The storage modulus (E') and loss modulus (E") of polyolefin blends have been mapped on the nanoscale with contact resonance force microscopy (CR-FM), a dynamic contact mode of atomic force microscopy (AFM). CR-FM maps for a blend of polyethylene, polypropylene, and polystyrene were compared to results at the corresponding frequency calculated from bulk dynamic mechanical analysis (DMA) values. Absolute values for E' obtained by CR-FM were in good agreement with those from DMA, but the CR-FM results for E" were consistently lower than DMA values. However, semiquantitative?trends in E from the CR-FM maps compared favorably with DMA results. Application of CR-FM to an elastomer-containing blend resulted in moduli maps that were inconsistent with bulk values. The discrepancy was attributed to the large tip-sample adhesion force of the elastomer, which is not measured or considered in the current CR-FM implementation. In spite of this limitation, our results demonstrate the potential of contact resonance methods for quantifying nanoscale viscoelastic properties of stiff polymers.
Pub Type: Journals