Pattern formation and evolution in diblock copolymer thin films above the order–disorder transition

Abstract

Research on diblock copolymer thin films has been devoted primarily toward understanding and controlling microstructural and topographical features at temperatures below the order–disorder transition (ODT), where ordered phase separated structures exist. Recently, we showed that the topography of thin liquid diblock films above the ODT form a hierarchy of patterns, depending on the film thickness. One of these topographies is a “spinodal-like” pattern. Through the use of a pair correlation analysis we show that the structural evolution of this pattern is characterized by four stages. The first involves the amplification of surface perturbations, followed by the formation of an interconnected, “spinodal-like,” pattern. The onset of the third stage is associated with the breakup of the interconnected pattern and the eventual formation of droplets of irregular shapes. The final stage involves evolution toward the formation of circular droplets.