Latent Alignment in Pathway-Dependent Ordering of Block Copolymer Thin Films
Majewski, P.W.; Yager, K.G. "Latent Alignment in Pathway-Dependent Ordering of Block Copolymer Thin Films" Nano Letters 2015
We use photo-thermal shearing to study the pathway-dependence of ordering in self-assembly. We find that very brief (sub-second) photo-shearing can induce a nearly-imperceptible alignment in a soft-matter film. This subtle alignment biases ordering, such as subsequent isotropic annealing (no orientational bias) rapidly yields a highly-aligned state.
Block copolymers spontaneously form well-defined nanoscale morphologies during thermal annealing. Yet, the structures one obtains can be influenced by nonequilibrium effects, including processing history or pathway-dependent assembly. Here, we explore various pathways for ordering of block copolymer thin films, using oven-annealing, as well as newly disclosed methods for rapid photothermal annealing and photothermal shearing. We report the discovery of an efficient pathway for ordering self-assembled films: ultrarapid shearing of as-cast films induces “latent alignment” in the disordered morphology. Subsequent thermal processing can then develop this directly into a uniaxially aligned morphology with low defect density. This deeper understanding of pathway-dependence may have broad implications in self-assembly.