Vertical Lamellae Formed by Two-Step Annealing of a Rod–Coil Liquid Crystalline Block Copolymer Thin Film
Shi, L.-Y.; Lan, J.; Lee, S.; Cheng, L.-C.; Yager, K.G.; Ross, C.A. "Vertical Lamellae Formed by Two-Step Annealing of a Rod–Coil Liquid Crystalline Block Copolymer Thin Film" ACS Nano 2020
We explore orientation control in silicon-containing block copolymer thin films via multi-step annealing.
Silicon-containing block copolymer thin films with high interaction parameter and etch contrast are ideal candidates to generate robust nanotemplates for advanced nanofabrication, but they typically form in-plane oriented microdomains as a result of the dissimilar surface energies of the blocks. Here, we describe a two-step annealing method to produce vertically aligned lamellar structures in thin film of a silicon-containing rod–coil thermotropic liquid crystalline block copolymer. The rod–coil block copolymer with the volume fraction of the Si-containing block of 0.22 presents an asymmetrical lamellar structure in which the rod block forms a hexatic columnar nematic liquid crystalline phase. A solvent vapor annealing step first produces well-ordered in-plane cylinders of the Si-containing block, then a subsequent thermal annealing promotes the phase transition from in-plane cylinders to vertical lamellae. The pathways of the order–order transition were examined by microscopy and in situ using grazing incidence small-angle X-ray scattering and wide-angle X-ray scattering.