Colloidal polymer composites: Are nano-fillers always better for improving mechanical properties?

Area of Science:

• Materials Science
• Polymer Science
• Colloid Science

Background:

• Colloidal polymer composites blend polymer particles with fillers for diverse applications.
• Hard fillers typically increase elastic modulus, but filler size effects on deformation and viscoelasticity are underexplored.
• The filler-to-polymer particle size ratio is hypothesized to be critical for composite properties.

Purpose of the Study:

• Investigate the influence of filler particle size on the large-strain deformation, fracture, and viscoelastic characteristics of polymer colloid composites.
• Determine how varying filler sizes affect mechanical properties like creep resistance and modulus.
• Correlate composite properties with microstructure and filler:polymer particle size ratios.

Main Methods:

• Prepared colloidal composites by blending soft polymer colloids with calcium carbonate fillers of four distinct sizes (70 nm to 4.5 μm).
• Assessed large-strain deformation, linear viscoelasticity, and creep at increasing filler volume fractions (ϕ_CC).
• Employed Weibull statistics for failure strain analysis and scanning electron microscopy for microstructural examination.

Main Results:

• Nanofillers induced brittle fracture at lower ϕ_CC compared to micrometer-sized fillers.
• For a given ϕ_CC, nanoparticles increased storage modulus and creep resistance.
• Composite properties correlated with microstructure, influenced by the filler:polymer particle size ratio; nanoparticles reinforced but also created brittleness.

Conclusions:

• Filler particle size critically influences colloidal composite mechanical behavior and fracture modes.
• Optimizing the filler:polymer particle size ratio allows tailoring of microstructure for enhanced reinforcement and creep resistance.
• While nanoparticles offer superior reinforcement, careful control is needed to mitigate induced brittleness.