Elongation-Induced Segregation in Periodically Textured Microfluidic Channels

We numerically investigate the motion of elongated microparticles in microfluidic channels at low Reynolds numbers. In channels with smooth walls, asymmetric initial conditions -- including particle orientation and lateral position -- lead to continuous variations in particle trajectories, potentially exhibiting repeated behavior depending on the channel geometry and initial conditions. However, we find that introducing periodically textured walls induces alignment of the particle with the channel centerline within a specific range of texture wavelengths. This occurs as the textured pattern disrupts the uniformity of the flow, creating localized high-velocity nodes that repeatedly guide the particle toward the centerline as it moves downstream. Notably, the characteristic length scale over which this alignment forms reduces with increasing particle elongation and diverges with increasing Reynolds number. Our findings reveal that elongation-induced alignment can be leveraged for microfluidic filtering applications, enabling the efficient separation of microparticles based on their geometric properties. This work opens new avenues for designing microfluidic devices tailored for high-precision particle sorting, with broad implications for biomedical and industrial applications.