Lewis B. Tunnicliffe

Silica–rubber microstructure visualised in three dimensions by focused ion beam–scanning electron microscopy

A focused ion beam–scanning electron microscope (FIB–SEM) technique for three‐dimensional reconstruction and representation of material microstructures was applied to a silica‐filled synthetic rubber for the first time. Backscattered electron imaging allowed differentiation between rubber matrix, silica filler and zinc oxide (used as an activator for the sulphur vulcanisation reaction). Subsequent image processing allowed three‐dimensional isosurface model generation of the particulate structure within the rubber composite and separation of zinc oxide from the silica filler. The potential for development and application of this technique using finite element analysis modelling is also highlighted.

Reinforcement of Rubber and Filler Network Dynamics at Small Strains

Carbon black particulate reinforcement of rubber is examined in terms of linear viscoelasticity and the dynamics of the filler particle network. First, it is demonstrated that for the case of purely hydrodynamic reinforcement, the dynamics of the filled rubber are equivalent to those of the corresponding unfilled material. A breakdown in thermorheological simplicity is observed with the onset of filler networking in reinforced compounds. The dynamics of the filler network are initially examined by strain sweep/recovery experiments performed on uncrosslinked materials. The role of the surface activity of carbon black in defining the rate and magnitude of flocculation is explored and various models to describe this process are reviewed. The dynamics of carbon black filler networks in crosslinked materials are probed using small strain torsional creep experiments. Physical ageing (structural relaxation) of filled compounds at temperatures well above the glass transition temperature of the rubber matrix is observed and the ageing rate is found to scale with the level of filler networking in the various compounds. Physical ageing is the result of non-equilibrium, slow dynamics, which sheds light on the physical origin of the filler network. Furthermore, the implications of physical ageing of highly filled rubbers on typical linear viscoelastic time–temperature superposition experiments are discussed.