Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy
Rokhlenko, Y.; Gopinadhan, M.; Osuji, C.O.; Zhang, K.; O’Hern, C.S.; Larson, S.R.; Gopalan, P.; Majewski, P.W.; Yager, K.G. "Magnetic Alignment of Block Copolymer Microdomains by Intrinsic Chain Anisotropy" Physical Review Letters 2015
The ordering of low molecular weight block copolymers in a magnetic field is studied. Variance scattering methods are used to quantify the exceptionally large grain sizes. The magnetic orientation is demonstrated to arise from the intrinsic magnetic response of the polymer chains.
We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using 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 ~ 2×10^-8. From field-dependent scattering data, we estimate that grains of ~1.2 um 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.