Shear-thickening Flow Behavior Research Articles

Effect of surface stretching on convective instabilities of Kármán flow of non-Newtonian Carreau fluid

Linear convective instability analysis of non-Newtonian fluids has immense practical applications in the field of aerodynamics and engineering mechanics. The paper deals with linear convective instability analysis of laminar Kármán swirling flow of a non-Newtonian Carreau fluid over a radially stretchable rotating disk of infinite radius when the Coriolis force is significant in the boundary layer. In this paper, the velocity profiles for both shear-thinning and shear-thickening fluids the above-mentioned flow of Carreau model have been determined under stretch boundary condition. By using the Chebyshev collocation method, a study of convective instability has been carried out in order to perform a stability analysis of the flow and determine the neutral stability curves. The stability curves reveal that the bottom disk’s surface stretching has a globally stabilizing effect on the fluid exhibiting shear-thinning flow behaviour and a globally destabilizing effect on shear-thickening flow behaviour. To verify the above physical facts, the flow has been subjected to an energy analysis at the same time.

Shear-induced aggregation of amyloid β (1–40) in a parallel plate geometry

Protein aggregation is induced by various environmental or external factors and associated with various neurodegenerative diseases. Among various external factors, shear stress is inevitable for both in vivo and in vitro applications of proteins. In this study, Aβ (1–40) peptide, a derivative of the amyloid precursor protein, was subjected to constant (300, 500, 700 s−1) and varying (ramp) shear in a parallel plate geometry to explore the implications of shear in terms of macro (viscosity) and micro (secondary structure, morphology) characteristics. Aβ (1–40) solution followed a shear thickening flow behaviour with performance index value ‘n’ of 2.12. The fibrillation process resulting from the shear force was evaluated in terms of dissipation energy, which was found to exceed the free energy of unfolding. This resulted in the formation of β-sheet rich structures, which were confirmed by CD and FTIR analyses and enhanced Th-T fluorescence. The apparent rate of aggregation () was found to increase with the shear rate, and inversely related to the solution viscosity. The maximum value was 0.21 ± 0.3 min−1 at 700 s−1. The molecular weights of aggregates were determined using gel filtration, which were proportionally related to the solution viscosity. The average molecular weights were estimated to be 70, 62 and 52 KDa for samples sheared at 300, 500 and 700 s−1, respectively. The present study has deciphered the interplay of viscosity, a fluid property, with the aggregation process and its corresponding change in the secondary structures of the peptide. These findings provide useful insights for understanding various proteopathies under shear force. Communicated by Ramaswamy H. Sarma

On the appearance of vorticity and gradient shear bands in wormlike micellar solutions of different CPCl/salt systems

Wormlike micellar salt/surfactant solutions (X-salicylate, cetylpyridinium chloride) are studied with respect to the applied shear stress, concentration, temperature, and composition of the counterions (X = lithium, sodium, potassium, magnesium, and calcium) of the salicylate salt solute to determine vorticity and gradient shear bands. A combination of rheological measurements, laser technique, video analysis, and rheo-small-angle neutron scattering allow for a detailed exploration of number and types of shear bands. Typical flow curves of the solutions show Newtonian, shear-thinning, and shear-thickening flow behavior. In the shear-thickening regime, the solutions show vorticity and gradient shear bands simultaneously, in which vorticity shear bands dominate the visual effect, while gradient shear bands always coexist and predominate the rheological response. It is shown that gradient shear bands change their phases (turbid, clear) with the same frequency as the shear rate oscillates, whereas vorticity shear bands change their phases with half the frequency of the shear rate. Furthermore, we show that with increasing molecular mass of the counterions the number of gradient shear bands increases, while the number of vorticity shear bands remains constant. The variation of temperature, shear stress, concentration, and counterions results in a predictable change in the rheological behavior and therefore allows adjustment of the number of vorticity shear bands in the shear band regime.

Cloisite-g-Methacrylic Acid Copolymer Nanocomposites by Graft from Method for Leather Processing

A series of novel facile water dispersible cloisite-g-methacrylic acid copolymers were prepared by graft from method. These graft copolymers were applied on goat skin before and after neutralization processes to produce lightweight, soft, grain tight, and water vapor permeable leather. All the graft copolymers and polymethacrylic acid (PMA) were thoroughly characterized by spectroscopic methods and thermal property changes. The intercalated cloisite-g-methacrylic acid copolymer nanocomposites exhibit a decreasing trend in viscosities with increase in the weight percentage of cloisite. The cloisite-g-methacrylic acid (C-g-MA) copolymers exhibit better thermal stability. All the nanocomposites showed a shear-thickening flow behavior. The stress–strain measurements of leather treated with nanocomposite samples reveal an increase in modulus property with the increase in cloisite content. The low weight percentage graft copolymers nanocomposite treated leathers are lightweight, have better smoothness, and show...

Rheo-SANS Studies on Shear-Thickening/Thinning in Aqueous Rodlike Micellar Solutions

Shear-induced thickening/thinning phenomena of aqueous rodlike micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and micellar structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems.

Integration approach of the Couette inverse problem of powder type self-compacting concrete in a wide-gap concentric cylinder rheometer: Part II. Influence of mineral additions and chemical admixtures on the shear thickening flow behaviour

The influence of mineral additions and chemical admixtures on the shear thickening flow behaviour of powder type self-compacting concrete (SCC) is studied by means of a wide-gap concentric cylinder rheometer. The Couette inverse problem is treated by means of the integration method in order to derive the flow curve τ(γ̇) from the torque measurements. According to the experimental results, the shear thickening effect is found to be strongly influenced by the addition of the chemical admixture (a polycarboxylate ether based superplasticizer), whereas mineral additions were found to modify the intensity of shear thickening. The limestone, quartzite and fly ash addition used in this research project, respectively increase, unalter and decrease the shear thickening intensity. The powder volume and the available amount of free water proved to have a major impact on the viscosity of the powder type SCC mixes. Increasing the powder volume or decreasing the amount of free water results in an increased viscosity of the SCC mix.

Characterization of TiO2 nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO2 deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO2 nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( $$ \dot \gamma $$ = 10–250 s−1). The influence of these parameters on the quality of TiO2 films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO2 nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s−1). For the suspension with 1 wt.% TiO2 containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕm) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕm = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO2 deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.

Transient shear flow properties of carbon fiber-filled liquid crystalline polymer

Unsteady flow of filled polymer systems can cause some difficulties in their processing, such as injection or extrusion molding, in which flow in the molten state is involved. In order to determine the optimum conditions and thus improve the performance of the end products, it is necessary to understand the transient/unsteady flow behavior of these systems. In a previous work, we found remarkable non-Newtonian properties and shear thickening flow behavior of liquid crystalline polymers (LCP) and their filled systems. This article deals with the dependence of transient flow properties, including shear thickening, of pure and carbon fiber-filled LCP upon the shear rate and shear strain history; the effect of the filler content is also discussed. The results indicate that the abnormal flow behavior of the tested materials may be caused by gradual disintegration of the domain structure formed in LCP (materials exhibit apparent yield stress) and then continual orientation of molecules under shear flow. The shear thickening behavior of the materials seems to disappear with increasing fiber content. This behavior suggests that it is necessary to measure the flow properties under a sufficient ramp point delay time and equilibration time in order to obtain reliable data under stable conditions. POLYM. COMPOS., 26:470–476, 2005. © 2005 Society of Plastics Engineers.

Power Law Fluid Flow Through Beds of Spheres at Intermediate Reynolds Numbers: Pressure in Fixed and Distended Beds

Extensive numerical predictions of friction, pressure and total drag coefficients for the steady incompressible flow of power law liquids through assemblages of spherical particles are presented in this paper. The governing equations (continuity and momentum) have been solved numerically for the unknown pressure and velocity components which, in turn, have been used to infer the values of the derived variables like vorticity, stream function, pressure and frictional components of the overall drag coefficient. The inter-particle hydrodynamic interactions have been mimicked by the two commonly used concentric spherein-sphere cell models. The numerical results presented herein span the following ranges of kinematic and physical conditions: power law index, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, thereby including both shear-thinning and shear-thickening flow behaviour; the particle Reynolds number, 1–500; and bed voidages of 0.4, 0.5 and 0.6, thereby covering packed and distended bed conditions. The accuracy of the numerical solution procedure has been validated by carrying out extensive comparisons with the previously available analytical and scant numerical results, mainly limited to the creeping flow conditions. The utility of such a simple approach is demonstrated by presenting detailed comparisons with the experimental results available in the literature.

Dilatant Behavior of Systems with the Thixotropic Agent Aerosil 380 in the Epoxy Resin Araldite GY260

Abstract Model suspension with Aerosil 380 in epoxy resin Araldite GY260 and Aerosil 380 in silicone oil M20000 are compared. The systems with 7.5%, 10% and 12.5% Aerosil 380 in Araldite GY260 show shear thickening flow behavior. A shear induced hydrodynamic force effects at the onset of shear thickening a disorder of the well ordered movement of the Areosil particles in layers. The Areosil particles build-up a pseudo-mixture that lead to a sudden development of a three dimensional structure, i.e. to viscosity incerease. One can assume that the shear thickening can be explained with an order-to-disorder transition. The viscosity increase of the shear thickening region is limited – It can reach topmost the plastic viscosity curve that has to be expected from the beginning. The dilatant system begins in the third straight line section to coincide the viscosity curve of the expected plastic system for the subsequent thixotropic agent concentration.

Granule size and rheological behavior of heated tapioca starch dispersions

Rheological behavior of starch dispersions is strongly influenced by the granules. From granule size data of 2.6% tapioca starch dispersions (STDs) isothermally heated in the range 61°C–74°C obtained by laser diffraction, the maximum average granule size was found to be 3.7×the raw starch granule mean diameter. Compared to corn and cowpea starches, heated tapioca starch granules had a higher initial maximum diameter that was less dependent on the heating temperature, and the ratio of the heated to unheated starch granule diameter ratio contributed to a higher increase of notional volume fractions (cQ) of the tapioca STDs. Shear-thickening flow behavior was observed in STDs heated at 61°C for 1, 5 and 15min, and shear-thinning in all other dispersions. The Casson and Quemada models described well the apparent viscosity versus shear rate data of the STDs at different notional volume fractions. The power law consistency index increased exponentially with granule size reflecting increase in dispersion viscosity. The relative viscosity vs cQ data of the STDs followed Quemada's structural model. A modified Cox–Merz rule described the relationship between complex viscosity and apparent viscosity of a 4% dispersion.

Explanations for the cause of shear thickening in concentrated colloidal suspensions

In contrast to recent publications suggesting that particle cluster formation alone can play an important role in the shear thickening flow behavior of concentrated colloidal suspensions, we believe that there is little if any substantive evidence to prove it. To support this view, we use data from various studies, including data from studies concluding that layered flow is not involved. One reason for the confusion seems to center around the inability of various light-scattering and neutron-scattering techniques to show particle layering before shear thickening when the layers are not well defined. In this regard, one should understand that layered flow can occur without rigorous ordering of particles within the layers, and as the flowing suspension approaches the point of instability, the hydrodynamic forces driving for the instability will jostle the particles within the layers sufficiently to make it even harder to see the layering and any ordering, if it exists, within the layers. Having these views, we argue that the process described by Hoffman (1972, 1974) for shear thickening is still applicable with refinements. The major refinement is the idea that, after the hydrodynamic forces cause the instability which breaks up the layered flow, particle jamming probably involves cluster formation both with and without particle contact. Particle roughness and angularity will facilitate the contact. Finally, we agree with various authors who argue that the best chance of finding shear thickening in concentrated colloidal suspensions without layer formation lies in Brownian hard-sphere suspensions, but the evidence given for it so far is not definitive.