Silica-Coated Core-Shell Structured Polystyrene Nanospheres and Their Size-Dependent Mechanical Properties

Area of Science:

• Materials Science
• Nanotechnology
• Mechanical Engineering

Background:

• Core-shell nanostructures offer tunable properties for advanced applications.
• Understanding the mechanical behavior of composite nanospheres is crucial for their integration into functional materials.

Purpose of the Study:

• To synthesize and characterize the mechanical properties of polystyrene/silica (PS/SiO2) core-shell nanospheres.
• To investigate the influence of silica shell thickness on the elastic modulus.
• To establish a core-shell model for predicting the elastic properties of PS/SiO2 nanospheres.

Main Methods:

• Synthesis of monodisperse PS/SiO2 composite nanospheres via a modified Stöber method.
• Nanoindentation using atomic force microscopy (AFM) in tapping and contact modes.
• Analysis of experimental data using Hertz and Johnson-Kendall-Roberts (JKR) contact models.

Main Results:

• Elastic moduli of PS/SiO2 nanospheres ranged from 4-40 GPa, significantly higher than PS nanospheres (∼3.4 GPa).
• The JKR model proved more suitable for determining the elastic modulus of PS/SiO2 nanospheres.
• The elastic modulus of the SiO2 shell approached a constant value (∼46 GPa) with increasing shell thickness.

Conclusions:

• A core-shell model effectively describes the relationship between elastic modulus and shell thickness in PS/SiO2 nanospheres.
• The mechanical properties are linked to the synthesis and growth mechanism, particularly the SiO2 shell formation.
• These findings guide the application of PS/SiO2 nanospheres in surface engineering, micro/nanomanufacturing, and lubrication.