ASAXS, SAXS and SANS investigations of vulcanized elastomers filled with carbon black

Small-angle X-ray scattering (SAXS) performed down to small q values (q ≤ 10⁻³ Å⁻¹) is a powerful method for investigating the arrangement of filler aggregates in filled elastomers under uniaxial strain. Meanwhile, for vulcanized samples, zinc oxide is used as an additive. Owing to their high contrast, the ZnO particles remaining in the manufactured composite are strong X-ray scatterers. In the low-q domain, their scattering hides that of filler aggregates (carbon black, pyrogenic silica) and must be quantified in order to be suppressed. To this end, anomalous SAXS (ASAXS) and small-angle neutron scattering (SANS) have been performed. It is shown that ASAXS measurements can be performed down to small q values (q ≤ 10⁻³ Å⁻¹). Therefore ASAXS is well adapted to separate the contributions of ZnO and filler scattering. For neutron scattering the contrast of the ZnO particles is similar to that of carbon. Because the amount of ZnO is much smaller than that of filler, ZnO scattering can be neglected. Owing to multiple scattering effects, however, SANS can only be used for very thin samples (less than about 0.25 mm). It is shown that, providing multiple scattering is avoided, ASAXS and SANS yield similar scattering curves for the filler aggregates.