Effects of metal loading and magnetic field strength on alignment of noncrystalline block copolymers doped with metal complexes

Hiroaki Wakayama,Hirotaka Yonekura,Masashi Harada

doi:10.1007/s10965-014-0488-2

Hiroaki Wakayama, Hirotaka Yonekura + Show 1 more

Open Access

https://doi.org/10.1007/s10965-014-0488-2

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Abstract

Control of the orientation of block copolymers in self-assembled nanostructures is important for their applications in organic semiconductors, lithographic nanopatterning, separation membranes, and nanofabrication templates. We recently reported that addition of magnetically sensitive metal complexes to block copolymers can be used to align the block copolymers under the influence of a magnetic field. In the present study, we investigated the mechanism of magnetic alignment of block copolymers doped with metal complexes. Specifically, we used small-angle X-ray scattering analysis to evaluate the effects the metal complex molar ratio and the strength of the applied magnetic field have on magnetic alignment in block copolymer–metal composites. Two Fe precursors, tricarbonyl(cyclooctatetraene) iron and acetylacetonate iron(III), and one Pt precursor, platinum dimethylcyclooctadiene, were selectively introduced into separate polymer blocks of a block copolymer, polystyrene-block-poly(2-vinylpyridine) (PS-P2VP, 102 k/97 k) or polystyrene-block-poly(4-vinylpyridine) (PS-P4VP, 40 k/5.6 k), and the resulting films were annealed in a magnetic field. We found that magnetic alignment of the block copolymers was enhanced by high metal complex molar ratios and high magnetic field strength. The lamellar structures of the self-assembled PS-P2VP(102 k/97 k) composites were disturbed when the amounts of the metal complexes were increased, and magnetic alignment of the lamellar structures was enhanced when the strength of the applied magnetic field was increased. Magnetic alignment induced shrinkage of the cylindrical structures of the self-assembled PS-P4VP(40 k/5.6 k) composites with high metal complex ratios.

Highlights

Block copolymers are attracting much attention because of their ability to self-assemble into periodically ordered nanostructures
Scanning transmission electron microscopy images of samples that were prepared with PS-P2VP(102 k/97 k) and PSP4VP(40 k/5.6 k) and metal complexes at molar ratios of 1.0 and that were annealed in a 10 T magnetic field showed lamellar and cylindrical structures, respectively, that were almost exactly parallel to the direction of the applied magnetic field (Fig. 1)
In the small-angle X-ray scattering (SAXS) pattern of a sample prepared with PS-P4VP(102 k/97 k) without metal complexes and at magnetic field strength of 10 T, the relative positions of the 1:2:3 peaks confirmed that the sample had a lamellar structure (Fig. 3a metal complex molar ratio, 0.0; blue line)

Summary

Introduction

Block copolymers are attracting much attention because of their ability to self-assemble into periodically ordered nanostructures. Scanning transmission electron microscopy images of samples that were prepared with PS-P2VP(102 k/97 k) and PSP4VP(40 k/5.6 k) and metal complexes at molar ratios of 1.0 and that were annealed in a 10 T magnetic field showed lamellar and cylindrical structures, respectively, that were almost exactly parallel to the direction of the applied magnetic field (Fig. 1).

Results

Conclusion