Inertial Focusing of Spherical Particles: The Effects of Rotational Motion

TL;DR

This study investigates how rotational motion influences inertial focusing of spherical particles in microfluidic channels, revealing significant effects on particle positioning and offering insights for improved microfluidic device design.

Contribution

The paper demonstrates that particle rotation significantly affects inertial focusing positions, providing a new phenomenological model and detailed analysis of rotating versus non-rotating particles.

Findings

Rotating particles exhibit different focusing patterns compared to non-rotating ones.

Rotation-induced lateral lift force is significant and linearly related to rotation magnitude.

Distinct stable focusing positions are observed for rotating and non-rotating particles in microchannels.

Abstract

The identification of cells and particles based on their transport properties in microfluidic devices is crucial for numerous applications in biology and medicine. Neutrally buoyant particles transported in microfluidic channels, migrate laterally towards stable locations due to inertial effects. However, the effect of the particle and flow properties on these focusing positions remain largely unknown. We conduct large scale simulations with dissipative particle dynamics, demonstrating that freely moving particles exhibit significant differences in their focusing patterns from particles that are prevented from rotation. In circular pipes, we observe drastic changes in rotating versus non-rotating focusing positions. We demonstrate that rotation-induced lateral lift force is significant, unlike previously believed, and is linearly dependent on the rotation magnitude. A simple phenomenological explanation extending existing theories is presented, that agrees well with our numerical findings. In square ducts, we report four face-centered stable positions for rotating particles, in accordance with experimental studies on a range of Reynolds numbers 50 < Re < 200. However, non-rotating particles stay scattered on a concentric one-dimensional annulus, revealing qualitatively different behavior with respect to the free ones. Our findings suggest new designs for micro-particle and cell sorting in inertia-based microfluidics devices.