Polyimide-SiO2-TiO2 nanocomposite structural study probing free volume, physical properties, and gas transport

Abstract

Polyimide-SiO2-TiO2 nanocomposite membrane permeability, diffusivity, and selectivity were evaluated using polyimide block copolymers designed from 6F and [6F-DABA], and [SiO2-TiO2] using He, H2, CO2, O2, N2, and CH4. Nanocomposite membranes were synthesized using an in-situ sol-gel method to improve the integration of inorganic and organic phases. Metal alkoxide type and polymer functional groups were key factors affecting physical properties and gas transport. [6F-DABA]-[SiO2-TiO2] nanocomposite fractional free volume (FFV) increased 29% as compared to the unmodified [6F-DABA] polyimide. Dynamic Mechanical Thermal Analysis revealed that [SiO2-TiO2] and [TiO2] within functionalized multi-block reduced chain mobility. This led to a Tg increase from 334°C to 359°C, and tanδ to decrease from 1.9 to 0.35. In general, inorganic concentration and composition retarded polymer segmental motions, inhibited polymer chain packing, and increase predicted FFV. [6F-DABA-50]-[SiO2-TiO2] membrane's exhibited a simultaneous gas selectivity and permeability improvement. He permeability improved from 58 (unmodified polyimide) to 83 Barrers, and He/CH4 gas selectivity increased from 221 (unmodified) to 334. Membrane gas separation performance of several organic-inorganic materials exceeded Robeson's “upper bound.”