Correlating Gas Permeability and Young’s Modulus during the Physical Aging of Polymers of Intrinsic Microporosity Using Atomic Force Microscopy

Abstract

The relationship, during physical aging, between the transport properties and Young's modulus for films of polymers of intrinsic microporosity (PIM) was investigated using pure gas permeability and atomic force microscopy (AFM) in force spectroscopy mode. Excellent agreement of Young's modulus measured for the archetypal PIM-1 with values obtained by other techniques in the literature, confirms the suitability of AFM force spectroscopy for the rapid and convenient assessment of mechanical properties. Results from different polymers including PIM-1 and five ultrapermeable benzotriptycene-based PIMs provide direct evidence that size selectivity is strongly correlated to Young's modulus. In addition, film samples of one representative PIM (PIM-DTFM-BTrip) were subjected to both normal physical aging and to accelerated aging by thermal conditioning under vacuum for comparison. Accelerated aging resulted in a similar decrease in permeability and increase in Young's modulus as normal aging, however, significant differences suggest that thermally induced accelerated aging occurs throughout the bulk of the polymer film whereas normal aging occurs predominantly at the surface of the film. For all PIMs, the increased in film rigidity upon aging led to an increase in gas size selectivity.

Sulfonyl PIM‐1: A diverse separation membrane with dilation resistance

“…However, the conceived adsorbent may display mechanical weakness and tend to excessively swell/plasticize, which is prohibitive for practical adsorption applications. This can be further placed in connection with recent work by Longo et al 64 that observed correlated behavior between Young's modulus and the mass transport properties of six different tested PIMs. In this context, it is understood that various adsorbent material properties can be interconnected and as a result provide additional levels of complexity to the adsorbent design process.…”

Physical Aging Behavior of a Glassy Polyether

“…Indeed, volume shrinkage could be detrimental for the glass lifetime [ 9 ]; therefore, aging must be by glass manufacturers to avoid any undesired alteration of properties over the course of time. Notable examples in this sense are those on the effect of aging on gas transport properties [ 10 , 11 , 12 , 13 ] also in relation to mechanical properties [ 14 ]. The relation between gas transport properties and the thermodynamic state of the glass has also been discussed [ 15 ].…”

Ultrapermeable Polymers of Intrinsic Microporosity Containing Spirocyclic Units with Fused Triptycenes

“…For comparison, the data measured under the same conditions by Longo et al for PIM‐1 after MeOH treatment (○) and 2219 days of ageing (◆) are indicated in green. [ 22 ] Other literature data are reported in grey symbols for PIM‐1 (+), SBF‐based PIMs (O), ultrapermeable triptycene based PIMs () and PTMSP (×).…”