Characteristics of the Surface-Induced Orientation for Symmetric Diblock PS/PMMA Copolymers

The characteristics of the surface-induced orientation of symmetric diblock poly(styrene-6-methyl methacrylate) copolymers PS/PMMA, as revealed by dynamic secondary ion mass spectroscopy (SIMS) are presented. The lamellar morphology is found to orient parallel to the surface of the substrate with a lateral coherence on the order of 80 μm. On silicon substrates, the total film thickness is given by (n +1/2)L where L is the lamellar period and n is the number of periods, whereas on a gold substrate the thickness is given by nL. The ordering results from a preferential location of PS on the gold substrate and at the air/copolymer interface and of PMMA on the silicon substrate. Time-dependent annealing studies on thick specimens above the glass transition show that the orientation is induced at both the air/copolymer and the copolymer/substrate interfaces and propagates through the entire specimen. For samples prepared on silicon substrates where the total film thickness is less than L, a microphase-separated morphology is not found. Here only gradients in the composition of each component at the interfaces are found. Finally, the preparation of films under slow-evaporation conditions from solvents that preferentially solvate one of the components induces an oriented, nonequilibrium morphology. © 1989, American Chemical Society. All rights reserved.