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

Mariagiulia Longo,Mariolino Carta,Elisa Esposito,Ian Rose,Maria Penelope De Santo,Alessio Fuoco,Marcello Monteleone,Bibiana Comesaña-Gándara,Neil B Mckeown,C Grazia Bezzu,Lidietta Giorno,Jie Chen,Johannes C Jansen

doi:10.1021/acs.iecr.9b04881

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.

Highlights

This design strategy was consistent with the structure of the first Polymer of Intrinsic Microporosity (PIM-1) in 2004,8 and led to successive modifications, including those containing rigid bridged bicyclic units such as Tröger’s base
The 3D histogram in Figure 2a shows the frequency distribution for ca. 60 individual measurements of Young’s modulus of a polymers of intrinsic microporosity (PIM)-1 film soaked in methanol and thermally treated or aged
Permeation tests and atomic force microscopy (AFM) force spectroscopy studies on a series of different PIM membranes revealed a strong correlation between the transport parameters and the polymer film stiffness

Summary

Introduction

The key to boost the use of membrane technology in these large-scale applications is the development of novel performing materials with improved permeability (productivity) and selectivity (purity of the products).. Freeman et al suggested that improvements in the performance of gas separation membranes require the synthesis of novel polymers with a simultaneous increase of chain stiffness and interchain separation.. Freeman et al suggested that improvements in the performance of gas separation membranes require the synthesis of novel polymers with a simultaneous increase of chain stiffness and interchain separation.7 This design strategy was consistent with the structure of the first Polymer of Intrinsic Microporosity (PIM-1) in 2004,8 and led to successive modifications, including those containing rigid bridged bicyclic units such as Tröger’s base..

Objectives

Results

Conclusion