Tapping-Mode AFM Studies Using Phase Detection for Resolution of Nanophases in Segmented Polyurethanes and Other Block Copolymers

Abstract

The nanophase separated hard segment domains in solvent cast films of a segmented polyurethane and a segmented polyamide elastomer were imaged in real space using phase and topographical information from tapping-mode AFM techniques. A styrene triblock copolymer was used as a control to demonstrate the contrast mechanisms. For the segmented polyurethane and polyamide elastomers, contrast results from local stiffness variations of hard domains beneath a ca. 1 nm thick soft segment overlayer. Domain sizes and dispersity, shape, orientation, spacing, and uniformity in space are uniquely extracted from these real space AFM data. The ca. 7 nm diameter domains were relatively symmetric and uniformly space filling in the polyurethane. They were lamellar or sheetlike in the segmented polyamide elastomer, with a high aspect ratio and no curvature. There was no obvious correlation of lamellae orientation with macrocrystal aggregate (spherulite) position in the polyamide copolymer, while no such aggregates exist in the polyurethane.