Structural evolution and nanodomain formation in blend films of a block copolymer and homopolymer

This study explores the concurrent formation of surface perforations, parallel cylinders, and double gyroids in symmetric PS- -PMMA/hPS blend films during isothermal annealing at 205 and 240 °C. By controlling the weight fraction ratio of PS- -PMMA to hPS at 75/25, we systematically examined the impact of film thickness and annealing temperature on nanodomain development. Using GISAXS and SEM, we observed that thin films rapidly formed surface perforations and underlying parallel cylinders at both annealing temperatures. For thicker films, annealing at 205 °C resulted in the coexistence of surface perforations and parallel cylinders, while annealing at 240 °C yielded the additional formation of double gyroids besides surface perforations and parallel cylinders. Furthermore, the double gyroids, which grew independently with {121} planes parallel to the substrate, did not exhibit in-plane epitaxial relationships with the other structures. These findings highlight the critical role of annealing temperature and film thickness in directing nanodomain morphology, offering new insights for the design of nanostructured materials with tailored properties.