Dynamic Moduli Mapping of Silica-Filled Styrene-Butadiene Rubber Vulcanizate by Nanorheological Atomic Force Microscopy

Atomic force microscopy (AFM) offers nano scale mapping of materials' properties. Especially, our modified AFM termed nanorheological AFM enables us to measure the accurate frequency-dependent storage and loss moduli and loss tangent over a sixth-order frequency range without any temperature control at nanoscale resolution. These dynamic properties obtained by nanorheological AFM can be compared with those using bulk dynamic mechanical analysis (DMA) measurements. In this paper, we applied this technique to silica filled styrene-butadiene rubber (SBR) to investigate the nature of the interfacial rubber region existing between a rubber matrix and silica particles at different temperatures. The dynamics properties of the interfacial rubber region were different from those of matrix rubber regions. The master curve obtained by this technique perfectly coincided with that by bulk DMA. Furthermore, it was found that the behavior of bulk loss tangent could be predicted by the contributions from both matrix and interfacial rubber regions, which assures the importance of interface control often adopted in the tire industry to change tire performances. By examining the frequency-dependent change of loss modulus from the glass rubber transition state to the glassy state, we also found for the first time that this transition does not occur uniformly but inhomogeneously depending on spatially heterogeneous polymer segmental dynamics.