165HIGHLIGHTS 2020

IN-SITU DYNAMIC MECHANICAL ANALYSIS AND SAXS STUDIES OF SILICA-RUBBER COMPOSITES Nano-composite materials can be tailored to suit many applications through their hierarchical structures spanning many length scales. In-situ experiments at beamline ID02 provide an understanding of the microscopic deformation characteristics of silica-rubber composites.

Nanofillers within elastomers form hierarchical structures varying from the nanometre to the micrometre scale. Consequently, nano- composite materials, such as those used in car tyres, exhibit strongly improved dynamic mechanical properties. In-situ small-angle X-ray scattering can reveal the correlation between the filler structure and the associated macroscopic dynamic properties.

The scattering function of silica-filled styrene- butadiene random copolymer rubbers (SBR) under a continuous uniaxial strain cycle was investigated using ultrasmall-angle X-ray scattering (USAXS) at beamline ID02. The microscopic hierarchical arrangement of aggregating nanofiller particles in the rubber matrix was determined at different strain stages up to a 100% increase in the initial sample length. Scattering patterns reveal the size and distribution of clusters formed by primary particles and relate to the stress in the elastomers.

Figure 143 illustrates different evolutions of the cluster parameters. In case A, due to the initial orientation of the clusters in a direction perpendicular to the deformation axis, the strain field in the matrix promotes a re-orientation of primary particles inside the clusters, which is reversible upon unloading. In case B, where the clusters are initially oriented along the deformation direction, the deformation instead induces a permanent change in the cluster morphology. The Mullins effect, associated with the hysteresis loop (directly proportional to loss of elasticity) of the mechanical curves, is found to be more evident in case B. The thinner loop in case A is due to the pronounced reversibility of the changes, indicating an enhanced elasticity and more reinforcing properties. A full agreement between the structural evolution and the mechanical behaviour of the two different cases is observed.

Fig. 143: Correlation between scattering pattern evolution and stress-strain curves for two different initial orientations.

Hierarchical scattering function for silica- filled rubbers under deformation: effect of the initial cluster distribution, M. Staropoli (a), D. Gerstner (b), M. Sztucki (c), G. Vehres (d), B. Duez (b),

S. Westermann (b), D. Lenoble (a) and W. Pyckhout-Hintzen (d), Macromolecules, 52, 9735-9745 (2019); https://doi. org/10.1021/acs.macromol.9b01751. (a) Luxembourg Institute of Science and

Technology, Belvaux (Luxembourg) (b) Goodyear S.A, Colmar-Berg (Luxembourg) (c) ESRF (d) Forschungszentrum Jülich (Germany)

PRINCIPAL PUBLICATION AND AUTHORS

This work was financed by the FNR Luxembourg in collaboration with Goodyear S.A., Colmar-Berg, Luxembourg.