4.8 Article

Surface Segregation and Self-Assembly of Block-Copolymer Separation Layers on Top of Homopolymer Substructures in Asymmetric Ultrafiltration Membranes from a Single Casting Step

期刊

ADVANCED FUNCTIONAL MATERIALS
卷 31, 期 29, 页码 -

出版社

WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.202009387

关键词

block copolymer self‐ assembly; polymer blend; surface segregation; ultrafiltration membranes

资金

  1. National Science Foundation [DMR-1707836]
  2. NSF MRSEC program [DMR-1719875]
  3. JSPS KAKENHI [JP1039865]

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Surface segregation in blended polymer films has attracted significant interest, and a strategy to control this phenomenon in thin block-copolymer layers has been described in this study. By utilizing nonsolvent induced phase separation, solidified bilayer ultrafiltration membranes with self-assembled BCP top layers atop homopolymer substructures can be fabricated in a single casting step. Key factors for successful BCP surface segregation include careful selection of solvent systems and stabilization of micellar structures.
Surface segregation in blended polymer films has attracted much interest in fundamental research as well as for practical applications. A variety of methodologies have been proposed for controlling surface segregation. They often require long annealing times, however, to achieve thermodynamic equilibrium. Here, a strategy and proof-of-principle experiments are described to control surface segregation of thin block-copolymer (BCP) layers on top of a homopolymer in a single casting step from blended BCP/homopolymer solutions. The surface coverage by the minor constituent BCP (2-10 wt%) is accomplished despite almost identical surface energies of BCP and homopolymer constituents. Immersing this casted solution into water for nonsolvent induced phase separation (NIPS), a nonequilibrium process, affords solidified bilayer ultrafiltration membranes composed of a thin porous surface layer of self-assembled BCP atop an asymmetric porous homopolymer substructure. Key to successful BCP surface segregation is the choice of a binary solvent system based on careful considerations of solvent surface energies and polymer-solvent interaction parameters. Furthermore, stabilizing the BCP micellar structure by a divalent metal additive is also essential. The approach provides a cost-effective method for fabricating bilayer-type asymmetric ultrafiltration membranes with uniform BCP self-assembly based selective top surface pore layers in a single casting step.

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