The effect of interfacial dynamics on the bulk mechanical properties of rubber composites

The mechanical properties of rubber nanocomposites are believed to relate to the chain dynamics at the filler interface. Here, we tackle this hypothesis by combining traditional rheological measurements with our published results obtained by a modern technique of interfacial sensitive spectroscopy (Macromolecules 51:2180–2186, 2018). The complex shear modulus (G*) for silica (SiO2) nanoparticles filled with uncross-linked styrene-butadiene rubber (SBR) was studied as a function of the strain amplitude and temperature. In the case of the composite with a higher SiO2 fraction, G* remarkably decreased with increasing strain amplitude, known as the Payne effect. This phenomenon has been explained by the breakage of the filler network formed in the composite. Postulating that the G* difference between strain amplitudes of 0.1 and 20% (ΔG*) is a signature of the extent of how the filler network is broken, ΔG* was plotted against temperature. The decrement of ΔG* with increasing temperature changed at ~340 K. This temperature coincided with the temperature at which the chains in direct contact with the filler surface start to structurally relax. This coincidence was also observed for the SiO2-filled uncross-linked polyisoprene composite. Our results make it clear that the aforementioned hypothesis is likely for SiO2-filled uncross-linked rubber composites.