Physical aging of polymers of intrinsic microporosity: a SAXS/WAXS study

Abstract

X-ray scattering patterns from these high free-volume polymeric glasses contain a feature strongly associated with porosity; it is sensitive to time, temperature and film thickness in a manner consistent with physical aging, which impacts membrane performance in gas separations.

Aging of polymers of intrinsic microporosity tracked by methanol vapour permeation

“…Furthermore, theoretical computation methods [13] were reported as well. However, only a few of the aforementioned studies mention the aging phenomenon in PIMs [9][10][11][12]. Moreover, to the best of our knowledge, there are neither studies about the nature (chemical or physical) of aging of PIMs, nor on the influences of the permeating compounds.…”

“…To explore the aging phenomenon, various authors use different methods to monitor the aging of polymeric membranes. Some studies were focused on changes in the physical structures of polymers, detected using SAXS/WAXS [12] or PALS [9,30], while others were focused on the influence of aging on the permeability [10,11,[30][31][32]. Furthermore, theoretical computation methods [13] were reported as well.…”

“…For example, their transient sorption kinetics cannot be described by the commonly used Fick's second law of diffusion. The second problem is the aging phenomenon [8], which causes a significant decrease of PIMs permeability over time [3,6,[9][10][11][12][13].…”

“…In this work, PIM-1 [3] and PIM-EA-TB [5] (see Figure 1) were chosen from the family of polymers of intrinsic microporosity. PIM-1 is an archetypal polymer, which was the first prepared PIM and is currently the most studied one [3,7,[9][10][11][12][33][34][35]. PIM-EA-TB was chosen because of its unique properties, especially for its gas separation ability [5].…”

Combining theory and experiment for X-ray absorption spectroscopy and resonant X-ray scattering characterization of polymers

“…Essentially, the neat polymer comprises the matrix and provides mechanical integrity to the membrane, while the 'unoccupied' volume that arises from imperfect packing of rigid polymer backbones serves as the 'highways' for transport of ions, gas, or water, depending on the chemistry of the polymer. One time-dependent study using small angle (SAXS) and wide angle Xray scattering (WAXS) and molecular dynamics (MD) simulations probes the dynamics of aging in microporous polymers with pore size <1 nm [142]. Physical aging is relevant because the closing of pores via this mechanism can drastically reduce molecular transport.…”