Rolling, sliding and trapping of driven particles in square obstacle lattices

TL;DR

This study explores how magnetic microparticles move in a patterned obstacle environment, revealing a reversal in transport direction influenced by obstacle spacing, which impacts microfluidic and material design.

Contribution

It provides a systematic analysis of particle motion in structured environments, highlighting the interplay of forces that control transport direction and behavior.

Findings

Reversal of particle translation direction with decreasing obstacle spacing

Identification of shear-induced rolling versus pressure-driven sliding

Structured environments significantly influence microscale particle transport

Abstract

Transport phenomena in complex and dynamic microscopic environments are fundamentally shaped by hydrodynamic interactions. In particular, microparticle transport in porous media is governed by the delicate interplay between particle-substrate friction and pressure forces. Here, we systematically investigate the motion of externally driven rotating magnetic microparticles near a substrate patterned with a square lattice of cylindrical obstacles, a model porous medium. Remarkably, we observe a reversal in the direction of particle translation as obstacle spacing decreases, highlighting a sensitive competition between shear-induced forward rolling and pressure-driven backward sliding due to flow-field symmetry breaking. These results demonstrate the crucial role of structured environments in determining microscale active particle transport, offering novel strategies for microfluidic design, targeted cargo delivery, and tunable active materials.