arXiv subjects

Jinghui Gao

Publications and source records attributed to Jinghui Gao.

2 recordsLinked to original sources

arXiv2024

Sedimenting microrollers navigate saturated porous media

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.

cond-mat.soft↗

arXiv2023

Microrollers Flow Uphill as Granular Media

Pour sand into a container and only the grains near the top surface move. The collective motion associated with the translational and rotational energy of the grains in a thin flowing layer is quickly dissipated as friction through multibody interactions. Alternatively, consider what will happen to a bed of particles if one applies a torque to each individual particle. In this paper, we demonstrate an experimental system where torque is applied at the constituent level through a rotating magnetic field in a dense bed of microrollers. The net result is the grains roll uphill, forming a heap with a negative angle of repose. Two different regimes have been identified related to the degree of mobility or fluidization of the particles in the bulk. Velocimetry of the near surface flowing layer reveals the collective motion of these responsive particles scales in a similar way to flowing bulk granular flows. A simple granular model that includes cohesion accurately predicts the apparent negative coefficient of friction. In contrast to the response of active or responsive particles that mimic thermodynamic principles, this system results in macroscopic collective behavior that has the kinematics of a purely dissipative granular system.

cond-mat.soft↗