Autostratification in drying colloidal dispersions: effect of particle interactions

Area of Science:

• Materials Science
• Physical Chemistry
• Colloid Science

Background:

• Vertical segregation of particles during film casting is a common issue, influenced by factors like particle size, charge, and drying rates (Peclet number).
• Previous models, such as Trueman et al.'s, have explored particle segregation, often simplifying chemical potential calculations.
• Understanding particle interactions is key to controlling particle distribution in thin films.

Purpose of the Study:

• To investigate the role of particle interactions in vertical segregation during film drying.
• To analyze the behavior of charged particles with varying and identical Peclet numbers.
• To experimentally validate theoretical predictions regarding particle segregation.

Main Methods:

• Numerical modeling of particle segregation, considering entropy-driven chemical potentials.
• Systematic variation of Peclet numbers and particle charges in theoretical models.
• Experimental casting of films with particles having Peclet numbers around unity.

Main Results:

• Particle interactions were shown to be a critical factor in vertical segregation, alongside the Peclet number.
• Theoretical models predicted distinct segregation behaviors for charged particles with different and same Peclet numbers.
• Experimental results aligned with theoretical predictions for systems where Peclet numbers straddled unity.

Conclusions:

• Particle interactions are a dominant factor in vertical segregation during film formation.
• The Peclet number and particle charge interplay significantly affects particle distribution.
• The study provides a validated framework for predicting and controlling particle segregation in thin films.