LINEAR VISCOELASTIC ENERGY DISSIPATION AT THE FILLER-RUBBER INTERFACE IN SILICA-RUBBER NANOCOMPOSITES
Event:182nd Technical Meeting Location: Cincinnati, OH Date: October 09, 2012 Author: Lewis B Tunnicliffe*, Alan G Thomas, Kevin E Young, John A Stuart and James J C Busfield Paper Number: 68
Understanding the reinforcement of rubber by particulate fillers has posed a challenge to academics and industrialists for many years. Whilst the stiffening of rubbers by rigid particulates is reasonably well understood in terms of the hydrodynamic effect and filler network dynamics, the understanding of the modification of a rubber's viscoelastic behaviour by the introduction of fillers remains incomplete.
Given the hydrodynamic assumption that there is no slippage of polymer at the filler-matrix interface, and that the dynamics of the matrix are homogeneous, at strains sufficiently small so as to not induce Fletcher-Gent (Payne) type non-linearities, such as filler structure breakdown, the viscoelastic response (tan8) of filled rubbers should be equal to that of the unfilled rubber. Experiments show that this assumption holds for rubbers filled with relatively large, spherical glass beads.
However, examining the very small strain viscoelastic properties of model precipitated silica-filled rubbers carefully developed to control experimental variables such as matrix crosslink density using custom built equipment we find this is no longer the case. A significant additional dissipation (Gil) can be measured. Interpretation of this dissipation as a physical mechanism can be based on concepts of polymer nano-confinement or polymer slippage at the interface. Nano confinement would present itself as a shift in the glass transition temperature of the polymer at the interface. Silanes which are used to improve adhesion of the polymer to the silica surface are examined and the resulting reduction in interfacial energy dissipation suggests that interfacial flow is the most likely cause of this additional viscoelastic dissipation in these composites. From creep test data within the linear-viscoelastic region over a range of temperatures, estimates of interfacial flow activation
energies are calculated.