Abstract
We propose a novel microfluidic fractionation concept suitable for neutrally buoyant micron-sized particles. This approach takes advantage of the ability of grooved channel walls oriented at an angle to the direction of an external electric field to generate a transverse electroosmotic flow. Using computer simulations, we first demonstrate that the velocity of this secondary transverse flow depends on the distance from the wall, so neutrally buoyant particles, depending on their size and initial location, will experience different lateral displacements. We then optimize the geometry and orientation of the surface texture of the channel walls to maximize the efficiency of particle fractionation. Our method is illustrated in a full scale computer experiment where we mimic the typical microchannel with a bottom grooved wall and a source of polydisperse particles that are carried along the channel by the forward electroosmotic flow. Our simulations show that the particle dispersion can be efficiently separated by size even in a channel that is only a few texture periods long. These results can guide the design of novel microfluidic devices for efficient sorting of microparticles.
Highlights
We propose a novel microfluidic fractionation concept suitable for neutrally buoyant micron-sized particles
Highly anisotropic periodic grooves in the Cassie state,[24,27] in which the texture is filled with gas, or the Wenzel state,[28,29] when liquid follows the topological variations of the surface, generally generate secondary flows transverse to the direction of the applied force. These textured walls have been already studied in combination with an electroosmotic flow when the grooves were perpendicular to the direction of an external field, and it has been shown that such a system demonstrates a rich set of properties that are determined by its geometry,[29] or the charge of the texture regions.[30,31]
We propose a novel concept of particle fractionation based on the electroosmotic flow in a channel with grooved walls
Summary
We propose a novel microfluidic fractionation concept suitable for neutrally buoyant micron-sized particles. We use the emerging anisotropy of the flow to divert particles of different sizes towards different streamlines, achieving a lateral segregation of a uniformly mixed colloidal suspension To study this system, we employ a hybrid lattice Boltzmann–molecular dynamics simulation method suitable for both charged[33,34] and uncharged systems.[35,36] To avoid the explicit simulations of charged electrolyte species,[11] we propose to apply a set of appropriate boundary conditions at the channel walls instead. This strategy critically reduces the numerical cost of our simulations which in turn makes it possible to illustrate our concept via a full-scale computer experiment involving a continuous fractionation of a particle suspension in a grooved microchannel
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