Magnetic alignment of block copolymer microdomains by intrinsic chain anisotropy

TL;DR

This study demonstrates that intrinsic chain anisotropy in block copolymers can drive magnetic field-induced alignment of microdomains, enabling controlled orientation of mesophases with potential applications in materials design.

Contribution

The paper reveals that intrinsic chain susceptibility anisotropy alone can induce strong magnetic alignment in block copolymer microdomains, supported by experimental and computational analysis.

Findings

Alignment occurs during cooling across the disorder-order transition.

Susceptibility anisotropy magnitude is approximately 2×10^{-8}.

Aligned grains are about 1.2 μm in size during the process.

Abstract

We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using \textit{in situ} X-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, $\Delta\chi$, that drives alignment, and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding $\Delta\chi\approx 2\times10^{-8}$. From field-dependent scattering data we estimate grains of $\approx1.2$ $\mu$m are present during alignment. These results demonstrate that intrinsic anisotropy is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.