Effective modulus of particle-packing containing hard and soft particles

Area of Science:

• Materials Science
• Soft Matter Physics
• Colloid Science

Background:

• Drying colloidal films with hard particles crack due to capillary pressure.
• Buckling occurs in fast-drying drops of similar dispersions.
• Crack-free thickness depends on particle properties and packing.

Purpose of the Study:

• To measure the critical cracking thickness of drying colloidal films composed of mixed hard and soft elastic particles.
• To determine the effective modulus of these composite films.
• To correlate critical cracking thickness with the film's effective modulus.

Main Methods:

• Fabrication of colloidal films with varying ratios of hard and soft elastic particles.
• Measurement of critical cracking thickness during drying.
• Scanning electron microscopy (SEM) to analyze particle distribution.
• Nanoindentation technique for comparative modulus measurement.

Main Results:

• The effective modulus of the composite film was successfully extracted from critical cracking thickness measurements.
• The measured effective modulus trend aligned with nanoindentation results.
• Effective modulus values fell between theoretical limits predicted by the rule of mixtures.
• Particle segregation due to sedimentation was observed and linked to deviations from theoretical limits.

Conclusions:

• Critical cracking thickness provides a quantitative measure of the effective modulus of colloidal films.
• The behavior of mixed hard-soft particle systems can be understood by considering particle segregation.
• This work offers insights into controlling cracking and understanding mechanical properties in drying colloidal films.