Revealing the three-dimensional filler structure in a rubber matrix based on fluorescein modified layered double hydroxides

Abstract

To gain insight into nonlinear viscoelastic behavior, e.g. the Payne effect, and in situ visualize the filler structure in a rubber matrix under strain, a methodology was developed to detect and track structural evolution based on fluorescent labeling. As a model system, layered double hydroxides (LDHs) with different lateral sizes (nanosheets and microsheets) were labeled with fluorescein (FLU) and then uniformly introduced into the rubber matrix through solution blending. The strain-induced deformation and destruction of the three-dimensional LDH filler structure were directly observed for the first time through laser scanning confocal microscopy (LSCM). The contributions of the breakdown of the filler network, strain softening of the glassy layer and macromolecular disentanglement to the Payne effect were qualitatively determined and analyzed in detail based on the structural information probed via LSCM together with transmission electron microscopy, rheometry and modulated differential scanning calorimetry. The primary mechanism for the Payne effect in this system was then proposed and the macromolecular disentanglement in the rubber matrix played a key role. Furthermore, the enhanced Payne effect with increasing LDH content was ascribed to the strain amplification effect induced by the filler network for the LDH nanosheet filled system and the chain sliding on orientated LDHs for microsheet filled compounds, respectively.