Modeling water diffusion in polybenzimidazole membranes using partial immobilization and free volume theory

POLYMER

卷:189

Article

Moon, Joshua D.¹  Galizia, Michele²  Borjigin, Hailun³  Liu, Ran³  Riffle, Judy S.³  Freeman, Benny D.⁴  Paul, Donald R.⁴ 

[1] Univ Calif Santa Barbara, Calif NanoSyst Inst, Elings Hall,Mesa Rd, Santa Barbara, CA 93106 USA

[2] Univ Oklahoma, Sch Chem Biol & Mat Engn, 100 E Boyd St, Norman, OK 73019 USA

[3] Virginia Tech, Dept Chem, Macromol Innovat Inst, Blacksburg, VA 24061 USA

[4] Univ Texas Austin, John J McKetta Jr Dept Chem Engn, 2501 Speedway, Austin, TX 78712 USA

关键词: Diffusion;    Plasticization;    Free volume;    Partial immobilization;    Polybenzimidazole;   

DOI  :  10.1016/j.polymer.2020.122170

来源: Elsevier

【 摘 要 】

This study extends previous work on modeling water sorption, dilation, and diffusion in polybenzimidazoles (PBIs) by comparing water transport properties of commercial PBI (Celazole (R)) with three sulfone-containing PBIs. A model is developed combining free volume and partial immobilization theories to describe water diffusion coefficients across a wide range of concentrations and degrees of swelling. Water vapor sorption and dilation follow dual-mode behavior and generally correlate with the availability of strong hydrogen bonding sites on the polymer chains. At low concentrations, water diffusion coefficients are suppressed by partial immobilization of Langmuir species, while at high concentrations, water diffusion coefficients increase due to significant swelling and plasticization. To account for the influence of plasticization on free volume and water mobility, local Henry's law mobility coefficients are correlated with fractional free volume (FFV), where the volume occupied by water molecules is considered to contribute to dynamic free volume and is assumed to be as accessible for water diffusion as unoccupied free volume. Contributions to diffusion coefficients from thermodynamic and convective frame of reference effects and concentration averaging are also considered.

【 授权许可】

Free