In situ monitoring of nonlinear physical aging and anti-aging in polymer-based separation membranes

Abstract

Glassy polymers are systems out of equilibrium, the theoretical description of physical aging effects on polymeric membranes for gas separation has thus far remained elusive. Herein, we introduce an in situ positron annihilation method combined with a series of time-dependent permeability for thermally rearranged polymer (TR-1), polymer with intrinsic microporosity (PIM-1), carbon molecular sieve (CMS) membrane and mixed matrix membrane (PIM-1-C, PIM-1+10wt% COF-316) during the aging process, to provide a fundamental micro-mechanism of relaxation and the form of expression for transport behavior. The challenging issues of accurate quantifying free volume and defining that in terms of measurable quantity have been addressed. The results indicate that the aging dynamics follow a stretched exponential decay function. Physical aging in PIM-1 differs from TR-1, as the different molding methods. Compared to semi-rigid polymer materials, CMS membranes exhibit the most demanding size-sensitive pairs due to their ultra-microporous structure during the densification process. The restricted diffusion of larger gases leads to irregular transport behavior, resulting in enhanced selectivity in aged membranes. Furthermore, a comprehensive understanding of the anti-aging process based on confinement effect is also monitored.