Pathway-engineering for highly-aligned block copolymer arrays
Choo, Y.; Majewski, P.W.; Fukuto, M.; Osuji, C.O.; Yager, K.G. "Pathway-engineering for highly-aligned block copolymer arrays" Nanoscale 2018
While kinetic aspects of self-assembly can hinder ordering, non-equilibirum effects can also be exploited to enforce a particular kind of order. We develop a pathway-engineering approach, using it to select a particular arrangement of a block copolymer cylinder phase.
While the ultimate driving force in self-assembly is energy minimization and the corresponding evolution towards equilibrium, kinetic effects can also play a very strong role. These kinetic effects, such as trapping in metastable states, slow coarsening kinetics, and pathway-dependent assembly, are often viewed as complications to be overcome. Here, we instead exploit these effects to engineer a desired final nano-structure in a block copolymer thin film, by selecting a particular ordering pathway through the self-assembly energy landscape. In particular, we combine photothermal shearing with high-temperature annealing to yield hexagonal arrays of block copolymer cylinders that are aligned in a single prescribed direction over macroscopic sample dimensions. Photothermal shearing is first used to generate a highly-aligned horizontal cylinder state, with subsequent thermal processing used to reorient the morphology to the vertical cylinder state in a templated manner. Finally, we demonstrate the successful transfer of engineered morphologies into inorganic replicas.