Rheology of vesicle suspensions under combined steady and oscillating shear flows

2012 ◽  
Vol 700 ◽  
pp. 362-381 ◽  
Author(s):  
A. Farutin ◽  
C. Misbah
Keyword(s):  
Shear Rate ◽  
Linear Response ◽  
Complex Fluids ◽  
Flow Direction ◽  
Complex Viscosity ◽  
Phenomenological Theory ◽  
Main Axis ◽  
Viscous Effects ◽  
Constant Shear ◽  
Microscopic Features

AbstractViscoelastic properties of complex fluids are usually extracted by applying an oscillatory shear rate ($\dot {\gamma } = \ensuremath{\alpha} {\dot {\gamma } }_{0} \cos (\omega t), $ where $\ensuremath{\alpha} {\dot {\gamma } }_{0} $ is a constant which is small for a linear response to make sense) to the fluid. This leads to a complex effective viscosity where its real part carries information on viscous effects while its imaginary part informs us on elastic properties. We show here theoretically, by taking a dilute vesicle suspension as an example, that application of a pure shearing oscillation misses several interesting microscopic features of the suspension. It is shown that if, in addition to the oscillatory part, a basic constant shear rate is applied to the suspension (so that the total shear rate is $\dot {\gamma } = {\dot {\gamma } }_{0} (1+ \ensuremath{\alpha} \cos \omega t)$, with ${\dot {\gamma } }_{0} $ a constant), then the complex viscosity reveals much more insightful properties of the suspension. First, it is found that the complex viscosity exhibits a resonance for tank-treading vesicles as a function of the frequency of oscillation. This resonance is linked to the fact that vesicles, while being in the stable tank-treading regime (with their main axis having a steady orientation with respect to the flow direction), possess damped oscillatory modes. Second, in the region of parameter space where the vesicle exhibits either vacillating-breathing (permanent oscillations of the main axis about the flow direction and breathing of the shape) or tumbling modes, the complex viscosity shows an infinite number of resonances as a function of the frequency. It is shown that these behaviours markedly differ from that obtained when only the classical oscillation $\dot {\gamma } = \ensuremath{\alpha} {\dot {\gamma } }_{0} \cos (\omega t)$ is applied. The results are obtained numerically by solution of the analytical constitutive equation of a dilute vesicle suspension and confirmed analytically by a linear-response phenomenological theory. It is argued that the same type of behaviour is expected for any suspension of soft entities (capsules, red blood cells, etc.) that exhibit periodic motion under constant shear flow. We shall also discuss the reason why this type of behaviour could not have been captured by existing constitutive laws of complex fluids.

scholarly journals Aging, Rejuvenation and Thixotropy in Complex Fluids: Time-dependence of the Viscosity at Rest and under Constant Shear Rate or Shear Stress

2008 ◽  
Vol 18 (5) ◽  
pp. 53298-1-53298-13
Author(s):  
Daniel Quemada
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Volume Fraction ◽  
Complex Fluids ◽  
Transient Behaviour ◽  
Volume Fractions ◽  
Constant Shear ◽  
Constant Shear Stress ◽  
Constant Shear Rate ◽  
Viscosity Changes

Abstract Complex fluids exhibit time-dependent changes in viscosity that have been ascribed to both thixotropy and aging. However, there is no consensus for which phenomenon is the origin of which changes. A novel thixotropic model is defined that incorporates aging. Conditions under which viscosity changes are due to thixotropy and aging are unambiguously defined. Viscosity changes in a complex fluid during a period of rest after destructuring exhibit a bifurcation at a critical volume fraction ϕc2. For volume fractions less than ϕc2 the viscosity remains finite in the limit t →∞. For volume fractions above critical the viscosity grows without limit, so aging occurs at rest. At constant shear rate there is no bifurcation, whereas under constant shear stress the model predicts a new bifurcation in the viscosity at a critical stress σB, identical to the yield stress σy observed under steady conditions. The divergence of the viscosity for σ≤σB is best defined as aging. However, for σ > σB, where the viscosity remains finite, it seems preferable to use the concepts of restructuring and destructuring, rather than aging and rejuvenation. Nevertheless, when a stress σA(≤σB) is applied during aging, slower aging is predicted and discussed as true rejuvenation. Plastic behaviour is predicted under steady conditions when σ > σB. The Herschel-Bulkley model fits the flow curve for stresses close to σB, whereas the Bingham model gives a better fit for σ >> σB. Finally, the model’s predictions are shown to be consistent with experimental data from the literature for the transient behaviour of laponite gels.

scholarly journals Computer aided optimisation of a constant shear-rate micro-channel contraction

2009 ◽  
Vol 50 ◽  
pp. 1004
Author(s):  
Simon Higgins ◽  
Gregory J Sheard ◽  
Andreas Fouras ◽  
Kerry Hourigan
Keyword(s):  
Shear Rate ◽  
Micro Channel ◽  
Constant Shear ◽  
Computer Aided ◽  
Constant Shear Rate

scholarly journals Patient-Specific Adhesion of Sickle Red Blood Cells in Shear-Gradient Microscale Flow

Blood ◽  
2017 ◽  
Vol 130 (Suppl_1) ◽  
pp. 964-964
Author(s):  
Erdem Kucukal ◽  
Jane A. Little ◽  
Umut A. Gurkan
Keyword(s):  
Shear Rate ◽  
Blood Cell ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Flow Direction ◽  
Patient Specific ◽  
Shear Rates ◽  
Microscale Flow ◽  
Shear Gradient ◽  
Equity Ownership

Abstract The pathophysiology of sickle cell disease (SCD) involves altered biophysical properties of red blood cells (RBCs) and increased cellular adhesion, which can synergistically trigger recurrent and painful vaso-occlusive events in the microcirculatory network. RBC adhesion to the endothelial wall is heterogeneous and may initiate such occlusions by disrupting the local flow thus activating platelets and promoting subsequent cell-cell interactions. Moreover, these episodic events take place within a wide range of dynamically changing shear rates at the microscale. In order to better understand the role of shear rate on this process, we quantified shear-dependent RBC adhesion to endothelial proteins fibronectin (FN) and laminin (LN) utilizing a microfluidic system that can simulate physiologically relevant shear gradients of microcirculatory blood flow at a single flow rate. Whole blood samples were collected from 20 patients (10 males and 10 females) with homozygous SCD (HbSS). Samples were perfused through FN and LN immobilized shear-gradient microchannels (Fig. 1A) in which the shear rate continuously changes along flow direction. Computational simulations characterized the flow dynamics near the adherent RBCs (Fig. 1B). Based on the numerical results, a rectangular "field of interest (FOI)", along which the shear rate dropped approximately three-fold, was chosen for quantification of shear-dependent RBC adhesion. We observed changes in RBC adhesion to LN and FN in the shear gradient flow. Figure 1C and 1D show typical adhesion curves of surface adherent RBCs for an individual SCD sample within the FOI. To assess patient specific shear-dependent adhesion, we defined a parameter, "shear dependent adhesion rate (SDAR)", which is the slope of the adhesion curves based on normalized RBC adhesion numbers. A higher SDAR value was indicative of marked numbers of adherent RBCs that detach at higher shear rates whereas the effect of shear rate on RBC detachment was less for a lower SDAR. We observed an inverse relationship between SDAR and number of persistently adherent RBCs at high shear rates. Shear-dependent RBC adhesion to LN was heterogeneous among SCD patients. Patients with higher WBC counts constituted the low SDAR population with a threshold SDAR value of 60 (Fig. 1E, p=0.005, ANOVA). WBCs from patients with higher SDARs (and fewer persistently adhered cells) were all within the normal range. Patients in the low SDAR group also had significantly elevated absolute neutrophil counts (Fig. 1F, p=0.006, ANOVA), and ferritin levels (Fig. 1G, p=0.007, ANOVA). The mean ferritin level of those with low SDAR was nearly ten times greater than normal (mean= [3272.3 ± 791.9] μg/L vs. [784.5±219.6] μg/L). No white blood cell (WBC) adhesion was observed in the experiments. Here, we report a novel shear dependent adhesion ratio of sickle RBCs utilizing LN and FN functionalized microchannels. The approach presented here enabled us to create a shear gradient throughout the channel which may simulate the physiological flow conditions in the post-capillary venules. We further analyzed shear-dependent RBC adhesion in a patient specific manner and identified patient groups with low and high SDAR. The findings also suggested a link between lower shear dependent sickle RBC adhesion to LN and patient clinical phenotypes including inflammation and iron overload. Acknowledgments: This work was supported by grant #2013126 from the Doris Duke Charitable Foundation, National Heart Lung and Blood Institute R01HL133574, and National Science Foundation CAREER Award 1552782. Figure 1: Shear-dependent sickle RBC adhesion in microscale flow. (A) Macroscopic image of the shear-gradient microchannel with the arrow indicating flow direction. (B) Velocity and shear rate contours on a 2D plane above the bottom surface. The dashed rectangular area indicates the field of interest (FOI) where the experimental data were obtained. (C, D) Typical distribution of adherent deformable and non-deformable RBCs in LN and FN functionalized microchannels with the shear gradient. Dashed lines represent the adhesion curves and the corresponding equations were used to quantify shear dependent adhesion data. Shear-dependent RBC adhesion was lower (nSDAR<60) in patients with elevated white blood cell counts (E), absolute neutrophil counts (F), and serum ferritin levels (G). The dashed rectangles indicate the normal clinical values. Figure 1 Figure 1. Disclosures Little: Hemex Health: Equity Ownership. Gurkan: Hemex Health: Employment, Equity Ownership.

Capillary Rheometry of Carbon-Black-Filled Butadiene—Acrylonitrile Copolymers

1975 ◽  
Vol 48 (4) ◽  
pp. 615-622 ◽  
Author(s):  
N. Nakajima ◽  
E. A. Collins
Keyword(s):  
Shear Rate ◽  
Carbon Black ◽  
Tensile Stress ◽  
Capillary Flow ◽  
Complex Viscosity ◽  
Appreciable Effect ◽  
Stress Strain ◽  
Capillary Rheometry ◽  
Strain Behavior ◽  
Acrylonitrile Copolymers

Abstract Capillary rheometry of carbon-black-filled butadiene—acrylonitrile copolymers at 125°C was performed over a wide shear rate range. The data were corrected for pressure loss in the barrel and at the capillary entrance, and for the non-Newtonian velocity profile (Rabinowitsch correction). No appreciable effect of pressure on viscosity was observed. The die swell values were very small, 1.1–1.4. This fact and the shape of the plots of shear stress vs. shear rate imply the presence of a particulate structure, which is probably built by carbon black surrounded with bound rubber. Unlike the behavior of raw amorphous elastomers, the steady-shear viscosity, the dynamic complex viscosity, and the viscosity calculated from tensile stress-strain behavior were significantly different from each other. That is, the capillary flow data indicated an alteration of the structure towards strain softening, and the tensile stress-strain behavior showed strain hardening, indicating retention of the structure up to the yield point. In the dynamic measurement, being conducted at very small strain, the structure is least disturbed. With unfilled elastomers essentially the same deformational mechanism was believed to be responsible in these three measurements, because the results can be expressed by a single master curve.

Therapeutic Amelioration of Vaso-Occlusion and Blood Flow Impairment in Transgenic Sickle Mice By the Antioxidant Flavonoid Quercetin

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4054-4054
Author(s):  
Sangeetha Thangaswamy ◽  
Henny H Billett ◽  
Craig A. Branch ◽  
Sandra M. Suzuka ◽  
Seetharama A Acharya
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Leukocyte Adhesion ◽  
Flow Direction ◽  
Radical Scavenging ◽  
Wall Shear Rate ◽  
Cremaster Muscle ◽  
Wild Type ◽  
Wall Shear

Abstract Sickle cell disease (SCD) is characterized by painful vaso-occlusive crises, which are, at least in part, due to an interaction of the sickle RBC (sRBC) with the vascular endothelium. Abnormal red blood cells (RBCs) impair blood flow and contribute to microcirculatory complications. Oxidative stress and/or oxidants generated via hemoglobin S (HbS) auto-oxidation play a vital role in the vaso-occlusive event in SCD. Antioxidant therapy mediated free radical scavenging and attenuation of oxidative stress may reduce red cell sickling and be beneficial for SCD. Several studies have described an antioxidant effect of flavonoids on the attenuation of free radical mediated biological membrane damage and the consumption of flavonoids reduces the prevalence of vascular diseases. Among flavonoids, quercetin (QUE) pentahydroxy flavone is the major representative. In vitro, QUE is a strong antioxidant with alkoxyl and peroxy radical scavenging ability. Due to the high susceptibility of sickle RBC to oxidation, QUE could be a useful therapy for SCD. Based on this concept, we examined the potential effect of QUE to improve microvascular function in a murine model of SCD. Methods: To confirm the protective effect of quercetin in vivo, we used Berkeley (Berk) sickle transgenic mice which express exclusively human α- and βS-globins with low levels of γ-globin (∼ 3-5%) generated by Paszty et al 1997. C57BL /6J were used as control wild type. We injected a single dose of QUE at different concentrations (50, 100, 200mg/kg body weight) intraperitoneally under normoxic conditions. Three hours after QUE administration, in vivo intra-vital microscopic observation of post-capillary venules in cremaster muscle was performed. The luminal diameters of the venules (∼ 20-40 µm diameter), centerline red blood cell velocity (Vrbc), adherent, emigrated and rolling leukocytes were measured by the technique described by Kaul et al 2004. Wall shear rate was calculated by Lipowsky et al, 1980. Results: QUE treatment restored blood flow, as evidenced by complete disappearance of vaso-occlusion in the postcapillary venules of Berk mice (Figure 1). However, no significant differences in venular diameter were noted with QUE treatment at any of the dose levels tested (50, 100, 200mg/kg) when compared to untreated Berk and wild type mice. But, when compared to untreated Berk mice, a significant increase in the RBC velocity was demonstrated in a dose dependent fashion (treated: 1.74 ±1.3 mm/sec, 3.02± 1.2 mm/sec, 3.4±0.90 mm/sec for 50, 100, 200 mg/kg dosing respectively vs. untreated 1.01± 1.05mm/sec, p<0.05). A dose of 200 mg level completely neutralized the vaso-occlusion. Increases in wall shear rate (650.01± 252.05 s-1 vs. 180.12± 165.02 s-1, p<6.03x10-6) was also observed in QUE treated vs. untreated Berk. This improvement of blood flow in the postcapillary venules correlated well with observed decreases in leukocyte adhesion (Figure 2A) and leukocyte emigration (Figure 2B) in QUE treated Berk mice (for doses 50, 100, and 200mg/kg) when compared to untreated Berk mice. Leukocyte rolling was also decreased for doses 100 and 200mg/kg (p<0.007, p<0.0002 respectively) after treatment with QUE when compared to untreated Berk and wild type. Figure 1: Representative images showing postcapillary venules in the cremaster muscle microcirculation of Berk mice compared to QUE treated and wild type. Black arrows indicate leukocytes and white arrows indicate the blood flow direction. Figure 1:. Representative images showing postcapillary venules in the cremaster muscle microcirculation of Berk mice compared to QUE treated and wild type. Black arrows indicate leukocytes and white arrows indicate the blood flow direction. Figure 2: Leukocyte adhesion (2A) and emigration (2B) in QUE treated Berk mice at 50, 100 and 200mg/kg doses compared to untreated Berk and wild type. Figure 2:. Leukocyte adhesion (2A) and emigration (2B) in QUE treated Berk mice at 50, 100 and 200mg/kg doses compared to untreated Berk and wild type. Figure 3 Figure 3. Conclusion: We observed an improvement in RBC velocity and wall shear rate, as well as a complete attenuation of leukocyte adhesion, rolling and emigration at the highest dose of QUE treated transgenic sickle Berk mice. We suggest that these effects may be due to a decreased sickle RBC interaction with the vascular bed. Our present data provide a strong basis for the therapeutic application of flavonoids in SCD. Further studies are needed to better understand the mechanism of action in vivo for therapeutic effect in SCD. Disclosures Thangaswamy: AMI Life Sciences Private Ltd: Drug supplied Other. Billett:Selexys Pharmaceuticals: Research Funding.

Roll cells and disclinations in sheared nematic polymers

2001 ◽  
Vol 449 ◽  
pp. 179-200 ◽  
Author(s):  
J. J. FENG ◽  
J. TAO ◽  
L. G. LEAL
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Simple Shear ◽  
Flow Direction ◽  
Flow Regimes ◽  
Flow Conditions ◽  
Break Up ◽  
Nematic Polymers ◽  
Defect Nucleation

We use the Leslie–Ericksen theory to simulate the shear flow of tumbling nematic polymers. The objectives are to explore the onset and evolution of the roll-cell instability and to uncover the flow scenario leading to the nucleation of disclinations. With increasing shear rate, four flow regimes are observed: stable simple shear, steady roll cells, oscillating roll cells and irregular patterns with disclinations. In the last regime, roll cells break up into an irregular and uctuating pattern of eddies. The director is swept into the flow direction in formations called ‘ridges’, which under favourable flow conditions split to form pairs of ± 1 disclinations with non-singular cores. The four regimes are generally consistent with experimental observations, but the mechanism for defect nucleation remains to be verified by more detailed measurements.

Ultrasonic Effect on Fabrication of Intercalated MgAl-LDH/PVA Nanocomposites via Exfoliation-Adsorption Route

2017 ◽  
Vol 727 ◽  
pp. 532-536
Author(s):  
Bao Guang Li ◽  
Yong Zi Xu ◽  
Lu Bai ◽  
Huan Dai ◽  
Cai Cai Xie ◽  
...  
Keyword(s):  
Shear Rate ◽  
Double Layer ◽  
Layered Double Hydroxides ◽  
Ultrasonic Treatment ◽  
Flow Direction ◽  
Hybrid Structure ◽  
High Shear ◽  
Ultrasonic Effect ◽  
Double Hydroxides

Glycine intercalated Mg/Al-layered double hydroxides (LDH-G)/PVA nanocomposites were prepared via exfoliation-adsorption route based on exfoliation of LDH-G in formamide. The effect of ultrasonic treatment on the fabrication of LDH-G/PVA nanocomposites was investigated. The results of XRD suggest that chains of PVA with double layer arrange into the galleries of restacking LDH platelets with the formation of intercalated-type nanocomposite. Experiments present that ultrasonic treatment on the colloid of LDH-G/PVA increases the amount of platelet which forms the intercalated phase, and improves the regularity of LDH-G arrays in the c direction. It is demonstrated the exfoliated LDH platelets orient in its normal paralleling the flow direction at the high shear rate induced by ultrasound. Simultaneously, under the enhanced temperature caused by long term of ultrasonic treatment, PVA chains extend more and the interaction between PVA chains and LDH layers is reinforced. A model was proposed for various stages of LDH platelets and PVA chains in their mixed colloid during ultrasonic treatment which describes the fabrication of improved hybrid structure.

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