Multi - scale filler structure in simplified industrial nanocomposite silica / SBR systems studied by SAXS and TEM

Simplified silica (Zeosil 1165 MP) – SBR (140k carrying silanol end-groups) nanocomposites have been formulated by mixing of a reduced number of ingredients with respect to industrial applications. The thermo-mechanical history of the samples during the mixing process was monitored and adjusted to identical final temperatures. The filler structure on large scales up to microns was studied by transmission electron microscopy (TEM) and very small angle Xray scattering (SAXS). A complete quantitative model extending from the primary silica nanoparticle (of radius 10 nm), to nanoparticle aggregates, up to micron-sized branches with typical lateral dimension of 150 nm is proposed. Image analysis of the TEM-pictures yields the fraction of zones of pure polymer, which extend between the branches of a large-scale filler network. This network is compatible with a fractal of average dimension 2.4 as measured by scattering. On smaller length scales, inside the branches, small silica aggregates are present. Their average radius has been deduced from a Kratky analysis, and it ranges between 35 and 40 nm for all silica fractions investigated here (si = 8 – 21%v). A central piece of our analysis is the description of the inter-aggregate interaction by a simulated structure factor for polydisperse spheres representing aggregates. A polydispersity ha l-0 07 67 77 1, v er si on 1 20 D ec 2 01 2 Author manuscript, published in "macromolecules / J macromolecules 46, 1 (2013) 317-329" DOI : 10.1021/ma302248p