Surfactant effects on microfluidic extensional flow of water and polymer solutions

Surfactants are often added to particle suspensions in the flow of Newtonian or non-Newtonian fluids for the purpose of reducing particle-particle aggregation and particle-wall adhesion. However, the impact on the flow behavior of such surfactant additions is often overlooked. We experimentally investigate the effect of the addition of a frequently used neutral surfactant, Tween 20, at the concentration pertaining to microfluidic applications on the entry flow of water and three common polymer solutions through a planar cavity microchannel. We find that the addition of Tween 20 has no significant influence on the shear viscosity or extensional flow of Newtonian water and Boger polyethylene oxide solution. However, such a surfactant addition reduces both the shear viscosity and shear-thinning behavior of xanthan gum and polyacrylamide solutions that each exhibit a strong shear-thinning effect. It also stabilizes the cavity flow and delays the onset of flow instability in both cases. The findings of this work can directly benefit microfluidic applications of particle and cell manipulation in Newtonian and non-Newtonian fluids. Published under an exclusive license by AIP Publishing.

Automated summary

The addition of the neutral surfactant Tween 20 has a weak influence on the flow behavior of water and homogeneous polymer solutions. It does not significantly affect the shear viscosity and extensional flow of Newtonian fluids, but reduces the shear viscosity and shear-thinning behavior of xanthan gum and polyacrylamide solutions with strong shear-thinning effects. The addition of Tween 20 also stabilizes the flow and delays flow instability.