Effects of contraction ratio on non-linear dynamics of semi-dilute, highly polydisperse PAAm solutio

Highly non-linear flows of semi-dilute ð3:3 6 c=c � 6 16:6Þ polyacrylamide (PAAm) aqueous solutions through three micro-fabricated 4:1:4, 8:1:8 and 16:1:16 contraction–expansion geometries have been investigated by micro-particle imaging velocimetry (l-PIV) and pressure drop measurements. A set of quantitative data for PAAm solutions are obtained from: Gel Permeation Chromatography (GPC) analysis; rheometric characterization using Vilastic-3 and piezoelastic axial vibrator (PAV) with frequency up to 6650 Hz for linear viscoelasticity measurements, and using a microfluidic device for the measurement of the nonlinear shear viscosity. With three different flow geometries, and a wide range of Elasticity numbers ð14:7 6 El 6 476:8Þ and Weissenberg numbers ð1:4 6 Wi 6 131:7Þ, different nonlinear flow regimes are identified and correlated to vortex growth mechanisms. Results of similar El flows were mapped in a contraction ratio – Wi diagram. We found that under a given flow geometry tuning El can either increase or decrease the stability of the nonlinear flow structures. In addition to Wi and Re, the viscoelastic flow phenomena are dependent on the contraction and aspect ratios of flow geometry, and also sensitive to the molecular weight distribution of polymer. These results are of significance to the further development of microfluidic technologies.

[1]  J. Crassous,et al.  Characterization of the viscoelastic behavior of complex fluids using the piezoelastic axial vibrator , 2005 .

[2]  Gareth H. McKinley,et al.  Elasto-capillary thinning and breakup of model elastic liquids , 2001 .

[3]  J. Odell,et al.  Flow of dilute to semi-dilute polystyrene solutions through a benchmark 8:1 planar abrupt micro-cont , 2010 .

[4]  A. Colin,et al.  Nonlocal effects in flows of wormlike micellar solutions. , 2008, Physical review letters.

[5]  F. Pinho,et al.  Benchmark solutions for the flow of Oldroyd-B and PTT fluids in planar contractions , 2003 .

[6]  R. Larson.  Instabilities in viscoelastic flows , 1992 .

[7]  Gareth H. McKinley,et al.  The inertio-elastic planar entry flow of low-viscosity elastic fluids in micro-fabricated geometries , 2005 .

[8]  S. Quake,et al.  Microfluidic Memory and Control Devices , 2003, Science.

[9]  Simon J. Haward,et al.  Non-linear dynamics of semi-dilute polydisperse polymer solutions in microfluidics: A study of a benchmark flow problem , 2011 .

[10]  J. Cooper-White,et al.  The importance of downstream events in microfluidic viscoelastic entry flows: Consequences of increasing the constriction length , 2010 .

[11]  K. Walters,et al.  Flow characteristics associated with abrupt changes in geometry in the case of highly elastic liquids , 1986 .

[12]  J. Cooper-White,et al.  Capillary Break-up Rheometry of Low-Viscosity Elastic Fluids , 2005 .

[13]  U. Perego,et al.  Simulation of the flow of fresh cement suspensions by a Lagrangian finite element approach , 2010 .

[14]  J. Cooper-White,et al.  Drop formation and breakup of low viscosity elastic fluids: Effects of molecular weight and concentration , 2006 .

[15]  K. Walters,et al.  Further remarks on the lip-vortex mechanism of vortex enhancement in planar-contraction flows , 1989 .

[16]  D. Beebe,et al.  A particle image velocimetry system for microfluidics , 1998 .

[17]  S. Wereley,et al.  Volume illumination for two-dimensional particle image velocimetry , 2000 .

[18]  Gareth H. McKinley,et al.  High shear rate viscometry , 2008 .

[19]  T. Schwartz,et al.  Crossover from the theta to the Excluded Volume Single Chain Statistics: New Experimental Evidences and a Modified Blob Model , 1980 .

[20]  Justin J. Cooper-White,et al.  The effects of chain conformation in the microfluidic entry flow of polymer–surfactant systems , 2009 .

[21]  S. C. Omowunmi,et al.  Modelling the three-dimensional flow of a semi-dilute polymer solution in microfluidics—on the effect of aspect ratio , 2010 .

[22]  Daniel R. Lester,et al.  Drop formation dynamics of constant low-viscosity, elastic fluids , 2002 .

[23]  Gareth H. McKinley,et al.  Role of the elasticity number in the entry flow of dilute polymer solutions in micro-fabricated contraction geometries , 2007 .

[24]  S. Wereley,et al.  PIV measurements of a microchannel flow , 1999 .

[25]  S. Muller,et al.  Direct measurements of viscoelastic flows of DNA in a 2:1 abrupt planar micro-contraction , 2008 .

[26]  Jun Kameoka,et al.  An electrospray ionization source for integration with microfluidics. , 2002, Analytical chemistry.

[27]  L. Walker,et al.  Effect of fluid relaxation time of dilute polymer solutions on jet breakup due to a forced disturbance , 2002 .