Micromixer based on viscoelastic flow instability at low Reynolds number

Abstract

We exploited the viscoelasticity of biocompatible dilute polymeric solutions, namely, dilute poly͑ethylene oxide͒ solutions, to significantly enhance mixing in microfluidic devices at a very small Reynolds number, i.e., ReϷ 0.023, but large Peclet and elasticity numbers. With an abrupt contraction microgeometry ͑8:1 contraction ratio͒, two different dilute poly͑ethylene oxide͒ solutions were successfully mixed with a short flow length at a relatively fast mixing time of Ͻ10 s. Microparticle image velocimetry was employed in our investigations to characterize the flow fields. The increase in velocity fluctuation with an increase in flow rate and Deborah number indicates the increase in viscoelastic flow instability. Mixing efficiency was characterized by fluorescent concentration measurements. Our results showed that enhanced mixing can be achieved through viscoelastic flow instability under situations where molecular-diffusion and inertia effects are negligible. This approach bypasses the laminar flow limitation, usually associated with a low Reynolds number, which is not conducive to mixing.

Experimental observations of flow instabilities and rapid mixing of two dissimilar viscoelastic liquids

“…Peclet number (Pe) was also included to show the dominant transport phenomenon in such flow system. The same notations were used here as in our previous work, 2,3 that is all lengthscales and velocity terms are associated with the contraction channel, unless otherwise stated.…”

“…2,29 Furthermore, the unique advantage of this mixing technology is that the viscoelastic properties responsible for elastic flow instabilities could be readily found in most chemical and biological samples like organic and polymeric solutions, [23][24][25] blood 28 and crowded proteins and enzymes samples. 26,27 In this paper, we used the same microdevice previously reported 2,3 to experimentally show that the viscoelasticity ratio (between mainstream and sidestream liquids) has a direct bearing on the magnitude of the induced elastic flow instabilities, and in particular the transverse flow instability at downstream of a contraction. The possible underlying mechanism is discussed to elucidate the complex interplay between elasticity/viscosity and the elasticity ratio between the mainstream and side-streams solutions.…”

“…Furthermore, to exploit effectively the viscoelasticity of such liquids for elastic flow instability, abrupt and sharp convergent/divergent geometries should be employed. 3,7,8 It is known that rounded corners will compromise the elastic effects. 9,10 This is attributed to the stress singularities developed at the entry corners which have been well documented as the source of elastic instabilities in many macroscale experiments.…”

“…2 This approach would have the potential to disturb the liquid from its laminar regime and bypass the inherent small Re limitation. 3 Aqueous solutions of flexible polymers are viscoelastic. 4 The distinct characteristic of a viscoelastic liquid is its strong dependency of elastic stresses on the flow history.…”

An effective splitting-and-recombination micromixer with self-rotated contact surface for wide Reynolds number range applications

“…Passive micromixers 1, [8][9][10][11][12] do not require external energy but only depend on the structure of the channel, and the mixing mechanism relies entirely on molecular diffusion or chaotic advection. For achieving a high mixing efficiency, active micromixers usually utilize the disturbance induced by an external field, such as the electric field, [13][14][15][16] the acoustic field, [17][18][19][20] and the magnetic field, 21,22 etc.…”