Colloidal particle deposition on microchannel walls, for attractive and repulsive surface potentials

Area of Science:

• Colloid and Surface Science
• Physical Chemistry
• Materials Science

Background:

• Surface interactions are governed by van der Waals forces and electrostatic charges.
• At low ionic strengths, the Debye layer hinders particle-surface proximity.
• High salt concentrations (above 0.1 M) typically screen surface charges, enabling van der Waals interactions.

Purpose of the Study:

• To investigate particle deposition mechanisms when surface charges are attractive (opposite zeta potential signs).
• To elucidate the interplay between electrostatic and van der Waals forces under varying ionic strengths.
• To understand how hindered diffusion affects particle collection at surfaces.

Main Methods:

• Microfluidic experiments to observe deposition dynamics.
• Theoretical modeling to describe interaction forces.
• Numerical simulations to quantify deposition rates.

Main Results:

• Contrary to expectations for repulsive charges, attractive charges increase particle deposition at low ionic strengths (larger Debye lengths).
• Deposition rates are controlled by van der Waals forces, but electrostatically assisted.
• A mechanism is proposed where electrostatic attraction mobilizes particles, followed by van der Waals adhesion.

Conclusions:

• Electrostatic attraction, combined with van der Waals forces, drives particle deposition at low ionic strengths when surface charges are opposite.
• This contrasts with the charge screening mechanism observed at high ionic strengths.
• The findings reveal distinct deposition pathways based on surface charge interactions and ionic strength.