Surface Reconstruction of the Lamellar Morphology in a Symmetric Poly(styrene-<i>block</i>-butadiene-<i>block</i>-methyl methacrylate) Triblock Copolymer:  A Tapping Mode Scanning Force Microscope Study

Abstract

The surface morphology of a symmetric poly(styrene- block -butadiene- block -methyl methacrylate) triblock copolymer (PS- b -PB- b -PMMA) with 6 wt % PB has been investigated by tapping mode scanning force microscopy (SFM). The results are compared to the bulk morphology as determined by transmission electron microscopy (TEM). In solvent-cast films PS/PMMA lamellae are formed, which are oriented nearly perpendicular to the free surface. Like in the bulk, also at the free film surface polybutadiene spheres are located at the lamellar PS/PMMA interface. However, contrary to the bulk, the surface morphology includes a large number of defects such as curved lamellar and disclinations, and the lamellar long period is doubled, from 42.7 ± 0.5 nm in the bulk to 85 ± 5 nm at the free surface, indicating a surface reconstruction. The double spacing can be explained by a surface buckling in registry with the underlying PS/PMMA lamellae. The composition of the outermost surface layer is discussed.