Evolution of Ordering in Thin Films of Symmetric Diblock Copolymers

The manner in which thin films of asymmetric diblock copolymer of polystyrene and poly(methyl methacrylate) form a multilayered structure has been investigated by transmission electron microscopy and neutron reflectivity. It is shown that spin coated films of the diblock copolymer are initially microphase separated with an average repeat period that is much smaller than the equilibrium period. Upon heating, two different relaxations were found. One involves a rapid, local relaxation of the copolymer chains in which the phase size increases to a size scale comparable to the equilibrium period. However, the microstructure is a bicontinuous network of polystyrene and poly(methyl methacrylate). Upon further heating the copolymer chains are transported within the bicontinuous network to form the multilayered structure.