Inertial migration of neutrally buoyant particles in superhydrophobic channels

Abstract

At finite Reynolds numbers particles migrate across flow streamlines to their equilibrium positions in microchannels. Such a migration is attributed to an inertial lift force, and it is well-known that the equilibrium location of neutrally-buoyant particles is determined only by their size and the channel Reynolds number. Here we demonstrate that the decoration of a bottom wall of the channel by superhydrophobic grooves provides additional possibilities for manipulation of neutrally-buoyant particles. It is shown that the effective anisotropic hydrodynamic slip of such a bottom wall can be readily used to alter the equilibrium positions of particles and to generate their motion transverse to the pressure gradient. These results may guide the design of novel inertial microfluidic devices for efficient sorting of neutrally-buoyant microparticles by their size.

Near-wall hydrodynamic slip triggers swimming state transition of micro-organisms

“…δ < l S . Researchers have found the significant role of the actual features of a superhydrophobic wall in influencing the motion of particles, both passive or self-propelled, when the particle is very close to the wall (Pimponi et al 2014;Hu et al 2015;Nizkaya et al 2015Nizkaya et al , 2020. On the other hand, molecular simulations have predicted that specially structured surfaces with nanometre scale roughness can also lead to superhydrophobicity (Lundgren, Allan & Cosgrove 2007;Yang, Tartaglino & Persson 2008;Koishi et al 2009;Daub et al 2010), a situation that broadens the applicability of the present research.…”

“…The air-liquid interfaces can be modelled as free-slip or partial-slip boundaries with high slip length. The effective hydrodynamic boundary condition at the fluid-solid interface can then be modelled as a uniform partial slippage with high slip length in micrometres (Choi & Kim 2006;Joseph et al 2006;Lee & Choi 2008;Asmolov et al 2013;Nizkaya et al 2015). The value of this apparent slip length can be fine-tuned according to the relevant surface properties, as reported in the relevant literature (Ybert et al 2007;Asmolov et al 2013).…”

Instability of particle inertial migration in shear flow

“…In addition, we set the fluid density ρ = 1. Further implementation details are provided in our previous publications 23,[25][26][27][28][29] .…”

Inertial migration of oblate spheroids in a plane channel

“…Spheroids are are discretized on the fluid lattice and implemented as moving no-slip boundaries following the pioneering work of Ladd 14 . Details of our implementation can be found in our previous publications 7,[27][28][29][30][31] .…”