Surfactant effects on microfluidic extensional flow of water and polymer solutions

Abstract

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.

Bead-on-fibre morphology in shear-thinning flow

“…We note that Dacus et al. (2022) observed that Tween-20 can affect the rheology of XG solutions in water; however, we observe a negligible effect on the rheology of our glycerol–water solvents, likely due to their high glycerol concentration (cf. solutions 2–5 in table 1).…”

“…The solution was covered and placed on a magnetic stirrer for 24 h. Tween-20 (T20) surfactant (Sigma-Aldrich; CAS: 9005-64-5) was then added to the solution in concentrations 0.02-4 %w. We note that Dacus et al (2022) observed that Tween-20 can affect the rheology of XG solutions in water; however, we observe a negligible effect on the rheology of our glycerol-water solvents, likely due to their high Label Glycerol/water (%) φ (ppm) T20 (%) NaCl (%) σ (mN m −1 ) β (mPa s n ) n glycerol concentration (cf. solutions 2-5 in table 1).…”

Effects of vertical confinement on the flow of polymer solutions in planar constriction microchannels

“…The vortices in the XG solution are only slightly smaller than those in water, consistent with our recent observations. 26,34 In contrast, the vortices in the PEO solution are significantly smaller, which may again indicate the stronger impact of fluid elasticity than shear thinning on the expansion flow. It is, however, unclear to the authors why the vortices in the PAA solution, which is more shear thinning than the XG solution and more viscoelastic than the PEO solution, are not the smallest among the tested fluids.…”

“…on the contraction and/or expansion polymer flow. [18][19][20][21][22][23][24][25][26] In addition, many other papers have studied the effects of fluid rheological properties such as shear thinning/thickening and viscoelasticity. [28][29][30][31][32][33][34][35][36] The length and width of the contraction and/or expansion microchannels in previous studies are usually kept much larger than the depth constructing a pseudo-Hele-Shaw configuration.…”

“…on the contraction and/or expansion polymer flow. 18–26 In addition, many other papers have studied the effects of fluid rheological properties such as shear thinning/thickening and viscoelasticity. 28–36…”