Rapid and Tunable Structuring of Block Copolymer Films using Controlled Solvent Swelling*

We have studied the effect of the film swelling ratio on the phase separation of polystyrene-b-poly(vinylpyridine) (PS-b-PVP) block copolymer (BCP) nanopatterns by precisely controlling solvent uptake into the film. Using a custom-built annealing chamber with an inbuilt reflectometer, swelling ratios of up to 10x were achieved in a controlled vapor environment using a variety of solvents. The swelling behaviour of two different PVP molecular systems were studied, one of low molecular weight (~35 kg/mol) and another of high molecular weight (~800 kg/mol). Our results suggest that above a maximum swelling threshold, the ordering of BCP nanopatterns becomes extremely sensitive to slight variations in temperature and vapor pressure. By precisely controlling such variations, we successfully synthesized a surprisingly varied range of BCP morphologies from these individual systems, including highly sensitive metastable phases. Additionally, in comparison to conventional solvent vapor annealing methods we found that such highly ordered structures could be achieved in a matter of minutes rather than hours. A diffusion model is proposed to explain the kinetic effect, and the route to a rapid self-assembly process in BCP films.