A. Mujtaba, S. Ilisch, H.-J. Radusch, M. Beiner, T. Thurn-Albrecht, K. Saalwächter.
Detection of Surface-Immobilized Components and Their Role in
Viscoelastic Reinforcement of Rubber−Silica Nanocomposites.
ACS Macro. Lett. 3, 481-485 (2014).
Immobilized polymer fractions have been claimed
to be of pivotal importance for the large mechanical reinforcement
observed in nanoparticle-filled elastomers but remained elusive in
actual application-relevant materials. We here isolate the additive
filler network contribution to the storage modulus of industrial
styrene-butadiene rubber (SBR) nanocomposites filled with silica
at different frequencies and temperatures and demonstrate that it is
viscoelastic in nature. We further quantify the amount of
immobilized polymer using solid-state NMR and establish a
correlation with the mechanical reinforcement, identifying a direct,
strongly nonlinear dependence on the immobilized polymer
fraction. The observation of a temperature-independent filler percolation threshold suggests that immobilized polymer fractions
may not necessarily form contiguous layers around the filler particles but could only reside in highly confined regions between
closely packed filler particles, where they dominate the bending modulus of aggregated particles.