Direct measurements of viscoelastic flows of DNA in a 2:1 abrupt planar micro-contraction

Gulati, Shelly; Müller, Susan; Liepmann, Dorian

doi:10.1016/j.jnnfm.2008.05.005

Cited by 53 publications

(62 citation statements)

References 55 publications

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“…In the case of backward flow, the results in terms of vortex size are qualitatively similar to forward flow, but for the higher Hencky strain geometry the vortices appear for lower values of De and these exhibit a more elongated shape. The increase of the vortex size with De is qualitatively different for the two polymers, with the growth regime for XG being qualitatively similar to that observed by Gulati et al 46 for a DNA solution ͑of concentration c =4c * , with c * being the overlap concentration͒ in flows through 2:1 abrupt contractions. Furthermore, despite the differences in geometry ͑Gulati et al 46 used a 2:1 abrupt contraction with a larger aspect ratio, i.e., a deeper microdevice͒, the range of vortex sizes reported by Gulati et al 46 is comparable to those obtained here with the XG solution.…”

Section: B Blood Analog Fluidssupporting

confidence: 79%

“…The increase of the vortex size with De is qualitatively different for the two polymers, with the growth regime for XG being qualitatively similar to that observed by Gulati et al 46 for a DNA solution ͑of concentration c =4c * , with c * being the overlap concentration͒ in flows through 2:1 abrupt contractions. Furthermore, despite the differences in geometry ͑Gulati et al 46 used a 2:1 abrupt contraction with a larger aspect ratio, i.e., a deeper microdevice͒, the range of vortex sizes reported by Gulati et al 46 is comparable to those obtained here with the XG solution. These similarities are rather interesting, and may be associated to the fact that both DNA and XG are rigid rod-like molecules.…”

Section: B Blood Analog Fluidssupporting

confidence: 79%

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Extensional flow of blood analog solutions in microfluidic devices

et al. 2011

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In this study, we show the importance of extensional rheology, in addition to the shear rheology, in the choice of blood analog solutions intended to be used in vitro for mimicking the microcirculatory system. For this purpose, we compare the flow of a Newtonian fluid and two well-established viscoelastic blood analog polymer solutions through microfluidic channels containing both hyperbolic and abrupt contractions/expansions. The hyperbolic shape was selected in order to impose a nearly constant strain rate at the centerline of the microchannels and achieve a quasihomogeneous and strong extensional flow often found in features of the human microcirculatory system such as stenoses. The two blood analog fluids used are aqueous solutions of a polyacrylamide ͑125 ppm w/w͒ and of a xanthan gum ͑500 ppm w/w͒, which were characterized rheologically in steady-shear flow using a rotational rheometer and in extension using a capillary breakup extensional rheometer ͑CaBER͒. Both blood analogs exhibit a shear-thinning behavior similar to that of whole human blood, but their relaxation times, obtained from CaBER experiments, are substantially different ͑by one order of magnitude͒. Visualizations of the flow patterns using streak photography, measurements of the velocity field using microparticle image velocimetry, and pressure-drop measurements were carried out experimentally for a wide range of flow rates. The experimental results were also compared with the numerical simulations of the flow of a Newtonian fluid and a generalized Newtonian fluid with shear-thinning behavior. Our results show that the flow patterns of the two blood analog solutions are considerably different, despite their similar shear rheology. Furthermore, we demonstrate that the elastic properties of the fluid have a major impact on the flow characteristics, with the polyacrylamide solution exhibiting a much stronger elastic character. As such, these properties must be taken into account in the choice or development of analog fluids that are adequate to replicate blood behavior at the microscale.

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Section: B Blood Analog Fluidssupporting

confidence: 79%

Section: B Blood Analog Fluidssupporting

confidence: 79%

Extensional flow of blood analog solutions in microfluidic devices

et al. 2011

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“…18,19 Flow instabilities in viscoelastic fluids are interesting dynamical phenomena and have potential applications in microfluidic devices where they can be utilized in flow control elements such as switches and diodes, 20,21 or exploited to produce efficient mixing at low Reynolds numbers. 22 In recent years considerable effort has been invested in trying to characterize and understand the "purely-elastic" flow instabilities that are observed at low Reynolds number in strong extensional flows of viscoelastic fluids in microfluidic capillary entrance flows [23][24][25][26][27][28][29] and also in conventionally shaped cross-slot devices. [30][31][32][33][34][35][36] Using a microfluidic cross-slot geometry, Poole et al 32 have advocated a buckling mechanism as the driving force behind the steady flow bifurcation, resulting from the compressive flow between the two inlet channels of the cross-slot.…”

Section: Introductionmentioning

confidence: 99%

Instabilities in stagnation point flows of polymer solutions

Haward

McKinley

2013

Physics of Fluids

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A recently-developed microfluidic device, the optimized shape cross-slot extensional rheometer, or OSCER [S.J. Haward, M.S.N. Oliveira, M.A. Alves and G.H. McKinley, Phys. Rev. Lett. 109, 128301 (2012)], is used to investigate the stability of viscoelastic polymer solutions in an idealized planar stagnation point flow. Aqueous polymer solutions, consisting of poly(ethylene oxide) and of hyaluronic acid with various molecular weights and concentrations, are formulated in order to provide fluids with a wide range of rheological properties. Semi-dilute solutions of high molecular weight polymers provide highly viscoelastic fluids with long relaxation times, which achieve a high Weissenberg number (Wi) at flow rates for which the Reynolds number (Re) remains low; hence the elasticity number El = Wi/Re is high. Lower concentration solutions of moderate molecular weight polymers provide only weakly viscoelastic fluids in which inertia remains important and El is relatively low. Flow birefringence observations are used to visualize the nature of flow instabilities in the fluids as the volume flow rate through the OSCER device is steadily incremented. At low Wi and Re, all of the fluids display a steady, symmetric and uniform 'birefringent strand' of highly oriented polymer molecules aligned along the outflowing symmetry axis of the test geometry, indicating the stability of the flow field under such conditions. In fluids of El > 1, we observe steady elastic flow asymmetries beyond a critical Weissenberg number, Wi crit , that are similar in character to those already reported in standard cross-slot geometries [e.g. P.E. Arratia, C.C. Thomas, J. Diorio and J.P. Gollub, Phys. Rev. Lett. 96, 144502 (2006)]. However, in fluids with El < 1 we observe a sequence of timedependent inertio-elastic instabilities beyond a critical Reynolds number, Re crit , characterized by high frequency spatiotemporal oscillations of the birefringent strand. By plotting the critical limits of stability for the various fluids in the Wi-Re operating space, we are able to construct a stability diagram delineating the distinct steady symmetric, steady asymmetric and inertio-elastic flow regimes in this idealized planar elongational flow device.

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“…The time-dependent three-dimensional flow that sometimes ensues following onset of a purely elastic flow instability can greatly enhance the mixing efficiency of a microfluidic device at small Reynolds number [25]. There have been few studies to date that have systematically investigated the dynamics associated with these elastic nonlinearities on the microscale [21,[26][27][28][29][30]. With microfluidic computing in mind, Groisman et al were the first to exploit elastic instabilities in designing a nonlinear fluid resistor, a bistable flip-flop memory element [28] and a flow rectifier [29].…”

Section: Introductionmentioning

confidence: 99%

Investigating the stability of viscoelastic stagnation flows in T-shaped microchannels

Soulages

Oliveira

Sousa

et al. 2009

Journal of Non-Newtonian Fluid Mechanics

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We investigate the stability of steady planar stagnation flows of a dilute polyethylene oxide (PEO) solution using T-shaped microchannels. The precise flow rate control and well-defined geometries achievable with microfluidic fabrication technologies enable us to make detailed observations of the onset of elastically-driven flow asymmetries in steady flows with strong planar elongational characteristics. We consider two different stagnation flow geometries; corresponding to T-shaped microchannels with, and without, a recirculating cavity region. In the former case, the stagnation point is located on a free streamline, whereas in the absence of a recirculating cavity the stagnation point at the separating streamline is pinned at the confining wall of the microchannel. The kinematic differences in these two configurations affect the resulting polymeric stress fields and control the critical conditions and spatiotemporal dynamics of the resulting viscoelastic flow instability. In the free stagnation point flow, a strand of highly-oriented polymeric material is formed in the region of strong planar extensional flow. This leads to a symmetry-breaking bifurcation at moderate Weissenberg numbers followed by the onset of three-dimensional flow at high Weissenberg numbers, which can be visualized using streak-imaging and microparticle image velocimetry. When the stagnation point is pinned at the wall this symmetry-breaking transition is suppressed and the flow transitions directly to a threedimensional time-dependent flow at an intermediate flow rate. The spatial characteristics of these purely elastic flow transitions are compared quantitatively to the predictions of two-dimensional viscoelastic numerical simulations using a single-mode simplified PhanThien-Tanner (SPTT) model.

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Direct measurements of viscoelastic flows of DNA in a 2:1 abrupt planar micro-contraction

Cited by 53 publications

References 55 publications

Extensional flow of blood analog solutions in microfluidic devices

Extensional flow of blood analog solutions in microfluidic devices

Instabilities in stagnation point flows of polymer solutions

Investigating the stability of viscoelastic stagnation flows in T-shaped microchannels

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