Controlling orientational order in block copolymers using low-intensity magnetic fields

Manesh Gopinadhan, Youngwoo Choo, Kohsuke Kawabata, Gilad Kaufman, Xunda Feng, Xiaojun Di, Yekaterina Rokhlenko, Lalit H. Mahajan, Dennis Ndaya, Rajeswari M. Kasi, Chinedum O. Osuji

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP’s anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields (<0.5 T) that are accessible using permanent magnets, in contrast to the high fields (>4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system’s nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles.

Original languageEnglish
Pages (from-to)E9437-E9444
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue number45
DOIs
Publication statusPublished - 2017 Nov 7
Externally publishedYes

Keywords

  • Aligned polymers
  • Block copolymers
  • Liquid crystals
  • Magnetic field processing
  • Self-assembly

ASJC Scopus subject areas

  • General

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