Stratification Mechanism in the Bidisperse Colloidal Film Drying Process: Evolution and Decomposition of Normal...

Area of Science:

• Colloid science
• Materials science
• Statistical mechanics

Background:

• Colloidal films are widely used in various applications.
• Understanding their drying behavior is crucial for controlling film properties.
• Bidisperse systems exhibit complex stratification phenomena during drying.

Purpose of the Study:

• To investigate the relationship between normal stress evolution and microstructure formation during the drying of bidisperse colloidal films.
• To elucidate the mechanism behind small-on-top stratification using Brownian dynamics simulations.
• To analyze stress development at both global and particle length scales.

Main Methods:

• Brownian dynamics simulations were employed to model the drying process.
• Normal stress and microstructure evolution were tracked throughout the drying process.
• Analysis included global length scale stress quantification and particle length scale force decomposition.

Main Results:

• Small-on-top stratification is explained by the development of normal stress, particularly at high particle Péclet numbers (PeL).
• Normal stress localizes at the interface due to particle accumulation, increasing from the onset of drying.
• Microstructural analysis revealed stress evolution is linked to changes in particle contact distributions and local forces.

Conclusions:

• Normal stress development is a key factor driving stratification in drying bidisperse colloidal films.
• Particle-particle interactions, especially between small and large particles, significantly influence local forces and stratification.
• This study provides insights into the fundamental mechanisms governing drying and stratification in these complex systems.