Dynamics of a microroller under confinement

Rotating particles can translate when placed near a surface, forming microrollers with a wide range of biomedical and microfluidic applications.

In this work, we investigate the dynamics of microrollers in confined microchannels with different geometries by combining experiments, numerical simulations, and scaling analysis.

In constricted channels, we find that the translational velocity of a microroller decreases as it approaches the constricted region.

In both rectangular and cylindrical channels, velocity reversal occurs as the characteristic channel width decreases.

Using the force-free condition for free translation, we develop a systematic scaling framework that can be generalized to different channel geometries.

The scaling analysis yields functional dependences of the translational velocity on the degree of confinement, which agree well with both experiments and simulations.

Importantly, we demonstrate that the viscous stress generated by the far-field rotlet flow governs the observed velocity reduction and reversal, while the translational resistance resulting from the near-field shear flow suppresses translation under tight confinement.

The distinct roles of these flow components revealed by our analysis may provide practical guidance for controlling microroller dynamics in confined fluid environments.