Customised bifurcating networks for mapping polymer dynamics in shear flows

Fidalgo, Joana and Zografos, Konstantinos and Casanellas, Laura and Lindner, Anke and Oliveira, Mónica S. N. (2017) Customised bifurcating networks for mapping polymer dynamics in shear flows. Biomicrofluidics, 11 (6). 064106. ISSN 1932-1058 (https://doi.org/10.1063/1.4989978)

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Abstract

Understanding the effect of varying shear stresses on individual polymer dynamics is important for applications such as polymer flooding, polymer induced drag reduction, or the design of DNA separation devices. In all cases, the individual polymer response to varying shear flows needs to be understood. A biomimetic design rule was recently proposed for bifurcating networks of rectangular channels of constant depth. These customised microfluidic geometries represent an elegant option to investigate, in a single device, multiple well-controlled shear stresses. Here, we present the first experimental realisation of such customised microfluidic networks, consisting of a series of rectangular microchannels with varying cross-sections, and we demonstrate their potential for testing polymer dynamics. We used microfluidic geometries optimised for both Newtonian and power-law fluids of constant or increasing average wall shear stress. The experimental model systems were tested using particle tracking velocimetry to confirm the theoretically predicted flow fields for shear-thinning xanthan gum solutions and a Newtonian fluid. Then, λ-DNA molecules were used as an example of shear sensitive polymers to test the effect of distinct shear stress distributions on their extension. By observing the conformation of individual molecules in consecutive channels, we demonstrate the effect of the varying imposed stresses. The results obtained are in good agreement with previous studies of λ-DNA extension under shear flow, validating the bifurcating network design. The customised microfluidic networks can thus be used as platforms for the investigation of individual polymer dynamics, in a large range of well-controlled local and cumulative shear stresses, using a single experiment.

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