Evidence of the Transition from a Flexible to Rigid Percolating Network in Polymer Nanocomposites
Hung K. Nguyen, K. Nakajima
Abstract
The formation of a percolating filler network (PFN) in polymer nanocomposites is critical in explaining the substantial improvement of their mechanical properties in comparison to neat polymer systems. However, the structural mechanism underlying the formation and development of the PFN has remained under active debate. Here, we report a direct observation of microstructure development of the PFN in a model isoprene rubber filled with various nanoparticle fractions by means of nanoscale loss tangent (tan δ) imaging with amplitude-modulated atomic force microscopy. Tanδ imaging revealed, for the first time in real space, the formation of a flexible PFN when the filler volume fraction was increased to ∼16%, which subsequently developed to a rigid PFN at the fraction of ∼24%. Importantly, the observed transition agrees well with a marked increase in the mechanical reinforcement in macroscopic measurements.