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

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 (Φ_silica), the number, size and branching degree of SiO₂ simultaneously increase (namely, self-agglomeration). Further increase Φ_silica, 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.