Nondestructive depth-resolved imaging of ~20-nm-thick surface layers of soft polymeric materials is achieved with amplitude modulation atomic force microscopy (AFM). From measurements of the amplitude and the phase as function of tip-sample distance, the tip indentation into the compliant specimen is determined. It serves as a depth coordinate for reconstructing cross sections and volume images of the specimen's mechanical properties. Using this method we revealed subsurface structures that are not discernible with conventional AFM, such as the local thickness of amorphous surface layers on semicrystalline polythiophenes and the detailed shape of crystalline lamella in elastomeric polypropylene. The nanoscale deformation processes that occur upon stretching thin films of elastomeric polypropylene are studied using a microtensile testing setup integrated in the AFM. Here we discovered quadrangular complexes of crystalline lamellae that display locally auxetic behavior (negative Poisson's ratio) on the 100-nanometer scale. This indicates that auxetic behavior is an intrinsic property of certain semicrystalline polymers.

Imaging subsurface structure and nanoscale deformation processes in polymeric materials

244th National Meeting (2012)

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