Heterogeneous viscoelasticity under uniaxial elongation of isoprene rubber vulcanizate investigated by nanorheological atomic force microscope and dynamic mechanical analysis

Abstract

In this study, vulcanized isoprene rubber (IR) under uniaxial stretch was examined by two different methods. One was conventional dynamic mechanical analysis (DMA), while this attempt to perform DMA testing on largely deformed specimen was quite challenging and gave a new insight on the rheological behavior of stretched rubber molecules. Another was nanorheological atomic force microscope (AFM), which was developed by the authors. The method provided spatially-resolved images of storage modulus, loss modulus and loss tangent at wide frequency ranges. The IR vulcanizate exhibited heterogeneous structure visualized by AFM, in which stretched and non-stretched regions were visible, showing non-affine nature of the specimen. Viscoelastic properties were examined in terms of elongation ratios, frequencies with comparing macroscopic and microscopic responses, where both measurements gave almost similar results to each other. The storage modulus at rubbery plateau region was increased upon large deformation in both measurements. The main finding was that the viscous response was not enhanced until the specimen experienced large deformation.