Lubricated extensional flow of viscoelastic fluids in a convergent microchannel

Abstract

Some of the fluids routinely used in microfluidic devices have micro and nanostructures that can generate viscoelastic behavior. In this paper, an experimental technique is developed to estimate the extensional flow resistance of dilute polymer solutions using flow in a lubricated, converging, and microfluidic channel. The channel has a two-dimensional hyperbolic profile, and the viscous or viscoelastic core fluid is lubricated by a less viscous Newtonian fluid that is introduced through side channels upstream. Differences in flow patterns are observed between miscible and immiscible lubricants. Stable flows are achieved with an immiscible lubricant and with a suitable interfacial tension between the core fluid and the lubricant. Steady extensional flows are established at low Reynolds numbers (Re ≪ 1 for the core fluid), at moderate Hencky strains (3 < ɛH < 3.9), and over a wide range of Deborah numbers (0 < De < 20). Pressure drop and flow rate measurements are made, and the velocity field is characteri...