Highly selective and water permeable dual-layer ultrafiltration (UF) membranes comprising a disordered poly(methyl methacrylate-stat-styrene)-block-poly(lactide) selective layer and a polysulfone (PSF) support layer were fabricated using a co-casting technique. A dilute solution of diblock polymer was spin coated onto a solvent-swollen PSF layer, rapidly heated to dry and disorder the block polymer layer, and subsequently immersed into an ice water coagulation bath to kinetically trap the disordered state in the block polymer selective layer and precipitate the support layer by nonsolvent-induced phase separation. Subsequent removal of the polylactide block generated porous membranes suitable for UF. The permeability of these dual-layer membranes was modulated by tuning the concentration of the PSF casting solution, while the size-selectivity was maintained because of the narrow pore size distribution of the self-assembled block polymer selective layer. Elimination of the thermal annealing step resulted in a dramatic increase in the water permeability without adversely impacting the size-selectivity, as the disordered nanostructure present in the concentrated casting solution was kinetically trapped upon rapid drying. The co-casting strategy outlined in this work may enable the scalable fabrication of block polymer membranes with both high permeability and high selectivity.
Bibliographical noteFunding Information:
The authors would like to thank Dr. Daphne Chan for helpful advice and Prof. Lorraine Francis for carefully reviewing the manuscript. ALTASORB generously donated lactide. Funding for this work was provided by the National Science Foundation (DMR-1609459 and DMR-2003454). The Hitachi SU8320 microscope was provided by NSF MRI DMR1229263. Parts of this work were carried out in the Characterization Facility, UMN, which receives partial support from NSF through the MRSEC program. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by the Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. This research used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Data were collected using an instrument funded by the NSF under award number 0960140.
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- block polymer
- composite membrane
- order-disorder transition