Structuration of the Surface Layer during Drying of Colloidal Dispersions

Area of Science:

• Materials Science
• Colloid Science
• Surface Science

Background:

• Evaporative drying of colloidal dispersions is crucial for understanding porous media formation.
• The air-dispersion interface is key to consolidation mechanisms and final material properties.
• Drying-induced stress at the interface can lead to crack formation.

Purpose of the Study:

• To experimentally investigate the structural evolution at the air-dispersion interface during top-down drying of colloidal silica dispersions.
• To correlate particle structure with concentration at the drying front.
• To compare interfacial structural evolution with bulk behavior.

Main Methods:

• Specular neutron reflectivity to study the drying front structure.
• Small-angle neutron scattering for bulk dispersion analysis.
• Direct extraction of particle concentration from reflectivity and scattering data.

Main Results:

• Demonstrated the formation of a thick, concentrated surface layer at the drying front due to heterogeneous evaporation.
• Observed structural evolution from a sol to a wet-gel and particle aggregation preceding crust formation.
• Found similar structural evolution in the interface and bulk, with increased ordering for larger silica particles (5-13 nm radius).

Conclusions:

• Heterogeneous evaporation drives the formation of a concentrated surface layer during drying.
• Neutron reflectivity provides direct access to structure-concentration relationships at the drying interface.
• Particle size influences the degree of ordering during colloidal dispersion drying.