Mixing with viscoelastic waves at low Reynolds numbers

Mixing at the microfluidic scale is challenging due to the low Reynolds numbers and often high Péclet numbers. Without turbulence, mixing relies solely on diffusion, resulting in slow and inefficient mixing. We demonstrate enhanced mixing in a simple Y-shaped microfluidic channel using viscoelastic turbulence in fluids containing macromolecules, such as DNA and polyethylene oxide. We investigated mixing at two distinct scales: the mixing of small molecules and the mixing of polymers. We show how the viscoelastic fluctuations fold the solvent, resulting in enhanced reaction rate between two reagents, as demonstrated by a mixed fraction of more than 75% between Fluo-3 and Ca²⁺ solutions in a few seconds. We also show how the viscoelastic turbulence enhances the mixing of the macromolecules, with a mixed fraction close to 65% between two DNA solutions. By harnessing viscoelastic turbulence, rapid mixing can be achieved in microfluidic channels where conventional turbulence cannot operate. The simplicity of our device fabrication further makes this approach a versatile, scalable, and easily integrated platform for applications ranging from chemical synthesis to biomedical diagnostics and assays.