Polymer-based device for efficient mixing of viscoelastic fluids

Abstract

We demonstrated rapid mixing of viscoelastic fluids in microchannels constructed based on polymethyl methacrylate. Viscoelastic mixing without diffusion was achieved with an effective mixing length of less than 5mm and a relatively fast flow rate. With an abrupt contraction microgeometry (8:1 contraction ratio), we mixed two different viscoelastic fluids experimentally at very low Reynolds numbers, but enormous Peclet and elasticity numbers. This special geometrical configuration triggers flow instability, leading to turbulent and efficient mixing. This flow regime has negligible inertia effects but significant elastic effects.

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

“…This resulted in a strong elastic flow instability observed downstream of the contraction and therefore an effective mixing of the two dissimilar viscoelastic liquids with negligible diffusion and inertial effects. 2,29 In addition, the lower rel for 0.8% PGW (see Fig. 4) provides further explanation for the slanted regime boundaries in Fig.…”

“…2,29 These instabilities result from the unequal relaxation of elastic stresses stored in the fluids, after severe stretching thru the contraction channel. 9,10 These instabilities can provide rapid microfluidic mixing at a short mixing length (< 5 mm).…”

“…9,10 These instabilities can provide rapid microfluidic mixing at a short mixing length (< 5 mm). 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.…”

Micromixer based on viscoelastic flow instability at low Reynolds number

“…The formation of these asymmetrical vortices based on empirical observations was discussed in our previous works. 15,16 Figure 4 presents the consecutive velocity fields of viscoelastic two-fluid flow at Q =10 ml/ h ͑De= 434.6 and Re= 0.02͒. Salient and large corner vortices with viscoelastic "whipping" at upstream of the contraction were evident.…”

“…15,16 We have reported our experimental observations of streak flow in silicon-glass microchip. 16 Our mixing experiments have very high values of elasticity numbers ͑a ratio of elastic to inertial forces of the system͒, which are approximately 932 and 5070.…”