scholarly journals Imaging the Microscopic Structure of Shear Thinning and Thickening Colloidal Suspensions

Science ◽  
2011 ◽  
Vol 333 (6047) ◽  
pp. 1276-1279 ◽  
Author(s):  
Xiang Cheng ◽  
Jonathan H. McCoy ◽  
Jacob N. Israelachvili ◽  
Itai Cohen
Keyword(s):  
Hydrodynamic Lubrication ◽  
Flow Behavior ◽  
Shear Thickening ◽  
Colloidal Suspensions ◽  
Shear Thinning ◽  
Particle Dynamics ◽  
Industrial Processes ◽  
Force Measurements ◽  
Relative Contribution ◽  
Newtonian Behavior

The viscosity of colloidal suspensions varies with shear rate, an important effect encountered in many natural and industrial processes. Although this non-Newtonian behavior is believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics are difficult to measure. By combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension’s structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by hydrodynamic lubrication forces. This combination of techniques illustrates an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids.

The Low-Pressure Rheology of Ultra-Thin Lubricant Films and Its Influence on Sliding Contact

1994 ◽  
Vol 116 (1) ◽  
pp. 119-126 ◽  
Author(s):  
J. L. Streator ◽  
J. P. Gerhardstein ◽  
C. B. McCollum
Keyword(s):  
Shear Stress ◽  
Hydrodynamic Lubrication ◽  
Force Measurements ◽  
Disk Interface ◽  
Shear Rates ◽  
Lubricant Films ◽  
Asperity Contacts ◽  
Lubricated Contact ◽  
Mixed Lubrication Regime ◽  
Newtonian Behavior

Lubricant rheology governs the friction in any lubricated contact. In hydrodynamic lubrication, the genesis of friction is well-understood. However, when asperity contacts occur, the situation becomes more complex. In this “mixed” lubrication regime, it is known that lubricants can deviate dramatically from Newtonian behavior, but the source of this effect has not been identified. In particular, the question arises as to whether the non-Newtonian behavior of the lubricant is due to the extreme thinness of the film or to the very large shear rates to which it is subjected. In the current work, we analyze friction force measurements in the magnetic slider/disk interface to help resolve this question. Because of its precision geometry, the slider/disk interface is ideal for such an investigation. Results of the analysis indicate (1) the lubricant retains its bulk viscosity in films as thin as 11–12 molecular diameters; (2) the rheological state of the lubricant is determined by a parameter we introduce here as the “Newtonian” shear stress, and (3) the rheology of the lubricant at high Newtonian shear stress may indicate a newly discovered property of liquids.

scholarly journals Analysis of Arrhenius Kinetics on Multiphase Flow between a Pair of Rotating Circular Plates

2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
M. B. Arain ◽  
M. M. Bhatti ◽  
A. Zeeshan ◽  
Tareq Saeed ◽  
Aatef Hobiny
Keyword(s):  
Flow Behavior ◽  
Fluid Velocity ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Three Dimensions ◽  
Fluid Viscosity ◽  
Circular Plates ◽  
Carreau Fluid ◽  
Moving Plate ◽  
The Impact

In this study, we aim to deal with the flow behavior betwixt a pair of rotating circular plates filled with Carreau fluid under the suspension of nanoparticles and motile gyrotactic microorganisms in the presence of generalized magnetic Reynolds number. The activation energy is also contemplated with the nanoparticle concentration equation. The appropriate similarity transformations are used to formulate the proposed mathematical modeling in the three dimensions. The outcomes of the torque on both plates, i.e., the fix and the moving plate, are also contemplated. A well-known differential transform method (DTM) with a combination of Padé approximation will be implemented to get solutions to the coupled nonlinear ordinary differential equations (ODEs). The impact of different nondimensional physical aspects on velocity profile, temperature, concentration, and motile gyrotactic microorganism functions is discussed. The shear-thinning fluid viscosity decreases with shear strain due to its high velocity compared to the Newtonian and shear-thickening case. The impact of Carreau fluid velocity for shear-thinning n < 1 , Newtonian case n = 0 , and shear-thickening n > 1 cases on axial velocity distribution f ′ λ has been discussed in tabular form and graphical figures. For the validation of the current methodology, a comparison is made between DTM-Padé and the numerical shooting scheme.

Rheological effects on the levelling dynamics of thin fluid films

2015 ◽  
Vol 25 (8) ◽  
pp. 1850-1867 ◽  
Author(s):  
Gulraiz Ahmed ◽  
Mathieu Sellier ◽  
Yeaw Chu Lee ◽  
Mark Jermy ◽  
Michael Taylor
Keyword(s):  
Flow Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Lubrication Approximation ◽  
Fluid Films ◽  
Flow Behavior Index ◽  
Shear Thickening Fluid ◽  
Content Type ◽  
Shear Thinning Fluid ◽  
Behavior Index

Purpose – The purpose of this paper is to investigate numerically the effect of rheology on the leveling of thin fluid films on horizontal solid substrates. Design/methodology/approach – A mathematical model based on the lubrication approximation which defines non-Newtonian rheology using a Power-law model is presented. The rheology is described by two parameters: the consistency factor and the flow behavior index. The resulting highly non-linear coupled set of equations is discretized using Finite-Difference and the resulting algebraic system is solved via an efficient Multigrid algorithm. Findings – Importantly, the non-dimensionalization process leads to a pair of Partial Differential Equations which depends on one parameter only, the flow behavior index. The authors show that the consistency factor only affects the time scale of the leveling process, hence stretching or contracting the time line. Results for the leveling of sinusoidal perturbations of the fluid film highlights important differences between the leveling of shear-thinning and shear-thickening fluids. In a normalized time frame, the onset of leveling occurs earlier for the shear-thinning fluid than for the shear-thickening one. However, the dimensionless leveling rate is higher for the shear-thickening fluid than the shear-thinning one. This results in a “threshold thickness” which delimits two regimes: the shear-thinning fluid levels to a thickness above this threshold faster than the shear-thickening fluid but the opposite is true for a film thickness below this threshold. An important aspect of this study is the verification of the numerical implementation using the Method of Manufactured Solutions (MMS), a first in the context of thin film studies. The paper also highlights differences between the leveling of two-dimensional and three-dimensional thickness perturbations. Originality/value – The study of the leveling of disturbances at the free surface of a liquid film using a Power-law rheological model does not appear to have been covered in the literature. Also, the paper uses the MMS to test the validity of the implementation. This appears to be the first time it has been used in the context of the lubrication approximation. Finally, unlike most prior studies, the work does away with the planar assumption.

scholarly journals Air bubbles play a role in shear thinning of non-colloidal suspensions

2021 ◽  
Vol 33 (1) ◽  
pp. 011702
Author(s):  
Yuan Lin ◽  
Ying Wang ◽  
Zixin Weng ◽  
Dingyi Pan ◽  
Jiawang Chen
Keyword(s):  
Colloidal Suspensions ◽  
Shear Thinning ◽  
Air Bubbles

scholarly journals Shear thickening behavior in dense repulsive and attractive suspensions of hard spheres

Soft Matter ◽  
2021 ◽  
Author(s):  
Vikram Rathee ◽  
Alessandro Monti ◽  
Marco Edoardo Rosti ◽  
Amy Q Shen
Keyword(s):  
Flow Curve ◽  
Hard Spheres ◽  
Shear Thickening ◽  
Colloidal Suspensions ◽  
Thickening Behavior ◽  
The Stability

Shear thickening in stable dense colloidal suspensions is a reversible phenomenon and no hysteresis is observed in the flow curve measurements. However, a reduction in the stability of colloids promotes...

The Effect of Nanoparticle Functionalization on Lubrication Performance of Nanofluids Dispersing Silica Nanoparticles in an Ionic Liquid

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Cengiz Yegin ◽  
Wei Lu ◽  
Bassem Kheireddin ◽  
Ming Zhang ◽  
Peng Li ◽  
...  
Keyword(s):  
Silica Nanoparticles ◽  
Coefficient Of Friction ◽  
Shear Thinning ◽  
Antiwear Additives ◽  
Functionalized Silica ◽  
Low Concentrations ◽  
Lubrication Performance ◽  
The Coefficient Of Friction ◽  
High Concentrations ◽  
Newtonian Behavior

Recently, ionic liquids (ILs) have received an increasing attention as lubricants owing to their intriguing properties such as tunable viscosity, high thermal stability, low emissions, nonflammability, and corrosion resistance. In this work, we investigate how the incorporation of octadecyltrichlorosilane (OTS) functionalized silica nanoparticles (NPs) in 1-butyl-3-methylimidazolium (trifluoromethysulfony)imide influences the tribological properties and rheological properties of IL under boundary lubrication and elastohydrodynamic conditions, respectively. It was found that the coefficient of friction was depended on the concentration of NPs in IL with a concave upward functional trend with a minimum at 0.05 wt.% for bare silica NPs and at 0.10 wt.% for OTS-functionalized silica NPs. For steel–steel sliding contact, the presence of functionalized NPs in IL at the optimum concentration decreased the coefficient of friction by 37% compared to IL and 17% compared to IL with bare silica NPs. While IL with bare NPs demonstrated a shear thinning behavior for all concentrations, IL with functionalized NPs showed a Newtonian behavior at low concentrations and shear thinning behavior at high concentrations. Overall, this study provides new insights into the antifriction and antiwear additives for lubrication systems involving ILs.

Stability of Shear-Thickening Liquids Between Rotating Cylinders

2010 ◽  
Author(s):  
Nariman Ashrafi ◽  
Habib Karimi Haghighi
Keyword(s):  
Couette Flow ◽  
Dynamical Behavior ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Taylor Vortex ◽  
Shear Dependent Viscosity ◽  
Shear Thinning Fluids ◽  
Shear Thickening Fluids ◽  
The Stability ◽  
Dependent Viscosity

The effects of nonlinearities on the stability are explored for shear thickening fluids in the narrow-gap limit of the Taylor-Couette flow. It is assumed that shear-thickening fluids behave exactly as opposite of shear thinning ones. A dynamical system is obtained from the conservation of mass and momentum equations which include nonlinear terms in velocity components due to the shear-dependent viscosity. It is found that the critical Taylor number, corresponding to the loss of stability of Couette flow becomes higher as the shear-thickening effects increases. Similar to the shear thinning case, the Taylor vortex structure emerges in the shear thickening flow, however they quickly disappear thus bringing the flow back to the purely azimuthal flow. Naturally, one expects shear thickening fluids to result in inverse dynamical behavior of shear thinning fluids. This study proves that this is not the case for every point on the bifurcation diagram.

scholarly journals Structural Characterization andIn VitroAntioxidant Activity of Kojic Dipalmitate Loaded W/O/W Multiple Emulsions Intended for Skin Disorders

2015 ◽  
Vol 2015 ◽  
pp. 1-8 ◽  
Author(s):  
Maíra Lima Gonçalez ◽  
Diana Gleide Marcussi ◽  
Giovana Maria Fioramonti Calixto ◽  
Marcos Antonio Corrêa ◽  
Marlus Chorilli
Keyword(s):  
Antioxidant Activity ◽  
Safety Profile ◽  
Flow Behavior ◽  
Microscopic Analysis ◽  
Skin Disorders ◽  
Activity Assay ◽  
Multiple Emulsions ◽  
Lipophilic Antioxidant ◽  
Newtonian Behavior

Multiple emulsions (MEs) are intensively being studied for drug delivery due to their ability to load and increase the bioavailability of active lipophilic antioxidant, such as kojic dipalmitate (KDP). The aim of this study was to structurally characterize developed MEs by determining the average droplet size (Dnm) and zeta potential (ZP), performing macroscopic and microscopic analysis and analyzing their rheological behavior andin vitrobioadhesion. Furthermore, thein vitrosafety profile and antioxidant activity of KDP-loaded MEs were evaluated. The developed MEs showed a Dnm of approximately 1 micrometer and a ZP of −13 mV, and no change was observed in Dnm or ZP of the system with the addition of KDP. KDP-unloaded MEs exhibited ‘‘shear thinning’’ flow behavior whereas KDP-loaded MEs exhibited Newtonian behavior, which are both characteristic of antithixotropic materials. MEs have bioadhesion properties that were not influenced by the incorporation of KDP. The results showed that the incorporation of KDP into MEs improved the safety profile of the drug. Thein vitroantioxidant activity assay suggested that MEs presented a higher capacity for maintaining the antioxidant activity of KDP. ME-based systems may be a promising platform for the topical application of KDP in the treatment of skin disorders.

scholarly journals The Effect of Rheology of Viscoelastic Polymer on Pressure Transient Response in Near-Wellbore Regions

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Jia Zhang ◽  
Shiqing Cheng ◽  
Jie Zhan ◽  
Qi Han
Keyword(s):  
Shear Thickening ◽  
Shear Thinning ◽  
Polymer Flooding ◽  
High Shear ◽  
Pressure Data ◽  
Transient Pressure ◽  
Pressure Derivative ◽  
Shear Rates ◽  
Viscoelastic Polymer ◽  
Thickening Behavior

Viscoelastic polymer solution shows shear thinning behavior at low shear rates and shear thickening behavior at high shear rates in reservoirs. However, models that ignored shear thickening behavior were commonly employed to interpret transient pressure data derived from tested wells in viscoelastic polymer flooding systems; although, viscoelastic polymer solutions show shear thickening behavior in the near-wellbore region due to high shear rate. To better characterize the oilfield with pressure transient analysis in viscoelastic polymer flooding systems, we developed a numerical model that takes into account both shear thinning behavior and shear thickening behavior. A finite volume method was employed to discretize partially differential flow equations in a hybrid grid system including PEBI mesh and Cartesian grid, and the Newton-Raphson method was used to solve the fully implicit nonlinear system. To illustrate the significance of our model, we compared our model with a model that ignores the shear thickening behavior by graphing their solutions on log-log plots. In the flow regime of near-wellbore damage, the pressure derivative computed by our model is distinctly larger than that computed by the model ignoring shear thickening behavior. Furthermore, the effect of shear thickening behavior on pressure derivative differs from that of near-wellbore damage. We then investigated the influence of shear thickening behavior on pressure derivative with different polymer injection rates, injection rates, and permeabilities. The results can provide a benchmark to better estimate near-wellbore damage in viscoelastic polymer flooding systems. Besides, we demonstrated the applicability and accuracy of our model by interpreting transient pressure data from a field case in an oilfield with viscoelastic polymer flooding treatments.

The Granular Lubricated Journal Bearing: Evidence of Lift Formation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Venkata K. Jasti ◽  
Martin C. Marinack ◽  
Deepak Patil ◽  
C. Fred Higgs
Keyword(s):  
Carrying Capacity ◽  
Granular Flow ◽  
High Speed ◽  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Flow Behavior ◽  
Extreme Environments ◽  
Granular Flows ◽  
Load Carrying Capacity ◽  
Load Carrying

This work demonstrates that granular flows (i.e., macroscale, noncohesive spheres) entrained into an eccentrically converging gap can indeed actually exhibit lubrication behavior as prior models postulated. The physics of hydrodynamic lubrication is quite well understood and liquid lubricants perform well for conventional applications. Unfortunately, in certain cases such as high-speed and high-temperature environments, liquid lubricants break down making it impossible to establish a stable liquid film. Therefore, it has been previously proposed that granular media in sliding convergent interfaces can generate load carrying capacity, and thus, granular flow lubrication. It is a possible alternative lubrication mechanism that researchers have been exploring for extreme environments, or wheel-regolith traction, or for elucidating the spreadability of additive manufacturing materials. While the load carrying capacity of granular flows has been previously demonstrated, this work attempts to more directly uncover the hydrodynamic-like granular flow behavior in an experimental journal bearing configuration. An enlarged granular lubricated journal bearing (GLJB) setup has been developed and demonstrated. The setup was made transparent in order to visualize and video capture the granular collision activity at high resolution. In addition, a computational image processing program has been developed to process the resulting images and to noninvasively track the “lift” generated by granular flow during the journal bearing operation. The results of the lift caused by granular flow as a function of journal rotation rate are presented as well.

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