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Issue 5, 2017
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Directing block copolymer self-assembly with permanent magnets: photopatterning microdomain alignment and generating oriented nanopores

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Abstract

Magnetic fields are useful for directing block copolymer (BCP) self-assembly, but to date such a field alignment has required large fields (>5 T) necessitating the use of superconducting magnets. We report an approach that circumvents this limitation by introducing labile reactive mesogens into a liquid crystalline (LC) BCP based on a norbornene backbone with a poly(lactide) minority block that forms hexagonally packed cylinders. The free mesogens co-assemble with the smectic A mesophase of the BCP and enable alignment at fields as low as 0.5 T. The remarkable field response originates from the combined effects of enhanced mobility and decreased segregation strength, and the presence of large micron-scale grains in the system. We demonstrate a robust alignment of mesogen-blended samples using simple permanent magnets. The etching of poly(lactide) yields nanoporous films, while the spatially selective microdomain immobilization by UV-induced crosslinking through a photomask provides a versatile mechanism for creating alignment patterns. We anticipate that the nanoporous materials as generated here may find application in membrane fabrication or BCP lithography, while the ability to spatially pattern alignment is promising for the design of mechanical metamaterials exploiting the shape memory effect of LC elastomers.

Graphical abstract: Directing block copolymer self-assembly with permanent magnets: photopatterning microdomain alignment and generating oriented nanopores

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Supplementary files

Article information


Submitted
04 Aug 2017
Accepted
27 Sep 2017
First published
23 Oct 2017

Mol. Syst. Des. Eng., 2017,2, 549-559
Article type
Paper

Directing block copolymer self-assembly with permanent magnets: photopatterning microdomain alignment and generating oriented nanopores

M. Gopinadhan, Y. Choo, L. H. Mahajan, D. Ndaya, G. Kaufman, Y. Rokhlenko, R. M. Kasi and C. O. Osuji, Mol. Syst. Des. Eng., 2017, 2, 549
DOI: 10.1039/C7ME00070G

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