Determination of Elastic Modulus of Composite PS/CeO₂ Core-shell Microspheres by Atomic Force Microscope

Atomic force microscopy (AFM) was employed to probe the mechanical properties of polystyrene (PS) microspheres and composite PS/CeO₂ core-shell structured microspheres. On the basis of Hertz's theory of contact mechanics, compressive moduli were measured by analyzing force-displacement curves captured on the microsphere samples. The average elastic modulus of the PS microspheres (120 nm in diameter) was 2.8 GPa. The compressive modulus is slightly lower than the modulus of polystyrene bulk materials. The thickness of the CeO₂ shell had influence on the mechanical properties of composite microspheres. The modulus of the composite microspheres increased by increasing the thickness of the CeO₂ shell. When the CeO₂ shell thickness was 8, 12 and 16 nm, the average elastic modulus of the composite microspheres was 7.93, 8.25 and 10.67 GPa, respectively. It is found that the elastic modulus of the composite microsphere and PS core was close.