Exploring the Elastic Behavior of Core–shell Organic–Inorganic Spherical Particles by AFM Indentation Experiments

Abstract

Monodispersed polystyrene (PS)-silica core–shell composite particles were synthesized via the hydrolysis and condensation of tetraethoxysilane (TEOS) on PS colloids at acidic medium. The thickness of silica coating was controlled by the amount of the addition of TEOS during the shell growth process. Transmission electron microscopy results confirmed that a continuous amorphous network of homogenous coating of silica was formed on the PS colloids. After coating by silica, the particle diameter increased from ca. 221 nm for uncoated PS cores to ca. 243–286 nm for PS-silica composite particles observed by scanning electron microscopy, indicating that the silica shell thickness was 11–32 nm. The elastic behavior of the obtained products was investigated by means of atomic force microscopy. The elastic moduli of samples were calculated by fitting the retract curves in force-separation plots based on the Hertzian contact model. The average moduli were 4–8 GPa for the PS-silica composite particles which were much lower than the that of the pure silica (72–75 GPa) and closed to that of the PS cores (2.1 ± 0.5 GPa). The elastic moduli of the PS-silica hybrids increased with increasing of silica shell thickness, suggesting that the elasticity of the PS-silica composite particles might be attributed to the PS cores and the silica shell was stiffening the polymer cores. These results provide a basis for exploring the mechanical properties of core–shell PS-silica hybrids in the application of novel abrasives for chemical mechanical polishing.