Particle focusing and separation in xanthan gum solutions*

The passive manipulation of particles in viscoelastic fluids has received an increasing interest in the microfluidics community for the past decade. It exploits the flow-induced elastic lift and as well inertial lift (if the Reynolds number is not small) to focus particles toward size- and shape-dependent equilibrium positions. Such a continuous separation has thus far been demonstrated in viscoelastic fluids with a negligible or weak shear-thinning effect. We present in this work a systematic experimental study of the fluid shear-thinning effect on particle focusing and separation in weakly elastic xanthan gum solutions through straight rectangular microchannels. The effects of xanthan gum concentration and channel depth are examined for particle focusing and separation under varying flow rates.