Sorption, swelling, and free volume of polybenzimidazole (PBI) and PBI/zeolitic imidazolate framework (ZIF-8) nano-composite membranes for pervaporation

• Published in: Polymer (Guilford) Vol. 54; no. 2; pp. 774 - 783
• Main Authors: Shi, Gui Min, Chen, Hongmin, Jean, Y.C., Chung, Tai Shung
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 24.01.2013; Elsevier
• Subjects: Applied sciences; Composites; diffusivity; ethanol; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Free volume; hydrophobicity; methanol; Nano-composite membranes; permeability; Pervaporation; Polymer industry, paints, wood; polymers; sorption; spectroscopy; Technology of polymers; Free volume; Nano-composite membranes; Pervaporation; Water; Imidazole derivatives; Transport properties; Ethanol; Zinc complex; Volatile organic compound; Experimental study; Benzimidazole copolymer; Sorption; Aromatic copolymer; Membrane; Nanocomposite; Kinetics; Phenylene copolymer
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2012.11.056

We have studied alcohol- and water-induced swelling and sorption of PBI and PBI/ZIF-8 nano-composite membranes and characterized both dry and wet membranes by positron annihilation lifetime spectroscopy (PALS). The degrees of membrane swelling after immersing in alcohols and water follow the order of ethanol > methanol > water > n-butanol. Addition of ZIF-8 particles into PBI membranes suppresses the ethanol-, methanol- and water-induced PBI swelling. The water-induced swelling is subdued most severely because of the hydrophobic nature and rigid structure of ZIF-8 particles, while the n-butanol-induced swelling is enhanced owing to a greater free volume in the PBI/ZIF-8 membrane. The PALS studies confirm that the high pervaporation permeability of PBI/ZIF-8 membranes is attributed to the high fractional free volume (FFV) created by large cavities of ZIF-8 particles. In addition, the alcohol saturated PBI/ZIF-8 membranes have significantly smaller free volume radii than alcohol saturated PBI membranes. A correlation among FFV, pervaporation permeability and sorption diffusion coefficient has been developed. This study also demonstrates the importance of using PALS to characterize membrane structure changes in solvent-saturated membranes at a molecular level and to correlate pervaporation performance with solvent-induced swelling. [Display omitted]