Self-assembly of PS-b-PNIPAM-b-PS block copolymer thin films via selective solvent annealing.

Block copolymer (BCP) thin films are interesting material systems for nanofabrication since they can form well-defined periodic nanostructures by microphase separation. However, attaining a specific morphology with the required orientation can be challenging. In this study, we investigated the morphological behavior of polystyrene- b -poly( N -isopropylacrylamide)- b -polystyrene (PS- b -PNIPAM- b -PS) BCP thin films by using Atomic Force Microscopy (AFM) and in-situ Grazing-Incidence X-ray Scattering (GISAXS) during selective solvent annealing. Thin films of a lamellar BCP were annealed by using various solvents with different selectivity for the blocks, such as PNIPAM-selective methanol, non-selective tetrahydrofuran (THF) and PS-selective toluene. Solvent annealing using methanol: THF 1:2 (v:v) or methanol: toluene 1:1 (v:v) resulted in the formation of hexagonally ordered perpendicular cylinders, whereas no sustained long-range order was found when only one type of solvent was used. PS- b -PNIPAM- b -PS BCP thin films that have hexagonally ordered perpendicular cylinders are promising for applications where thermo-responsiveness is desired, such as nanofiltration and biomedical applications. [ABSTRACT FROM AUTHOR]