Unconventional Morphologies of Symmetric, Diblock Copolymers Due to Film Thickness Constraints

Abstract

The morphology of thin films of symmetric, diblock copolymers of polystyrene (PS) and poly-(methyl methacrylate) (PMMA) has been investigated as a function of film thickness where the total thickness of the films was less than or equal to 3L/2 where L is the period of the lamellar microdomain in the bulk. In all cases, a layered, lamellar morphology oriented parallel to the surface of the film was found. However, the thicknesses of the PS and PMMA layers and the width of the interface between the layers were found to vary with film thickness. Finally, in the case of a film with a thickness of L, a phase-mixed morphology on top of underlying layers of PS and PMMA was found, demonstrating a marked perturbation on the morphology of the diblock copolymer in this upper layer from that seen usually in thin multilayer films and in the bulk. The results from these studies were found to be in agreement with X-ray reflectivity and X-ray photoelectron spectroscopy studies. © 1991, American Chemical Society. All rights reserved.