Geometry-Driven Segregation in Periodically Textured Microfluidic Channels

Abstract

We investigate the transport dynamics of elongated microparticles in microchannel flows. While smooth-walled channels preserve the dependence of particle trajectories on initial orientation and lateral position, we show that introducing periodically textured walls can trigger robust alignment of the particle along the channel centerline. This geometry-driven alignment arises from repeated reorientations generated by spatially modulated shear gradients near the textured walls. The alignment efficiency depends on particle elongation and the relative texture wavelength, with an optimal range for maximal effect. While the observed alignment behavior is not limited to low Reynolds numbers, the characteristic alignment length scale diverges as the Reynolds number increases toward the turbulent flow regime. These findings offer a predictive framework for designing microfluidic devices that passively sort or focus anisotropic particles, with implications for soft matter transport, biophysical flows, and microfluidic engineering.

Figures (9)

• Figure 1: Sketch of the simulation setup. The particle's orientation $\theta(t)$ and lateral position $\lambda(t)$ generally change as the particle moves along the channel.
• Figure 2: Stationary center-of-mass velocity of a disk as a function of the pressure difference $\Delta P$, viscosity $\eta$, disk radius $R$, and lateral position $\lambda$. Default parameter values from Table I are used.
• Figure 3: Transit time $t\!_{_f}$ of a disk through the channel in terms of the pressure difference $\Delta P$, viscosity $\eta$, disk radius $R$, and lateral position $\lambda$. Default parameter values from Table I are used.
• Figure 4: Evolution of particle's lateral position and orientation in a smooth channel. (A) Orientation $\theta$ and center-of-mass distance from the centerline $\lambda$ as functions of the position $x$ along the channel axis for a particle with elongation $\kappa\,{=}\,0.1$ and $D_1\,{=}\,40\,\mu\text{m}$, $W{=}\,50\, \mu\text{m}$, and different initial conditions $\theta\!_{_0}$ and $\lambda_{_0}$. (B) Snapshots illustrating the motion of the particle starting with $\lambda_{_0}{=}\,0$ but $\theta\!_{_0}{\neq} \,0$. (C) Evolution of $\theta$ and $\lambda$ as a function of $x$ for $\theta\!_{_0}{=}\,0$ and varying values of $\lambda_{_0}$ and $\kappa$.
• Figure 5: (A) Transit time $t\!_{_f}$ and (B) stationary center-of-mass velocity $v_\text{c}^\text{st}$ of an ellipse as a function of the particle's initial orientation $\theta\!_{_0}$ and aspect ratio $\kappa$. Default parameter values from Table I are used.