Unraveling the Particle Morphology of ABS Polymer Latexes by 3D STEM

Acrylonitrile-butadiene-styrene (ABS) materials have a complex microstructure formed by a dispersion of grafted polybutadiene (PB) particles in a poly-(styrene-acrylonitrile) matrix (SAN). The grafting properties of the grafted PB particles are critical to achieving effective dispersion and compatibility with the SAN matrix in the compounded ABS material. Therefore, characterization of the particle morphology helps understand the polymerization mechanism, as well as the final properties of the ABS material. In this work, we utilize high angle annular dark-field scanning transmission microscopy (HAADF-STEM) tomography to determine the morphology of ABS polymer latex particles. Electron tomography (ET) 3D reconstruction of the whole particle allows determining quantitatively the volume fractions and distribution of each phase (internal SAN clusters, PB matrix, and SAN shell) in the latex particle. The information acquired in a single particle is used to illustrate that internal and external grafting properties can be determined accurately from microscopic analysis. The total grafting (internal plus external) agrees with the grafting properties measured experimentally by an extraction process.