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 was varied by adding graftable SB molecules. By comparing the filler structures at fixed ρ (so-called "twins"), a surprising match of the microstructures was evidenced. Mechanical measurements show that ρ 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.