Studying Twin Samples Provides Evidence for a Unique Structure-Determining Parameter in Simplifed Industrial Nanocomposites

The structure of styrene–butadiene (SB) nanocomposites filled with industrial silica has been analyzed using electron microscopy and small-angle X-ray scattering. The grafting density per unit silica surface ρ_<i>D</i>3 was varied by adding graftable SB molecules. By comparing the filler structures at fixed ρ_<i>D</i>3 (so-called “twins”), a surprising match of the microstructures was evidenced. Mechanical measurements show that ρ_<i>D</i>3 also sets the modulus: it is then possible to tune the terminal relaxation time of nanocomposites via the chain length while leaving the modulus and structure unchanged