Abstract
We determine both experimentally and numerically the onset of elastic flow instabilities in viscoelastic polymer solutions with different levels of shear thinning. Previous experiments realized in microfluidic serpentine channels using dilute polymeric solutions showed that the onset of elastic instabilities strongly depends on the channel curvature. The scaling dependence is well captured by the general instability scaling criterion proposed by Pakdel and McKinley [Phys. Rev. Lett., 1996, 76, 2459:1-4]. We determine here the influence of fluid shear thinning on the onset of such purely-elastic flow instabilities. By testing a set of polyethylene oxide solutions of high molecular weight at different polymer concentrations in microfluidic serpentine channels we observe that shear thinning has a stabilizing effect on the microfluidic flow. Three-dimensional numerical simulations performed using the White-Metzner model predict similar trends, which are not captured by a simple scaling analysis using the Pakdel-McKinley criterion.
Highlights
We determine both experimentally and numerically the onset of elastic flow instabilities in viscoelastic polymer solutions with different levels of shear thinning
The vast majority of viscoelastic fluids, both in nature and synthetic fluids used in different industries, often display strong shear thinning of the shear viscosity, especially at high shear rates
The shear rheology of dilute and semi-dilute PEO polymer solutions is reasonably well captured by the White–Metzner constitutive equation
Summary
We determine both experimentally and numerically the onset of elastic flow instabilities in viscoelastic polymer solutions with different levels of shear thinning. Flow kinematics in order to better understand the physical mechanisms at play, and from a practical standpoint as such instabilities are generally undesirable in viscometric measurements (and usually preclude the determination of material properties above their onset). Such instabilities occur in industrial applications, e.g. polymer extrusion or ink jet printing, and a good theoretical understanding and the ability to control their onset is of wide relevance. The aim of the current paper is to extend this analysis to incorporate more realistic rheology, shear-thinning effects
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