas separation membranes.