Triggering Mesophase Order in Melts of Metastable, Ultrathin Diblock Copolymer Films through Microstretching: Effect of Melt Film Thickness

摘要

By means of a sharp atomic force microscopy (AFM) probe, we have induced the formation of lamellar structures with nanoscale size in ultrathin films of melted poly(1,4-butadiene)-block-poly(ethylene oxide) (BD84-EO110,f(PB) = 0.55) at temperatures above the melting temperature of the PEO block and below the order-disorder transition temperature of the copolymer (T-m < T < T-ODT). The morphology of films 30-50 nm thick is mainly featureless except for the presence of a few monolamellar nanopatches. The absence of an overall lamellar structure, the typical mesophase encountered in this kind of copolymers, Suggests that the ultrathin Films are arrested in the disordered state. However, repetitive loading-unloading cycles exerted with the AFM probe in the structureless regions lead to the formation of multilamellar islands consisting of 2-9 layers 10-12 nm thick at precise locations. The size, shape, and number of layers of these islands can be controlled by tuning the size of probed area, the loading-unloading rate, and the overall film thickness.