Dielectric Analysis of Blended Polysulfone/Polyethylenimine Membrane Contactors for CO₂ Capture

Polysulfone membranes, used as contactors for CO₂ capture, are blended with two different hyperbranched polyethyleneimines modified with benzoyl chloride (Additive 1) and phenyl isocyanate (Additive 2) in different percentages. Fourier-transformed infrared spectra evidence the presence of urea and amide groups, whereas the field emission scanning electron microscopy images show differences in the microstructure of the blended membranes. Dielectric spectra determine the motions of the side and backbone chains, which can facilitate the diffusion of CO₂ . The spectra consist of six dielectric processes; three of them are due to the polysulfone (γ_PSf , β_PSf , and α_PSf ), whereas the rest are characteristic of the additive (γ_HPEI , β_HPEI , and α_HPEI ). The benzoyl chloride and phenyl isocyanate functional groups introduce variations in molecular mobility and modify the relaxations associated with the hyperbranched polyethyleneimine (HPEI). The additives also increase the conductivity of the blended membranes, which can compromise the performance of the membranes, specifically in the case of Additive 1. Ion hopping is found to be the prevailing charge transport mechanism while both relaxations, α_HPEI and α_PSf , are actives. These results, together with the final morphology of the membranes, may explain the greater absorption capacity of the membranes prepared with the hyperbranched polyethyleneimine modified with Additive 2.