Challenges and opportunities in complex materials: silica-reinforced elastomers

Small-angle light and X-ray scattering are used to study the morphology of reinforcing fillers in organic rubbers. The data, which extend over six orders of magnitude in length scale, reveal a complex morphology of the powders consisting of primary particles, aggregates and agglomerates. The fragility of the agglomerates is assessed by observation of partial agglomerate disruption after exposure to intense ultrasound. Upon incorporation into rubber by mechanical mixing, the agglomerates break down all the way to the aggregates. The results are used to outline opportunities to exploit the growth processes underlying the complex structure to optimize the morphology for composite applications. Soft agglomerates that easily break down to aggregates, for example, aid in dispersion of reinforcing fillers in rubbers. The high surface area of the primaries, on the other hand, can be used to adjust the interaction between the rubber and the filler in order to control dynamic mechanical response of the filled rubber.