Polymer Molecular Weight as a Tuning Parameter for Enhancing CO2 Separation Performance in Supported Ionic Liquid Membranes

The molecular weight (MW) of polymers is among the parameters defining the self-organization of polymeric mixtures and complex fluids. Herein, we investigated the role of the MW of the support, poly(vinylidene fluoride) (PVDF), on CO₂ sorption and permeation within supported ionic liquid membranes (SILMs), prepared from a mixture of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][Tf2N]) and PVDF. We demonstrate direct correlations between polymer MW, crystallinity, morphology, and CO₂ interaction dynamics. It is noted that the use of low MW PVDF significantly enhances the CO₂ sorption capacity of the prepared SILMs, reaching three-fold higher values when compared with that of the free IL. Additionally, morphological analysis reveals that a 1:1 polymer-to-ionic liquid mass ratio (i.e., 50 wt % IL) facilitates the formation of the β-phase of PVDF, a polymorph with superior CO₂ affinity. The gas transport properties of the films are studied, and a CO₂ permeability of 22,100 ± 3110 barrer and a CO₂/N₂ ideal selectivity of 16 are measured.