Rapid Ordering in “Wet Brush” Block Copolymer/Homopolymer Ternary Blends
Doerk, G.S.; Yager, K.G. "Rapid Ordering in “Wet Brush” Block Copolymer/Homopolymer Ternary Blends" ACS Nano 2017
We explore how blending low-molecular-weight homopolymer into block copolymer phases allows them to order much more rapidly. A surprisingly large amount of homopolymer can be blended, allowing for vastly accelerated coarsening kinetics.
The ubiquitous presence of thermodynamically unfavored but kinetically trapped topological defects in nanopatterns formed via self-assembly of block copolymer thin films may prevent their use for many envisioned applications. Here, we demonstrate that lamellae patterns formed by symmetric polystyrene-block-poly(methyl methacrylate) diblock copolymers self-assemble and order extremely rapidly when the diblock copolymers are blended with low molecular weight homopolymers of the constituent blocks. Being in the “wet brush” regime, the homopolymers uniformly distribute within their respective self-assembled microdomains, preventing increases in domain widths. An order-of-magnitude increase in topological grain size in blends over the neat (unblended) diblock copolymer is achieved within minutes of thermal annealing as a result of the significantly higher power law exponent for ordering kinetics in the blends. Moreover, the blends are demonstrated to be capable of rapid and robust domain alignment within micrometer-scale trenches, in contrast to the corresponding neat diblock copolymer. These results can be attributed to the lowering of energy barriers associated with domain boundaries by bringing the system closer to an order–disorder transition through low molecular weight homopolymer blending.