Viscoelastic properties and filler dispersion in carbon black‐filled and silica‐filled cross‐linked natural rubbers

The activation energies (Δ E J ′ and Δ E J ″ ) calculated from the temperature dependence of the storage compliance ( J ′) and the loss compliance ( J ″) of carbon black (CB)‐filled, hydrophobic silica‐ and hydrophilic silica‐filled cross‐linked natural rubbers (NRs) were found to be less than 15 kJ mol −1 , which corresponds to the physical range of van der Waals interaction. The results of three‐dimensional‐transmission electron microscopy measurements indicate that the closest distance ( d p ) between the two neighboring nanofiller aggregates centers decreased sharply with increasing nanofiller loading and tended to become constant at a nanofiller loading of around 30 phr or higher. For all samples examined, there were two regions related to the elastic deformation energy, and the critical d p value between the two regions was in the order of CB > hydrophobic silica = hydrophilic silica. Additionally, Δ E J ′ developed in the region of longer d p than that of Δ E J ″ . On the other hand, Δ E J ″ occurred after the formation of the filler network and was larger than Δ E J ′ . Δ E J ″ is assumed to be related to slippage of the junction and the rearrangement of the nanofiller network. Therefore, the dependence of Δ E J ′ and Δ E J ″ on d p suggests that the interaction layer between the nanofiller and NR has at least two energy levels. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2594–2602, 2013