In this paper, we introduce AFM-nDMA, a new AFM-based method for characterizing viscoelastic properties of materials. Bulk viscoelastic measurements are routine in establishing the structure-property relationship for heterogeneous materials, such as polymer composites, blends, and multilayers. However, materials R&D often produces composites that contain nano-sized portions that do not exist in the bulk or that have properties influenced by the proximity of other components. AFM has the resolution and force sensitivity needed to investigate the local properties of these materials, but traditional AFM-based approaches are hampered by difficult calibration, poorly defined measurement frequency, and inadequate modeling of the tip-sample interaction.
Excellent agreement was obtained between our AFM-nDMA measurements and those collected with bulk DMA when measuring viscoelastic properties of bulk samples. Since AFM-nDMA provides spectra of storage and loss modulus at well-defined frequencies and temperatures, it was possible to generate viscoelastic master curves through Time-Temperature Superposition from the AFM data. Storage modulus and loss tangent mapping and co-located spectra were also investigated for two polymer blends to demonstrate the measurement of property variations within microscopic domains that are inaccessible to bulk measurements.