Sprecher
Beschreibung
This contribution addresses the morphological properties of silica nanofillers embedded in styrene-butadiene elastomers and their structural rearrangement upon an applied deformation. Time-resolved ultra-small x-ray scattering (USAXS) patterns have been collected under the effect of a periodic deformation with variable dynamic amplitudes applied in-situ by means of a home-built DMA (Dynamic Mechanical Analysis) rheometer. The correlation between the structural evolution of the filler clusters under large-amplitude oscillatory extension (LAOE), detected by x-ray scattering, and the dynamic-mechanical stress-strain response is accessed by the in-situ configuration. This specific combination of scattering and rheological methods allows a simultaneous identification of the induced structural changes on a microscopic level and the macroscopic mechanical properties. A mathematical scattering model that provides a quantitative description of the filler network evolution under the effect of a dynamic deformation is here introduced. With the aim of addressing the Payne effect and the underlying structural modifications correlated to intra- and inter-filler-aggregate effects, all rubbers were pre-conditioned to suppress stress softening related to the Mullins effect. 2D scattering images as well as the corresponding averaged intensities reveal a re-arrangement of the filler clusters along the direction of the applied dynamic sinusoidal deformation. From the structural study of the filler, a jamming/de-jamming transition between the filler clusters is identified as one contributor to non-linear viscoelastic behavior of the rubber and associated with structural arrest of the dynamics by the percolation of rigid fillers. The dynamic stress response of the full composite shows an onset of non-linear behavior, and odd and even higher harmonics of the fundamental excitation frequency are evidenced.