Nanorheological Mapping of Rubbers by Atomic Force Microscopy

A novel atomic force microscopy (AFM) method is used for nanometer-scale mapping of the frequency dependence of the storage modulus, loss modulus, and loss tangent (tan delta) in rubber specimens. Our method includes a modified AFM instrument, which has an additional piezoelectric actuator placed between the specimen and AFM scanner. The specimen and AFM cantilever are oscillated by this actuator with a frequency between 1 Hz and 20 kHz. On the basis of contact mechanics between the probe and the sample, the viscoelastic properties were determined from the amplitude and phase shift of the cantilever oscillation. The values of the storage and loss moduli using our method are similar to those using bulk dynamic mechanical analysis (DMA) measurements. Moreover, the peak frequency of tan delta corresponds to that of bulk DMA measurements.