2025 AIChE Annual Meeting

(565e) How Does a Rubbery Block Impact the Mechanical and Transport Properties of Tetrablock Polymer Membranes?

Authors

Adam Mann - Presenter, The University of Texas at Austin
Noah Wamble, University of Notre Dame
Louise Kuehster, University of Oklahoma
Anthony Arrowood, The University of Texas at Austin
Nathaniel Lynd, University of Texas at Austin
Benny D. Freeman, University of Texas at Austin
Gabriel Sanoja, Univeristy of California-Berkeley
Nonsolvent-induced phase separation (NIPS) is widely used to fabricate ultrafiltration membranes, but its nonequilibrium nature often results in disordered surfaces that limit transport performance. Using amphiphilic block polymer self-assembly can induce surface ordering; however, most of the block copolymers are based on poly(styrene), which is very brittle. Designing membranes with optimal transport and mechanical properties is critical for scale-up to industrial use.

One way to improve the mechanical properties of brittle glassy polymers is through the inclusion of an energy-dissipating rubbery component. This study explores the effect of poly(isoprene) (PI) content on the mechanical/fracture properties of the bulk polymer and the transport performance of the resulting phase-inversion membranes in an amphiphilic tetrablock poly(styrene)-b-poly(isoprene)-b-poly(styrene)-b-poly(4-vinyl pyridine) (SISV) system. Four block polymers with varying PI midblock content (0 to 36 wt%) were synthesized, keeping the P4VP content and overall molecular weights constant. Using the copper grid technique developed by Lauterwasser and Kramer1 and tensile tests, a two-step change in fracture behavior was observed - from brittle to rubber-toughened thermoplastic to thermoplastic elastomer - as PI content increased. This change in fracture mechanism was attributed to changes in the self-assembled morphology, observed with AFM imaging, which were brought about by the PI content. Membranes manufactured by SNIPS exhibited a transition from ordered to more disordered surface morphology with increasing PI, which affected the MWCO and PEG rejection profile, while maintaining high pure water permeance (~1,000 LMH/bar). Overall, these results highlight the delicate balance inherent to co-designing mechanical and transport performance in state-of-the-art membranes.

1. Lauterwasser, B.D. & Kramer, E.J. Philosophical Magazine A 39, 469-495 (1979)