scholarly journals The Chain Distribution Tensor: Linking Nonlinear Rheology and Chain Anisotropy in Transient Polymers

Polymers ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 848 ◽  
Author(s):  
Shankar Lalitha Sridhar ◽  
Franck Vernerey
Keyword(s):  
Shear Rate ◽  
Polymer Networks ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Underlying Mechanism ◽  
Weissenberg Number ◽  
Critical Shear Rate ◽  
Nonlinear Rheology ◽  
Non Gaussian ◽  
Chain Force

Transient polymer networks are ubiquitous in natural and engineered materials and contain cross-links that can reversibly break and re-form. The dynamic nature of these bonds allows for interesting mechanical behavior, some of which include nonlinear rheological phenomena such as shear thickening and shear thinning. Specifically, physically cross-linked networks with reversible bonds are typically observed to have viscosities that depend nonlinearly on shear rate and can be characterized by three flow regimes. In slow shear, they behave like Newtonian fluids with a constant viscosity. With further increase in shear rate, the viscosity increases nonlinearly to subsequently reach a maximum value at the critical shear rate. At this point, network fracture occurs followed by a reduction in viscosity (shear-thinning) with a further increase in shear rate. The underlying mechanism of shear thickening in this process is still unclear with debates between a conversion of intra-chain to inter-chain cross-linking and nonlinear chain stretch under high tension. In this paper, we provide a new framework to describe the nonlinear rheology of transient polymer networks with the so-called chain distribution tensor using recent advances from the transient network theory. This tensor contains quantitatively and statistical information of the chain alignment and possible anisotropy that affect network behavior and mechanics. We investigate shear thickening as a primary result of non-Gaussian chain behavior and derive a relationship for the nonlinear viscosity in terms of the non-dimensional Weissenberg number. We further address the criterion for network fracture at the critical shear rate by introducing a critical chain force when bond dissociation is suddenly accelerated. Finally, we discuss the role of cross-linker density on viscosity using a “sticky” reptation mechanism in the context of previous studies on metallo-supramolecular networks with reversible cross-linkers.

On Shear Thinning in Dilute Polymer Solutions

1989 ◽  
Vol 177 ◽  
Author(s):  
Yitzhak Rabin ◽  
H. C. Öttinger ◽  
K. Kawasaki
Keyword(s):  
Shear Rate ◽  
Polymer Solutions ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Weissenberg Number ◽  
Dilute Polymer Solutions

ABSTRACTWhile recent remrmalization group studies predict shear thickening in the limit of large Weissenberg numbers, scaling theories predict shear thinning. The ocntroversy is related to the question whether the Weissenberg number or the shear rate should be kept fixed when taking the limit of infinitely long polymers.

scholarly journals Critical Shear Rate of Polymer-Enhanced Hydraulic Fluids

Lubricants ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 102
Author(s):  
Pawan Panwar ◽  
Paul Michael ◽  
Mark Devlin ◽  
Ashlie Martini
Keyword(s):  
Molecular Weight ◽  
Shear Rate ◽  
Shear Thinning ◽  
Hydraulic Systems ◽  
Newtonian Viscosity ◽  
Critical Shear Rate ◽  
Base Oil ◽  
Hydraulic Fluids ◽  
Theoretical Predictions ◽  
Dynamics Simulations

Many application-relevant fluids exhibit shear thinning, where viscosity decreases with shear rate above some critical shear rate. For hydraulic fluids formulated with polymeric additives, the critical shear rate is a function of the molecular weight and concentration of the polymers. Here we present a model for predicting the critical shear rate and Newtonian viscosity of fluids, with the goal of identifying a fluid that shear thins in a specific range relevant to hydraulic pumps. The model is applied to predict the properties of fluids comprising polyisobutene polymer and polyalphaolefin base oil. The theoretical predictions are validated by comparison to viscosities obtained from experimental measurements and molecular dynamics simulations across many decades of shear rates. Results demonstrate that the molecular weight of the polymer plays a key role in determining the critical shear rate, whereas the concentration of polymer primarily affects the Newtonian viscosity. The simulations are further used to show the molecular origins of shear thinning and critical shear rate. The atomistic simulations and simple model developed in this work can ultimately be used to formulate polymer-enhanced fluids with ideal shear thinning profiles that maximize the efficiency of hydraulic systems.

Cold start analysis of an engine coolant-MWCNT nanofluid: Synthesis and viscosity behavior under shear stress

2021 ◽  
pp. 095440702110192
Author(s):  
Luiz U R Sica ◽  
Edwin M C Contreras ◽  
Enio P Bandarra Filho ◽  
José A R Parise
Keyword(s):  
Thermal Conductivity ◽  
Shear Stress ◽  
Shear Rate ◽  
Internal Combustion Engines ◽  
Shear Thickening ◽  
Cold Start ◽  
Shear Thinning ◽  
Pollutant Emissions ◽  
Flow Index ◽  
Engine Coolant

During cold start of internal combustion engines, coolant temperature, and thermal conductivity are key parameters in the heat transfer processes that ultimately affect pollutant emissions and engine performance. Hereupon the use of coolants with suspended nanoparticles, to enhance thermal conductivity, emerged as a promising technology. However, for Newtonian materials, viscosity also increases with nanoparticle concentration. To overcome increased pumping power, the use of non-Newtonian nanofluids makes such application potentially feasible, specifically for shear-thinning materials, in which a higher shear rate leads to reducing shear viscosity due to higher shear stress. Accordingly, a nanofluid, suitable for engine cooling (0.2 wt.% MWCNT-engine coolant/distilled water 30/70 v/v%), was here fabricated and mapped. Shear rate and temperature were varied, with focus on cold start investigation. Shear thinning and shear thickening regions were mapped according to the shear rate levels, for each temperature considered. The nanofluid behaved as shear-thinning material for the entire range of temperatures (−10°C–25°C). Above shear rates of 500 s−1 and flow curves with temperatures below −5°C, a prominent shear thickening behavior was observed. Additionally, the relative apparent viscosity data were compared with four classical models. Regarding the curve fitting parameters of a modified Herschel-Bulkley equation, above 0°C, the apparent yield stress, [Formula: see text], was invariant with temperature. Besides, for the temperature range from 0°C to 20°C, the flow index remained approximately constant. For temperatures above −5°C, infinite-shear-rate viscosity and consistency index presented a linear decrease and a third-degree polynomial-like behavior, respectively.

Steady shear and dynamic strain thickening of halloysite nanotubes and fumed silica shear thickening composite

2018 ◽  
Vol 38 (10) ◽  
pp. 915-923
Author(s):  
Pavni Passey ◽  
Mansi Singh ◽  
Sanjeev K. Verma ◽  
Debarati Bhattacharya ◽  
Rajeev Mehta
Keyword(s):  
Shear Rate ◽  
Fumed Silica ◽  
Shear Thickening ◽  
Halloysite Nanotubes ◽  
Spherical Particles ◽  
Dynamic Strain ◽  
Critical Shear Rate ◽  
Shear Thickening Fluids ◽  
Protective Fabrics ◽  
Critical Viscosity

Abstract Developing the shear thickening fluids (STF) which can be used for soft body armours requires an in depth study of various parameters related to its constituents so that a high critical viscosity along with high critical shear rate can be obtained. Shape of the constituting particles is one such important parameter. Elongated and nanosize particles provide high critical viscosity to the fluid, whereas spherical particles show high critical shear rates. STF were prepared using halloysite (Hal) nanotubes of different concentrations with fumed silica (spheres) and their rheological properties were studied. A better non-flocculated structure was obtained at 1% Hal in 20% fumed silica composition, exhibiting a critical viscosity of 25 Pas at a critical shear rate 160 s−1 as compared to that of only spherical particle STF (10 Pas and 200 s−1). The oscillatory tests revealed that this composition, with a better consistent reproducible behaviour and better stability than the STF without Hal, would be suitable as a high impact resistant material. Gel formation does not take place, rather the fluid behaves like a dispersed sol, making it a better choice for using with protective fabrics. The rheology was studied at different temperatures ranging from 0°C to 55°C.

Tuning the Rheology of Nano-Sized Silica Suspensions with Silicon Nitride Particles

2019 ◽  
Vol 56 ◽  
pp. 63-70 ◽  
Author(s):  
Selim Gürgen
Keyword(s):  
Silicon Nitride ◽  
Shear Rate ◽  
Shear Thickening ◽  
Critical Shear Rate ◽  
Rheological Measurements ◽  
Additive Particles ◽  
Thickening Behavior ◽  
Silica Suspensions ◽  
Nanosized Silica

In this paper, a non-Newtonian fluid was fabricated dispersing nanosized silica particles in a polyethylene glycol medium. The rheology of the suspension was investigated in a stress-controlled rheometer under increasing shear rate. Based on the rheological measurements, the suspension exhibited shear thickening behavior which gives a drastic viscosity grow with the increase in the shear rate. In order to investigate the role of the micro-sized additive particles on the rheology of silica based suspension, silicon nitride particles were included in the suspension with three different concentrations. The results were discussed in terms of important parameters for the shear thickening mechanism such as critical shear rate, peak viscosity, thickening ratio and initial viscosity. According to the results, shear thickening behavior can be controlled altering the amount of silicon nitride particles in the suspension.

scholarly journals Investigation of penetration into woven fabric specimens impregnated with shear thickening fluid

2018 ◽  
Vol 25 (1) ◽  
pp. 205-212 ◽  
Author(s):  
Naser Kordani ◽  
Ali Sadough Vanini
Keyword(s):  
Molecular Weight ◽  
Hydrogen Bond ◽  
Shear Rate ◽  
High Molecular Weight ◽  
Particle Surface ◽  
Shear Thickening ◽  
Silica Particles ◽  
Woven Fabric ◽  
Critical Shear Rate ◽  
Shear Thickening Fluid

AbstractIn this paper, the effect of weight fraction of nano silica (hydrophilic fumed silica particles) and molecular mass of polyethylene glycol (PEG) on the rheological properties such as the critical shear rate of fluids has been studied. Dynamic moduli based on strain and the effects of increasing the molecular weight are presented. Constructed samples with high-molecular-weight PEG have higher initial, final and critical viscosities. Also, higher molecular chains in the polymer and preventing the movement of most of these chains against the relative motion of liquid (viscosity) will cause higher viscosity in samples. Critical shear rate is lower in the provided samples with high-molecular-weight PEG. Polymer branches in these suspensions are absorbed by the surface of the particles. Due to OH bonds in the silica particles and also due to the presence of this bond in PEG, creating a hydrogen bond is likely. Such a hydrogen bond between the polymer yarn and the particle surface causes surface absorption of the particles. To show the effect of molecular weight on fibers, woven fabric specimens impregnated with shear thickening fluid (STF) have been examined by penetration and pressure test diagrams have been investigated. In a sample with higher molecular weight, displacement to yield point is higher and residence to penetration does not show much difference.

scholarly journals Continuous phenomenological modeling for the viscosity of shear thickening fluids

2018 ◽  
Vol 8 ◽  
pp. 184798041878655 ◽  
Author(s):  
Minghai Wei ◽  
Li Sun ◽  
Peipei Qi ◽  
Chunguang Chang ◽  
Chunyang Zhu
Keyword(s):  
Shear Rate ◽  
Shear Thickening ◽  
Data Sets ◽  
External Energy ◽  
Critical Shear Rate ◽  
Phenomenological Modeling ◽  
Shear Thickening Fluid ◽  
Shear Thickening Fluids ◽  
Viscosity Modeling ◽  
Independent Experimental Data

In general, shear thickening fluids show a marked increase in viscosity beyond a critical shear rate, which can be attributed to the hydrodynamic clustering effects, where in any external energy acting on a shear thickening fluid is dissipated quickly. However, there is a lack of theoretical modeling to predict the viscosity curve of shear thickening fluids, which changes continuously with the increasing shear rate. In this article, a phenomenological continuous viscosity modeling for a class of shear thickening fluids is proposed. The modeling predicts shear thickening and thinning behaviors that are naturally exhibited by shear thickening fluids for high and high enough values of the shear rate. The result shows that the phenomenological modeling provides a very good fit for several independent experimental data sets. Therefore, the proposed modeling can be used in numerical simulations and theoretical analysis across different engineering fields.

scholarly journals Polymer Optimisation- Shear Thinning or Thickening?

2019 ◽  
Vol 7 (4) ◽  
Author(s):  
Gloria Gyanfi ◽  
Wilberforce Nkrumah Aggrey ◽  
Ernest Ansah Owusu ◽  
Kofi Ohemeng Prempeh
Keyword(s):  
Shear Rate ◽  
Enhanced Oil Recovery ◽  
Oil Recovery ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Injection Rate ◽  
Injection Well ◽  
Polymer Injection ◽  
Well Pattern ◽  
The Impact

With most polymers employed in polymer enhanced oil recovery exhibiting one or both non-Newtonian behaviours that is shear thickening and thinning at different shear rate, it is expedient to analyse the impact of these non-Newtonian behaviours in polymer optimisation. CMG simulation suite was employed to analyse the permeability pinch-out formation with a five (5) spot injection well pattern for a 360days simulation run using a 90days polymer injection well cycling. Shear thinning polymer was found not to be conducive for lower permeable formation as a high percentage of the polymer was retained. NPV was affected by polymer injection rate which controlled polymer optimisation

Influence of Temperature and Shear Rate on Rheological Properties of CTAC/NaSal Aqueous Solution

2019 ◽  
Vol 12 (4) ◽  
pp. 296-311
Author(s):  
Mingjun Pang ◽  
Chengcheng Xie
Keyword(s):  
Shear Rate ◽  
Rheological Properties ◽  
Shear Viscosity ◽  
Chemical Engineering ◽  
Sodium Salicylate ◽  
Shear Thickening ◽  
Shear Thinning ◽  
Power Law Function ◽  
Cetyltrimethyl Ammonium ◽  
Increasing Temperature

Background: It is very important for understanding the turbulence drag-reducing mechanism and for improving product quality in the fields of pharmaceutical and chemical engineering to deeply investigate the rheological properties of surfactants solutions. Methods: The rheological properties of Cationic surfactant (Cetyltrimethyl Ammonium Chloride)/Sodium salicylate were measured and analyzed with the MCR302 rheometer. Results: The present results show that the shear viscosity of CTAC/NaSal solution with the exception of 0.9375mmol·L-1 can show the Newtonian characteristic, the shear-thickening, the shear-thinning and the stable shear properties with changing shear time. The induction time increases with a shear rate as a power law function relation tind=aγb. Conclusion: The shear viscosity of the CTAC/NaSal solution can be divided into three regions with shear rate, and its flow curve conforms to a linear function in the logarithmic coordinate. When the concentration and the shear rate are relatively high, the viscosity curve of the CTAC/NaSal solution appears "platform" at the high temperature. When the shear rate is greater than 90s-1, the shear viscosity only appears shear thinning with increasing temperature.

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