Plasticization mechanism in polybenzimidazole membranes for organic solvent nanofiltration: Molecular insights from in situ FTIR spectroscopy

Abstract

Despite substantial research efforts being devoted to design polymer membranes for organic solvent nanofiltration (OSN) exhibiting enhanced plasticization resistance, detailed studies of membrane structural stability in chemically challenging environments are rare. This study sets forth a multiscale method, which combines in situ FTIR measurements in the transmission mode with sorption and transport measurements, to investigate the molecular mechanism of polymer plasticization upon exposure to organic species. We recently reported that polybenzimidazole (PBI), a polymer that has been considered for OSN application, experiences severe plasticization upon exposure to methanol. FTIR measurements suggest that the mechanism of PBI plasticization relies on competitive hydrogen bonding. According to this mechanism, methanol molecules disrupt the hydrogen bonded network characteristic of dry PBI, by forming mutual polymer/penetrant hydrogen bonds, which enhances polymer chain mobility and favors polymer plasticization. The analysis of the isosteric heat of sorption supports the picture sketched above. The method developed in this study can be readily extended to many other systems of practical interest in membrane science, to shed fundamental light on the phenomenon of plasticization, whose molecular aspects are still largely unknown. Equally important, this study provides some useful guidelines to design OSN membrane materials.

Molecular sieving using metal–polymer coordination membranes in organic media

“…This observations is in line with a previous report on PBI. 5 The XRD analysis revealed that the structure of the MPC membranes is dominated by amorphous characteristics (Fig. 2g).…”

“…Consequently, PBI has recently been explored for OSN. [1][2][3][4][5] Nevertheless, PBI membranes are not stable in harsh polar aprotic solvents without crosslinking.…”

Designing organic solvent separation membranes: polymers, porous structures, 2D materials, and their combinations

“…However, in contrast to permeance, permeability is an intrinsic membrane material property and, as such, it should be used to develop structure-property correlations instead of permeance. 14,58,[60][61][62] Based on the solution-diffusion model, the permeability of species i is given by: 14,58 (1) = × where is the diffusion coefficient and is the sorption coefficient. The membrane selectivity is the ratio of the permeability of the components i-to-j, and can be deconvoluted into the sorption and diffusion selectivity as follows:…”

Insight into the role of free volume in irradiation resistance to discoloration of lead‐containing plexiglass

“…The plasticization of polymer can reduce the interactions among polymer chains, increasing their mobility as a result. 38 Free volume theory is often employed to explain the plasticization mechanism. The larger the free volume, the better the mobility of polymer chain.…”