ABSTRACT
Many techniques and models have been already used in order to characterize the different reinforcement mechanisms. For instance, there are approaches which correspond to geometrical descriptions where fillers are the undeformable fraction of the sample together with occluded rubber and adsorbed immobilized elastomer layer (Litvinov and Steeman 1999). Strain amplification of elastomer matrix due to the presence of fillers has been quantify by small angle neutron scattering (Westermann et al., 1999) using a geometrical model (Guth and Gold) and the distribution of local strain has been model with a so-called ‘virtual rubber’ approach, based on spatial distribution of CB aggregates under strain reconstructed from 3D TEM observations (Akutagawa et al., 2008). Reinforcement has
1 INTRODUCTION
Elastomers present interesting mechanical properties for new applications, in particular when they are reinforced by solid particles or aggregates (fillers) of nanometric sizes like carbon black or silica (Wang 1998). They show strong reinforcement as measured by the ratio of the elastic modulus of the material to that of the unfilled matrix with a maximum at around gT + 20. Moreover, the elastic modulus in oscillatory measurements decreases strongly associated to increased dissipation, as the strain amplitude increases (the so-called Payne effect). Reinforcement is very complex involving different mechanisms related with the structure and dynamics at the molecular level (Kraus 1965): local strain amplification in the elastomer matrix due to filler volume effect, filler-filler network, filler-polymer interactions, and long-range modification of the molecular dynamics within the elastomer matrix, as the most important ones. In order to understand reinforcement effects it is
also been described by a double (or ‘super’) network model, in which a fraction of the elastomer chains tightly bound to fillers form a secondary, large-scale network of elastomer strands between fillers acting as crosslinks (Fukahori 2007).These mechanisms may play a role in the higher temperature range, but can certainly not account for the strong temperature variation of the mechanical properties, specifically the huge increase of reinforcement in the vicinity of the glass transition of the elastomer.
