Résumé:

Silica-filled styrene-butadiene nanocomposites with polymer molecules grafted on industrial silica have been formulated for various silica volume fractions (≈ 10% and 20%v), chain masses (40 – 280 kg.mol-1), and fractions of graftable chains (0 – 100%). The silica structure was analyzed using electron microscopy and small-angle x-ray scattering. The nominal density of grafted molecules per unit silica surface ρD3, which depends on all three aforementioned parameters, covered a domain from 0 to about 0.1 nm-2. By comparing the filler structures at fixed grafting density (so-called ‘twins’), a surprising match of the microstructures was evidenced. A quantitative tool expressing the similarity of structures in reciprocal space is proposed. By comparing it to typical structural evolutions of this nanocomposite system, the match is unambiguously proven. Dynamical mechanical analysis was used to compare the mechanical properties of the twins. The viscoelastic plateau modulus is determined by ρD3 at high volume fractions, and found to be close for twins. This highlights the possibility to set the structure and the modulus by ρD3, and then tune the terminal relaxation time of nanocomposites via the chain length at constant grafting density.