Microthermal characterization of segmented polyurethane elastomers and a polystyrene-poly(methyl methacrylate) polymer blend using variable-temperature pulsed force mode atomic force microscopy

Pulsed force mode atomic force microscopy (AFM) has been used to study the morphology of three segmented polyurethane elastomers. High-contrast images are presented, showing their phase-separated structure on a scale of sever al tens of nanometers to a few hundred nanometers. The adhesion-dependent p ull-off force signal is found to be far more sensitive to local variations in mechanical properties than the stiffness-dependent indentation force sig nal. An insight into the size, shape, and distribution of phases can be obt ained from images constructed from spatial variations in surface adhesion p roperties. Comparison of images obtained both above and below the T-g of th e soft-segment material allows the spatial distribution of different phases to be characterized and the effects of surface topography to be decoupled from real changes in localized mechanical properties. Typical domain sizes are found to be at least an order of magnitude larger than those obtained b y small-angle X-ray scattering and AFM in previous studies. A novel method of constructing and interpreting AFM images of multiphase materials is used . The equipment and methodology are first demonstrated on a model polystyre ne-poly(methyl methacrylate) blend.