Controlling particle dynamics in dead-end channels via boundary effects

Abstract

Controlled particle transport in confined geometries is crucial for advancements in fields ranging from targeted drug delivery to environmental remediation. Diffusiophoresis (DP) has been demonstrated to be a unique method to enhance efficiency and directionality of particle delivery. However, its counterpart, diffusioosmosis (DO) has received less attention in particle manipulation. Here, we systematically investigate the coupling between diffusiophoresis and diffusioosmosis to actively control particle transport in microfluidic dead-end pores. By exploiting solute concentration gradients and wall zeta potentials \(\zeta_{\text{w}}\), we achieve precise manipulation of colloidal particles without external power sources. Validated by experimental results, our established theoretical framework unveiled the intricate dependence of diffusioosmotic mobility ($D_{DO}$) on wall zeta potential and solute property and identified parameter ranges to flip the sign of $D_{DO}$. Furthermore, we introduced the concept of a critical reversal position \( y^* \), the maximum transverse position where particles reverse direction within the dead-end pore, and proposed a scaling law and generated regime maps to characterize its dependence on critical parameters. These results provide essential insights for optimizing microfluidic designs for efficient particle transport. This work not only advances the fundamental understanding of electrokinetic phenomena in confined geometries, but also opens new avenues for designing passive, energy-efficient microfluidic systems for biomedical and environmental applications.