Surface Properties of Elastomeric Polypropylenes Studied with Atomic Force Microscopy

The energy dissipated between tip and sample during dynamic atomic force microscopy (AFM) is a sensitive measure of local surface properties. We mapped the surface properties of crystalline and amorphous regions in thin films of different kinds of elastomeric polypropylene (ePP) with 10 nm lateral resolution. The dissipated energy as a function of the amplitude setpoint displays discriminative shapes for both polymer regions. Differences in the shape as well as in the maximum amount of dissipated energy are interpreted as different amounts of amorphous material on top of crystalline regions. Indentation experiments at different amplitude setpoints resulted in indentation depths of the AFM tip up to 11 nm, on both crystalline and amorphous regions. This and the change of dissipated energy upon wet chemical etching indicate that crystalline regions are covered by an up to 10 nm thick amorphous layer.