Abstract
Aqueous Phase Separation (APS) provides a new and sustainable platform to fabricate polymeric membranes entirely in water. Still, little is known on how the casting solution and coagulation bath compositions can be used to tune membrane structure and performance. This work comprises a detailed investigation on the tuning parameters avaliable to tailor the morphology, pore size distribution, and water permeability of polyelectrolyte complex membranes prepared from poly(sodium 4-styrenesulfonate) (PSS) and polyallylamine hydrochloride (PAH). To avoid complexation of PAH and PSS in the casting solution, an optimum amount of base (NaOH) must be added to deprotonate PAH. In addition, the monomer mixing ratio of PSS to PAH significantly influences membrane morphology by modulating the interactions between the two polyelectrolytes. Coagulation bath pH can be used to control the driving force for complexation. Decreasing bath pH facilitates the formation of denser membranes, allowing ~97% protein retentions, whereas increasing bath pH leads to more open membrane structures. Changing the concentration of crosslinker in the coagulation bath allows tuning of membrane pore size from ~2 nm to ~46 nm, while simultaneously influencing membrane mechanical properties. Overall, this work highlights several key parameters to tune APS membrane morphology, demonstrating the versatility of APS to prepare optimized sustainable membranes for specific applications.
Highlights
Polymeric membranes are predominantly produced by the nonsolvent induced phase separation (NIPS) approach
polyallylamine hydrochloride (PAH) ultrafiltration type membranes was 12 wt% [19], and this was used as the starting point to further showcase the versatility of pH-triggered polyelectrolyte complexation Aqueous Phase Separation (APS)
We have systematically investigated the effect of polyelectrolyte casting solution composition and the coagulation bath conditions on the structure, morphology, and properties of poly(sodium 4-styrenesulfonate) (PSS)-PAH membranes
Summary
Polymeric membranes are predominantly produced by the nonsolvent induced phase separation (NIPS) approach. Slower precipitation rates generally result in membranes with ‘sponge-like’ morphologies This degree of control over membrane structure and pore size enabled the NIPS approach to be widely used for the fabrication of micro filtration and ultrafiltration membranes in addition to excellent supports for nanofiltration, reverse osmosis, and dense gas separation membranes [5]. Higher polymer concentrations in the casting solution result in membranes with denser structures and narrow pore size distributions [6,7,8] This is because the solvent and non-solvent exchange is slowed. The additives leach out of the casting solution into the non-solvent bath during the phase inversion process affecting the rate of polymer precipitation [11]. The findings of this work contribute towards a better understanding of how to optimize the performance of APS membranes towards specific applications
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