Abstract
.Staggered and linear multi-particle trains constitute characteristic structures in inertial microfluidics. Using lattice-Boltzmann simulations, we investigate their properties and stability, when flowing through microfluidic channels. We confirm the stability of cross-streamline pairs by showing how they contract or expand to their equilibrium axial distance. In contrast, same-streamline pairs quickly expand to a characteristic separation but even at long times slowly drift apart. We reproduce the distribution of particle distances with its characteristic peak as measured in experiments. Staggered multi-particle trains initialized with an axial particle spacing larger than the equilibrium distance contract non-uniformly due to collective drag reduction. Linear particle trains, similar to pairs, rapidly expand toward a value about twice the equilibrium distance of staggered trains and then very slowly drift apart non-uniformly. Again, we reproduce the statistics of particle distances and the characteristic peak observed in experiments. Finally, we thoroughly analyze the damped displacement pulse traveling as a microfluidic phonon through a staggered train and show how a defect strongly damps its propagation.Graphical abstract
Highlights
Same-streamline pairs quickly expand to a characteristic separation but even at long times slowly drift apart
We reproduce the statistics of particle distances and the characteristic peak observed in experiments
Since the discovery of inertial focusing by Segre and Silberberg [1], inertial microfluidics has evolved into a mature research field with immense potential for biomedical applications [2,3,4]
Summary
Since the discovery of inertial focusing by Segre and Silberberg [1], inertial microfluidics has evolved into a mature research field with immense potential for biomedical applications [2,3,4]. At higher densities particles do move to an equilibrium position in the channel cross section and form regular trains along the channel axis [5,6,7] This feature of inertial microfluidics is particular useful for counting [8,9,10], sorting [11,12,13,14], or manipulating cells [15, 16]. While trains of particles were already observed by Segre and Silberberg [1], the first systematic analysis was done by Matas et al about 40 years later [17] This triggered further research on particle trains, which we describe below, in order to understand their occurrence more thoroughly. In this paper we contribute with our simulation study to the understanding of staggered and linear multi-particle trains including particle pairs (see fig. 1)
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