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

Proceedings of the National Academy of Sciences of the United States of America
Manesh GopinadhanChinedum O Osuji

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, inclu...Continue Reading

References

Aug 1, 1986·Physical Review. B, Condensed Matter·J D Axe, Y Yamada
Nov 26, 2010·Journal of the American Chemical Society·Pawel W MajewskiChinedum O Osuji
May 22, 2013·ACS Nano·Helen TranLuis M Campos
Jun 5, 2014·Advanced Materials·Manesh GopinadhanChinedum O Osuji
Jan 2, 2016·Physical Review Letters·Yekaterina RokhlenkoKevin G Yager

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