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Esteban F. Medina-Banuelos, Benjamin M. Marin-Santibanez, Jose Perez-Gonzales, Francisco Rodriguez-Gonzalez
Couette flow of a yield-stress fluid with slip as studied by Rheo-PIV
Appl. Rheol. 27:5 (2017) 53893 (11 pages)
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The Couette flow of a model yield-stress fluid with slip at the walls, a 0.12% Carbopol® 940 microgel, was analyzed in this
work by simultaneous rheometrical and particle image velocimetry measurements (Rheo-PIV). The Rheo-PIV technique was
first tested in the analysis of the Couette flow of a Newtonian fluid and then used to determine the velocity and shear rate
distributions of the microgel across gap. A reliable and full description of the different flow regimes occurring in the steady
Couette flow of yield-stress fluids with slip at the rheometer walls was obtained, which includes rigid body-like motion at
stresses below the yield one, rigid body-like motion and shear flow at stresses above the yield one, as well as pure shear flow
once the shear stress at the outer cylinder overcomes the yield value. Slip occurred at both cylinders, which were made up of
hydrophobic (inner) and hydrophilic (outer) materials, respectively. The slip velocity values measured at both walls increased
along with the shear stress and the trends of these dependencies deviated from the predictions of the hydrodynamic and elastohydrodynamic
lubrication mechanisms of slip in the flow of soft deformable particle dispersions [1]. Besides, the yield stress
was determined with good accuracy from the velocity profiles, as well as the location of the yielded and non-yielded regions
for each flow condition. Finally, the consistency of the obtained velocity profiles was tested by comparison with a theoretical
prediction for the Couette flow problem of a Herschel-Bulkley fluid without slip.
► Cite this publication as follows:
Medina-Banuelos EF, Marin-Santibanez BM, Perez-Gonzalez J, Rodriguez-Gonzales F: Couette flow of a yield-stress fluid with slip as studied by Rheo-PIV, Appl. Rheol. 27 (2017) 53893.
Gregorio Zacahua-Tlacuatl, Jose-Gonzalez, J. Javier Castro-Arellano, Heberto Balmori-Ramirez
Rheological characterization and extrusion of suspensions of natural zeolites
Appl. Rheol. 20:3 (2010) 34037 (10 pages)
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A rheological characterization and extrusion of aqueous suspensions of natural zeolites were carried out in this work.
Preparation of suspensions followed similar routes to those used for the colloidal processing of ceramic powders.The suspensions
were prepared at different volume fractions (v/v%) ranging from 5 to 61 v/v% for a pH value of 7. The suspensions
showed a Newtonian behavior for solid contents up to 20 v/v% and shear thinning at higher solid loads. For solid contents
above 35 v/v%, the suspensions exhibited hysteresis and a yield stress that growth exponentially with the solid load. The
appearance of a yield stress and its fast growing at relatively low solid concentration, as compared to other type of ceramic
suspensions, is attributed to several factors as inter-particle interactions, the presence of relatively large particles and to the
influence of their irregular morphology. Also, a breaking stress was measured for solid contents above 35 v/v%, which characterizes
a failure of the structure of the suspensions after yielding. This breaking stress determines the onset of slip flow of
the suspensions, which is interpreted in this work as a signal of good extrusion characteristics. Finally, inexpensive and free
of surface defects tubes were obtained from natural zeolites.
► Cite this publication as follows:
Zacahua-Tlacuatl G, Perez-Gonzalez J, Castro-Arellano JJ, Balmorii Ramirez: Rheological characterization and extrusion of suspensions of natural zeolites, Appl. Rheol. 20 (2010) 34037.
V. Pavlinek, P. Saha, K. Perez-Gonzalez, L. de Vargas, J. Stejskal, O. Quadrat
Analysis of the Yielding Behavior of Electrorheological Suspensions by Controlled Shear Stress Experiments
Appl. Rheol. 16:1 (2006) 14-18
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The yielding behavior of two model electrorheological suspensions of uncoated silica particles and silica coated
with polyaniline base in silicone oil using controlled shear rate and controlled shear stress experiments has
been analyzed. The results demonstrate that unlike the uncertain dynamic yield stress values estimated from
the results obtained in the former mode by extrapolation of the unsteady shear stresses to zero shear rate, the
controlled shear stress measurement permits to detect sensitively the region starting from the initial rupture
of particle chain structure in the electric field at rest corresponding to a static yield stress and ending in total
breakage of suspension structure at a breaking stress. The latter quantity can be detected with a good accuracy
and proved to be a reliable criterion of the stiffness of electrorheological (ER) structure.
► Cite this publication as follows:
Pavlinek V, Saha P, Perez-Gonzalez J, DeVargas L, Stejskal J, Quadrat O: Analysis of the Yielding Behavior of Electrorheological Suspensions by Controlled Shear Stress Experiments, Appl. Rheol. 16 (2006) 14.
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