STRUCTURE AND VISCOELASTICITY OF RUBBER MATERIALS

Highly filled elastomers are structured three-dimensionally viscoelastic materials formed through interfacial interactions between the rubbery matrix and the fine reinforcing particles such as carbon black and silica. There exist great disputes or contradictory research results about mechanisms of the formation (physical or chemical absorption) of bound rubber (BdR), molecular relaxation of the matrix, reinforcement (Einstein-Smallwood and Guth-Gold equations and their modified forms for isolated particles, dynamic cluster-cluster aggregation model for particle clusters, and rigidity percolation and jamming models for particle network) and nonlinear viscoelasticity (hypotheses in relation to destroying and rebuilding of particle-particle interaction, particle-rubber interaction, particle network and particle-rubber interpenetrating network) of highly filled rubbers in a long time. Nevertheless, the structure and dynamics heterogeneities, strain (strain rate) amplification effect introduced by presence of particles, and the interfacial interactions featured by the presence of a molecular dynamics gradient in the close vicinity around the particles become clear and well-accepted throughout the scientific researches more than one century. On the basis of summarizing some primary results involving influences of BdR on the macroscopic viscoelasticity of rubber materials, the authors propose two important research directions for rubber science in relation to their investigating the viscoelasticity of highly filled rubbers. The first one is to include the structure and dynamics heterogeneities in theories of reinforcement and nonlinear viscoelasticity and the second is to create relationships between microscopic effects (molecular relaxation on different time scales and particle dispersion on different spatial scales) and macroscopic properties for rubber materials via BdR or the particle-rubber gel in filled compounds.