Quantitative characterization of high molecular weight polymer solutions in microfluidic hyperbolic contraction flow

Abstract

Nonlinear flows of polyacrylamide (PAAm) ( $$M_{\text{w}} = 5.7 \times 10^{6}\,{\text{g}}/{\text{mol}}$$ ) aqueous solutions through a micro-fabricated, hyperbolic contraction geometry with high Hencky strain ( $$\varepsilon_{{\text{H}}} = 3.7$$ ) have been characterized by micro-particle image velocimetry ( $$\mu $$ -PIV). Various flow dynamics regimes in a range of Weissenberg number (Wi) and Reynolds number (Re) are presented in a Wi–Re diagram. The symmetric corner vortices are only observed in the flow of low concentration PAAm solution ( $$c/c^{*}=3.3$$ ). In a higher concentration ( $$c/c^{*}=8.3$$ ), PAAm solution exhibits chaotic-like flow patterns in the strong nonlinear flow regime ( $$Wi>350$$ ). Extensional deformation in nonlinear flows of Wi up to 860 has been analyzed. Furthermore, the local stretch experienced by the polymer chain in complex flow is systematically quantified and linked to the corresponding velocity vector fields, which are valuable for understanding the highly nonlinear flow phenomena.