Sedimenting microrollers navigate saturated porous media

TL;DR

This paper introduces magnetically responsive microrollers that actively navigate saturated porous media, significantly improving transport efficiency over passive particles by rolling and overcoming surface interactions.

Contribution

It develops and investigates Janus microrollers activated by magnetic fields, demonstrating enhanced transport through porous media compared to passive particles.

Findings

Transport increases by orders of magnitude with microrollers

Transport efficiency depends on concentration, rotation rate, and magnetic field strength

Periodic rotation minimizes energy input while maximizing transport

Abstract

Particle sedimentation through porous media is limited by the inability of passive material to overcome surface interactions and a tortuous network of pores. This limits transport, delivery, and effectiveness of chemicals used as reactants, nutrients, pesticides, or for waste remediation. This work develops magnetically responsive microrollers that navigate the complex interstitial network of porous matter. Rather than arresting on the upward facing surfaces of the pores, particles can roll and fall further, increasing transport by orders of magnitude. This work directly investigates Janus microrollers, activated by a rotating magnetic field, rolling and sedimenting though an index-matched porous medium. The mechanism of enhanced transport is determined, and the material flux is primarily a function of microroller concentration, rotation rate, and magnetic field strength. This mechanism is most efficient using a minimum number of rotations spaced out periodically in time to reduce the required energy input to greatly enhance transport. This general mechanism of transport enhancement can be broadly applied in numerous applications because the particles delivered within the porous matrix may be comprised of a wide variety of functional materials.