Critical Shear Rate for Gelation in Aqueous Solutions of Associating Polymers under Shear Flows

2018 ◽  
Vol 87 (7) ◽  
pp. 074801
Author(s):  
Fumihiko Tanaka ◽  
Rika Takeda ◽  
Kyoichi Tsurusaki
Keyword(s):  
Shear Rate ◽  
Aqueous Solutions ◽  
Shear Flows ◽  
Critical Shear Rate ◽  
Associating Polymers

Shear degradation resistance of star poly(ethyleneimine) - polyacrylamides during elongational flow

e-Polymers ◽  
2011 ◽  
Vol 11 (1) ◽  
Author(s):  
Ming Duan ◽  
Shenwen Fang ◽  
Liehui Zhang ◽  
Fuxiao Wang ◽  
Peng Zhang ◽  
...  
Keyword(s):  
Shear Rate ◽  
Aqueous Solutions ◽  
Relative Viscosity ◽  
Reduction Rate ◽  
Elongational Flow ◽  
Exponential Dependence ◽  
Distilled Water ◽  
Shear Stability ◽  
Low Viscosity ◽  
Shear Degradation

AbstractAn experimental study of the flow-induced scission behaviour of four star hydrolyzed polyacrylamides (HPMA) with different arms during planar elongational flow in a cross-slot flow cell is described. The results showed that the shear stability of linear HPAM in distilled water was not essentially different from star HPAM. Polymer scission was not observed in either system in a shear rate range from 20,000 to 100,000s-1, which can be attributed to the strong polyelectrolyte behaviour of HPAM in distilled water. However, at the same shear rate, the star HPAMs exhibited superior shear stability in comparison to the linear HPAMs in aqueous solutions containing NaCl (CNaCl=0.2-1.0%wt) and, in particular, the initial reduction rate of relative viscosity (R) decreased with the degree of branching of the HPAMs. In addition, it was found that the R of five HPAMs in NaCl aqueous solutions exhibited an exponential dependence on shear rate, in which the coefficient C1 can be used to quantitatively evaluate shear stability. In star HPAM NaCl aqueous solutions, the increase of R with shear rate is very likely due to the decrease of the hydrodynamic radius (Rh) of these HPAMs, while the increase of R with NaCl concentrations can be attributed to the relatively low viscosity of these polymers at high NaCl concentrations.

Flow Behaviors of High Acyl Gellan Aqueous Solutions as Affected by Temperature, and Calcium and Gellan Concentrations

2008 ◽  
Vol 4 (5) ◽  
Author(s):  
Yiqun Huang ◽  
Pawan Singh Takhar ◽  
Juming Tang ◽  
Barry G Swanson
Keyword(s):  
Shear Rate ◽  
Aqueous Solutions ◽  
Apparent Viscosity ◽  
Flow Resistance ◽  
Effect Of Temperature ◽  
Temperature Changes ◽  
Influence Of Temperature ◽  
Rheological Behaviors ◽  
Low Concentrations ◽  
Influence Of Temperature On

Rheological behaviors of high acyl (HA) gellan are not well understood partially because of its relatively late commercialization compared to low acyl gellan. The objective of this study was to investigate the effect of temperature (5-30 °C), calcium (0, 1 and 10 mM) and gellan concentrations (0.0044-0.1000% w/v) on the flow behaviors of high acyl gellan aqueous solutions using rheological tests. Gellan solutions with 0 or 1 mM added Ca++ exhibited shear thinning behavior at gellan concentrations above 0.0125%. The influence of temperature on apparent viscosity (shear rate, 100 s-1) of gellan solutions can be described with an Arrhenius relationship. The apparent viscosity of gellan solution at low concentrations was more sensitive to temperature changes. The addition of Ca++ led to a decrease in flow resistance for a dilute gellan solution (<0.0125%), but an increased resistance for a relatively concentrated gellan solution (>0.0125%).

scholarly journals Hydrodynamic Shear Effects on Grafted and Non-Grafted Collapsed Polymers

Polymers ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 926 ◽  
Author(s):  
Richard Schwarzl ◽  
Roland Netz
Keyword(s):  
Shear Rate ◽  
Brownian Dynamics ◽  
Tensile Force ◽  
Grafted Polymers ◽  
Critical Shear Rate ◽  
Rate Dependent ◽  
Coil Transition ◽  
Hydrodynamic Shear ◽  
Linear Shear ◽  
Dynamics Simulations

We study collapsed homo-polymeric molecules under linear shear flow conditions using hydrodynamic Brownian dynamics simulations. Tensile force profiles and the shear-rate-dependent globular-coil transition for grafted and non-grafted chains are investigated to shine light on the different unfolding mechanisms. The scaling of the critical shear rate, at which the globular-coil transition takes place, with the monomer number is inverse for the grafted and non-grafted scenarios. This implicates that for the grafted scenario, larger chains have a decreased critical shear rate, while for the non-grafted scenario higher shear rates are needed in order to unfold larger chains. Protrusions govern the unfolding transition of non-grafted polymers, while for grafted polymers, the maximal tension appears at the grafted end.

Modelization of dispersion of swimming bacteria in Poiseuille flow

2021 ◽  
Author(s):  
Akash Ganesh ◽  
Romain Rescanieres ◽  
Carine Douarche ◽  
Harold Auradou
Keyword(s):  
Shear Rate ◽  
Numerical Simulations ◽  
Poiseuille Flow ◽  
Dispersion Coefficient ◽  
Equations Of Motion ◽  
Critical Shear Rate ◽  
Uniform Shear ◽  
Simple Boundary ◽  
Swimming Bacteria ◽  
Local Shear

&lt;p&gt;We study the shear-induced migration of dilute suspensions of swimming bacteria (modelled as Active elongated Brownian Particles or ABPs) subject to plane Poiseuille flow in a confined channel. By incorporating very simple boundary conditions, we perform numerical simulations of the 3D equations of motion describing the change in position and orientation of the particles. We investigate the effects of confinement, of non-uniform shear and of aspect ratio of the particles on the overall dynamics of the ABPs population.&lt;/p&gt;&lt;p&gt;We particularly study the coupling between the local shear and the change in the orientation of the particles. We thus perform numerical simulations on both the case where the change in the orientation of the ABPs is purely diffusive (decoupled case) and the case where their orientation is coupled to the shear flow (coupled case). We observe that the decoupled case exhibits a Taylor dispersion &lt;em&gt;i.e.&lt;/em&gt;&amp;#160; the effective dispersion coefficient of the ABPs along the direction of the flow is proportional to the square of the imposed shear at all shears.&amp;#160;&lt;/p&gt;&lt;p&gt;However, for all the coupled cases we observe a transition from a Taylor to an active-Taylor regime at a critical shear rate, indicating the effect of shear coupling on the orientation dynamics of the particles. This critical shear rate is directly correlated to the degree of confinement. The change in the dispersion coefficient along the direction of the flow as function of the shear rate is in qualitative agreement with previous studies[1].&amp;#160;&lt;/p&gt;&lt;p&gt;To further understand these results, we also investigate the change in the dispersion coefficient in the other two directions along with the effect of the shape of the particles. We believe that this study should enhance our understanding of dispersion of bacteria through porous media, on surfaces etc. where shear flows are ubiquitous.&amp;#160;&lt;/p&gt;&lt;p&gt;[1] Sandeep Chilukuri, Cynthia H.Collins, and Patrick T. Underhill. Dispersionof flagellated swimming microorganisms in planar poiseuille flow.Physics offluids, 27, (031902):1 &amp;#8211;17, 2015&lt;/p&gt;

Physical Aging and Thixotropy in Sludge Rheology

2008 ◽  
Vol 18 (1) ◽  
pp. 13495-1-13495-8 ◽  
Author(s):  
J.C. Baudez
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Physical Aging ◽  
Abrupt Change ◽  
Rheological Behaviour ◽  
Critical Value ◽  
Solid Content ◽  
Structural Parameter ◽  
Critical Shear Rate ◽  
A New Technique

Abstract Sewage sludge presents a dual rheological behaviour with an abrupt change between the two regimes. Using a new technique of reconstruction of the velocity profile, the behaviour can be modelled by a unique equation including liquid and solid components but also a structural parameter. It is also rigorously demonstrated that the only one rheological behaviour in steady state in the liquid regime is a truncated power-law which can be defined only for a shear rate and a shear stress higher than a critical value, γ̇c and τc. Moreover, the critical shear rate and shear stress increase with the solid content and depend on the fractal dimension of flocs which implies that thixotropic effects are all the more important as the sludge is thick and fresh.

Use of associating polymers as multifunctional thickeners: studies of Their structure in aqueous solutions via nmr, qels, fluorescence, And rheology measurements

2007 ◽  
Vol 29 (5) ◽  
pp. 410-411 ◽  
Author(s):  
Katsunori Yoshida ◽  
Ayano nakamura ◽  
Yuki nakajima ◽  
Tadao Fukuhara ◽  
Haruhiko Inoue ◽  
...  
Keyword(s):  
Aqueous Solutions ◽  
Associating Polymers

A continuum approach to reproduce molecular-scale slip behaviour

2010 ◽  
Vol 645 ◽  
pp. 59-80 ◽  
Author(s):  
H.-Y. HSU ◽  
N. A. PATANKAR
Keyword(s):  
Shear Rate ◽  
Slip Length ◽  
Force Balance ◽  
Wall Region ◽  
Critical Shear Rate ◽  
Mean Velocity ◽  
Compressibility Effect ◽  
Momentum Loss ◽  
Molecular Scale ◽  
Loss Parameter

In this work we explore if it is possible to reproduce molecular-scale slip behaviour by using continuum equations. To that end it is noted that molecular-scale slip is affected by three factors: (i) near the wall, the fluid experiences a potential because of the wall; (ii) the fluid density responds to that potential, and hence, fluid compressibility is relevant; and (iii) the fluid can lose momentum to the wall. To incorporate these features we simulate shear flow of a compressible fluid between two walls in the presence of a potential. Compressibility effect is found to be important only in the near-wall region. The slip length is calculated from the mean velocity profile. The slip-length-versus-shear-rate trend is similar to that in molecular dynamic calculations. First, there is a constant value of the slip length at low shear rates. Then, the slip length increases beyond a critical shear rate. Lastly, the slip length reaches another constant value if the wall momentum loss parameter is non-zero. The scaling for the critical shear rate emerges from our results. The value of the slip length increases if the wall potential is less corrugated and if the momentum loss to the wall is low. An understanding of the overall force balance during various slip modes emerges from the governing equations.

Influence of shear on the structures and properties of regenerated silk fibroin aqueous solutions

RSC Advances ◽  
2015 ◽  
Vol 5 (77) ◽  
pp. 62936-62940 ◽  
Author(s):  
Yuan Jin ◽  
Yichun Hang ◽  
Qingfa Peng ◽  
Yaopeng Zhang ◽  
Huili Shao ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Shear Rate ◽  
Aqueous Solutions ◽  
Crystal Structures ◽  
Silk Fibroin ◽  
Structures And Properties ◽  
Regenerated Silk Fibroin

Regenerated silk fibroin molecules in aqueous solutions gradually form rod-like liquid crystal structures after being applied sufficient shear rate and shear time.

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