Molecular Dynamics Study of Self-assembly Behavior of Block Copolymer Blend Thin Films

Thin film blends of equal lengths of cylinder- and lamella-forming diblock copolymers, denoted C and L, adopt morphologies depending on fractional composition of the blend constituents. We investigate the behavior of the thin film blends on neutral substrates that promote vertical domain orientation by means of molecular dynamics simulations. Both cylinders and lamellae coexist in separate regions in a single pattern with comparable fractions and either type of structure gradually disappears from the pattern with decreasing fraction of the corresponding type of copolymer, resulting in a spatially uniform, single type of struture. The domain spacing of cylinders increases with increasing fraction of L while that of lamellae does not nearly change with increasing fraction of C. Cylinders swell with more L despite their equal molecular weights and lamellae split into smaller ones with more C. In addition to the patterns, we study the underlying behavior of the constituent copolymer chains in each morphology and energy barriers between cylinders and lamellae.