Filled elastomers: polymer chain and filler characterization by a SANS–SAXS approach

One of the important features of filled elastomers in general is the so-called strain amplification, or the enhancement of the local deformation of the rubbery matrix in comparison to the macroscopic deformation of the sample. This is due to the presence of the filler, taken as an indeformable substance, that changes the properties of the system, both macroscopically like the stiffnesss or the Young modulus, and microscopically like the local overstrain of chains. We used commercially interesting fillers, all of them based on silica particles showing different surface properties, while the rubbery matrix was a blend of protonated and deuterated polyisoprene (PI). We varied the filler volume fraction and the applied strain. First, we studied separately the two components of the composite, characterizing by X-ray and neutrons the filler, to use this information later in the extraction of the single chain scattering from SANS measurements. For a description of the microscopic deformation we rely on the previous finding on the unfilled network obtained using the tube model by Heinrich and Straube, modified and rewritten for SANS experiments on this kind of system.