Quantifying 3D-nanosized dispersion of SiO2 in elastomer nanocomposites by 3D-scanning transmission electron microscope (STEM)

Abstract

Nanofiller/elastomer nanocomposites as strategically important materials have attracted intensive attentions due to high elasticity. However, due to the limitation of conventional two-dimensional characterization methods, the multi-scaled dispersion structure of nanofiller in elastomer nanocomposites hasn’t been comprehensively understood. Here, we established a highly-objective method to comprehensively quantify the three-dimensional (3D)-dispersion of nanoparticle in elastomer matrix. 3D-scanning transmission electron microscope (STEM) was applied to get the intrinsic 3D-dispersion structure of nano-silica (SiO2) in solution-polymerized styrene-butadiene rubber (SSBR). Equivalent sphere and fractal branch models were created to further quantify the poly-dispersity, inner connectivity and morphology of SiO2. A two-stage agglomeration evolution schematic was proposed to elucidate the development of nanosized dispersion structure of SiO2. With the increase of SiO2 volume fraction (Φsilica), the number, size and branching degree of SiO2 simultaneously increase (namely, self-agglomeration). Further increase Φsilica, adjacent SiO2 interconnect with each other, leading to sharp increases of connectivity and branching degree of SiO2 (namely, external agglomeration). This two-stage agglomeration mode interprets the well-known “Payne effect” well, which has not been quantified by 3D dispersion structure parameters before.