Ailoring Spatial Orientations of Microphase-Separated Cylinders and Lamellae of Block Copolymer Thin Films

In the study, I investigated microphaseseparated nanostructures of PS-P2VP thin films by annealing in binary solvent vapors of chloroform and methanol. Ordered microphase-separated nanostructures were achieved by controlling solvent annealing conditions. One of the key parameters is the compositions of binary co-solvent vapors. We also discuss the thermodynamic properties of perpendicularly-oriented nanocylinders. Firstly, I discuss different morphologies achieved in thin films upon exposure to binary solvent vapors of various fractions of chloroform and methanol. By an atomic force microscopy (AFM) and grazing-incident small-angle X-ray scattering (GISAXS), I identified that the nanostructures were comprised of perpendicularly-oriented cylinders with hexagonal lattice, the coexistence of parallel-oriented cylinders and perforated lamellae , and parallel-oriented lamellae with gradually increasing the proportion of methanol in the cosolvent vapors. In particular, when PS-P2VP thin films were annealed in chloroform for a long time period vertically-oriented cylinders were obtained. By contrast, parallel-oriented lamellae were obtained when post-annealing was carried out twice in chloroform vapor, we would obtain a spherical morphology. Besides, we use theoretical calculation to explain the influence of added methanol vapor on the thin film stability.