Thermal Annealing of Solution Cast PBC Hybrid Sol-gel Nanocomposites Ionomers

Tuning the interactions of solid multiblock ionomer is a cost-effective approach to target and advance specific properties for sustainable ion-conducting applications, such as fuel cells, polymer actuators, vanadium flow batteries, water desalination using electrodialysis, and water electrolysis to produce H₂ and O₂ . In this study, polystyrene based sulfonated ionomers called pentablock copolymers (PBC) were employed due to their tailorable morphology. The morphological transitions of PBC ionomer multi blocks was induced using TEOS Sol-gel nanocomposites to understand their structure-property -transport relationship. One of the previous studies portrayed that crosslinking of TEOS-TIP sol-gel network with PBC polymer chains greatly influenced the morphology and properties of multiblock ionomer such as water uptake, proton conductivity, and liquid transport, which are crucial in the fuel cell, lithium-ion battery, or vanadium flow battery applications. However, it was found that the morphology of hybrid membranes transitioned from ordered to random morphology as more TEOS-TIP components were introduced. Hence it was postulated that thermal annealing can be a probable route to further drive the TEOS-TIP network and assemble hybrid PBC membranes into ordered structures as thermal annealing of ionomers leads to the development of interconnectivity between the adjacent ionic channels. The PBC membranes were solution cast using Tetrahydrofuran and were annealed at 80^oCand 100⁰C. The transmission SAXS analysis revealed that the thermal annealing of an unmodified PBC membrane led to the disappearance of their characteristic peaks. This may be attributed to the formation of loose clusters with higher temperature. However, the PBC incorporated with sol-gel shifted towards the lower scattering angle, indicating the formation of large sulfonic acid group clusters. This shows that thermal annealing significantly alters the microstructure of the membranes. Moreover, it was found that thermal annealing and higher TEOS content in the PBC membrane significantly reduced the water uptake by 17% but increased methanol uptake by 22.22%. Due to the enhanced crosslinking between the polymer chains with temperature, it was observed that the gas permeability of the unmodified membranes reduced significantly however the gas selectivity of hydrogen gas and carbon dioxide increased by 30%. While incorporation of sol-gel decreased both permeability and selectivity of the PBC membranes. Future study will incorporate proton conduction, mechanical durability and thermal stability of these PBC hybrid nanocomposite membranes.