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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 Å 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. [ABSTRACT FROM AUTHOR]

The morphology of thin films of symmetric diblock copolymers has been investigated by neutron and X-ray reflectivity and X-ray photoelectron spectroscopy, for thicknesses less than 3L/2, where L is the long period of the lamellar morphology in the bulk. The constrains placed on a copolymer film by the presence of the two surfaces can produce severe perturbations on the morphology, due to the interactions of the copolymer blocks with the air and the substrate interfaces. It is possible to induce variations in the chain extension and in the interfacial mixing, and to force a normally microphase separated copolymer into a homogenecous state. [ABSTRACT FROM AUTHOR]