Surface Chemistry-based Continuous Separation of Colloidal Particles via Diffusiophoresis and Diffusioosmosis

TL;DR

This paper presents a microfluidic method using diffusiophoresis and diffusioosmosis to continuously separate colloidal particles based on surface chemistry, achieving high efficiency by exploiting differences in surface group concentrations.

Contribution

It introduces a novel microfluidic technique for continuous separation of colloids based on surface properties affecting zeta potential sensitivity, validated through experiments and theory.

Findings

Achieved 100% separation efficiency for particles with different surface groups.

Demonstrated the method's effectiveness with particles of similar size and zeta potential.

Proposed a simple device with broad applicability for surface property-based separation.

Abstract

The separation of colloidal particles based solely on their surface properties is a highly challenging task. This study demonstrates that diffusiophoresis and diffusioosmosis enable the continuous separation of carboxylate polystyrene particles with similar sizes and zeta potentials but distinct surface concentrations of carboxyl groups. The particles are exposed to salt concentration gradients generated in a double-junction microfluidic device. Through experimental and theoretical analyses, we demonstrate how the particle dynamics are influenced by their zeta potential sensitivity to the local salt concentration, which in turn is affected by surface conductance effects induced by the surface carboxyl groups. Consequently, colloids with comparable zeta potentials but differing surface concentrations of carboxyl groups can be separated with 100% efficiency. This approach, which employs a simple, easy-to-operate device, has discipline-spanning potential for the continuous separation of colloids distinguished solely by surface properties that influence their zeta potential sensitivities, like roughness, permeability, heterogeneity, and chemical composition.