Fabrication of Micro-Nano Chiral Structures using Block Copolymer Self-Assembly and Buckling

Abstract

Chiral structured materials in nano and microscales present preferential absorptions of circulary polarized lights due to their mirror-reflected geometries. Based on such unique optical properties, there have been enormous efforts to fabricate these novel materials for advanced optical and biomedical applications. However, artificial constructions of the chiral nanostructures in such small scales with high enantiomeric purity are still challenging. Here I introduced novel fabrication methods for the chiral structures with structural hierarchy in micro and nano scales by using shear-induced alignments of block copolymer (BCP) thin films and mechanical instability induced buckling. Nanodomains of polystyrene-block-poly(2-vinylpyridine) BCP thin films were aligned in large area by assist of the shear-induced alignment methods, then the aligned BCP thin films were transferred to the surfaces pf stretched polydimethylsiloxane (PDMS) films by lift-off methods. After transferring the BCP thin films at specific inclined angles to the stretching directions, microwrinkles were prepared by release of strains. Resultant structures have hierarchical chiral structures in micro-nano scales. After the infiltrations of light responsive materials such as plasmonic materials into the naopatterns, the chiral micro-nanostructures presented chiroptical responses measured by circular dichroism. This approach does not necessitate lithography processes, that can be advantageous over other conventional methods for the fabrications of artificial chiral materials.