Morphology Transition of Block Copolymer Surface Micelles by Solvent Immersion*

   While amphiphilic block copolymers (BCPs) form micelles in a selective solvent, they form surface micelles at the air-water interface in a similar manner but different chain conformation. Unlike BCP micelles in solution, the structure of surface micelles can be effectively varied by changing surface pressure.

   In this study, we report that BCP surface micelles which were transferred from the air-water interface to a substrate can transform into diverse nanostructures with direct immersion in specific solvents. Initial hexagonal array of surface micelles transformed into unique nanostructures such as toroids, split dots, and inverse micelles, which is attributed to complex interactions between polymer chains, substrate, and solvents. We investigate the phenomena by varying the molecular weight of BCPs, surface pressure, solvent immersion time, and further discuss how these parameters alter the rearrangement kinetics of the surface micelles. Based on the understanding of complex chain dynamics upon solvent immersion, our research provides a new strategy to fabricate a uniform array of diverse BCP nanopatterns.