The ordering of thin films of symmetric diblock copolymers

Abstract

The ordering of thin films of symmetric diblock copolymers of polystyrene and polymethylmethacrylate has been investigated by neutron reflectivity. It is shown that the order-disorder transition temperature depends strongly on the film thickness, increasing as the film thickness decreases. The transition is shown to lose all its first-order characteristics in the thin films. For films thinner than ∼2000 A it is not possible to obtain the copolymer flms in the disordered state at temperatures below the decomposition temperature. A transition is observed where the copolymer goes from a partially to a fully ordered state. For thick specimens, this transition corresponds to the bulk order-disorder transition temperature. However, for thinner specimens this transition temperature depends on the film thickness in a power law manner.