scholarly journals Shear-Thinning in Oligomer Melts—Molecular Origins and Applications

Polymers ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2806
Author(s):  
Ranajay Datta ◽  
Leonid Yelash ◽  
Friederike Schmid ◽  
Florian Kummer ◽  
Martin Oberlack ◽  
...  
Keyword(s):  
Shear Thinning ◽  
Coarse Grained ◽  
Fluid Shear ◽  
Chain Flexibility ◽  
Shear Rates ◽  
Chain Stiffness ◽  
Polymer Flows ◽  
Interchain Interactions ◽  
Coarse Grained Simulations ◽  
Low Shear

We investigate the molecular origin of shear-thinning in melts of flexible, semiflexible and rigid oligomers with coarse-grained simulations of a sheared melt. Entanglements, alignment, stretching and tumbling modes or suppression of the latter all contribute to understanding how macroscopic flow properties emerge from the molecular level. In particular, we identify the rise and decline of entanglements with increasing chain stiffness as the major cause for the non-monotonic behaviour of the viscosity in equilibrium and at low shear rates, even for rather small oligomeric systems. At higher shear rates, chains align and disentangle, contributing to shear-thinning. By performing simulations of single chains in shear flow, we identify which of these phenomena are of collective nature and arise through interchain interactions and which are already present in dilute systems. Building upon these microscopic simulations, we identify by means of the Irving–Kirkwood formula the corresponding macroscopic stress tensor for a non-Newtonian polymer fluid. Shear-thinning effects in oligomer melts are also demonstrated by macroscopic simulations of channel flows. The latter have been obtained by the discontinuous Galerkin method approximating macroscopic polymer flows. Our study confirms the influence of microscopic details in the molecular structure of short polymers such as chain flexibility on macroscopic polymer flows.

The Simulation of Aggregated Colloids Under Flow

1992 ◽  
Vol 289 ◽  
Author(s):  
John R. Melrose
Keyword(s):  
Shear Rate ◽  
Large Scale ◽  
Shear Thinning ◽  
High Shear ◽  
Shear Rates ◽  
Rouse Model ◽  
High Shear Rates ◽  
Structural Breakdown ◽  
Large Scale Simulations ◽  
Low Shear

AbstractAn overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.

scholarly journals Shear-induced orientational dynamics and spatial heterogeneity in suspensions of motile phytoplankton

2015 ◽  
Vol 12 (112) ◽  
pp. 20150791 ◽  
Author(s):  
Michael T. Barry ◽  
Roberto Rusconi ◽  
Jeffrey S. Guasto ◽  
Roman Stocker
Keyword(s):  
Fluid Flow ◽  
Aspect Ratio ◽  
Fluid Shear ◽  
Ambient Flow ◽  
Shear Rates ◽  
Flow Interactions ◽  
Rate Characteristic ◽  
The Rich ◽  
Uniform Fluid ◽  
Low Shear

Fluid flow, ubiquitous in natural and man-made environments, has the potential to profoundly impact the transport of microorganisms, including phytoplankton in aquatic habitats and bioreactors. Yet, the effect of ambient flow on the swimming behaviour of phytoplankton has remained poorly understood, largely owing to the difficulty of observing cell–flow interactions at the microscale. Here, we present microfluidic experiments where we tracked individual cells for four species of motile phytoplankton exposed to a spatially non-uniform fluid shear rate, characteristic of many flows in natural and artificial environments. We observed that medium-to-high mean shear rates (1–25 s −1 ) produce heterogeneous cell concentrations in the form of regions of accumulation and regions of depletion. The location of these regions relative to the flow depends on the cells' propulsion mechanism, body shape and flagellar arrangement, as captured by an effective aspect ratio. Species having a large effective aspect ratio accumulated in the high-shear regions, owing to shear-induced alignment of the swimming orientation with the fluid streamlines. Species having an effective aspect ratio close to unity exhibited little preferential accumulation at low-to-moderate flow rates, but strongly accumulated in the low-shear regions under high flow conditions, potentially owing to an active, behavioural response of cells to shear. These observations demonstrate that ambient fluid flow can strongly affect the motility and spatial distribution of phytoplankton and highlight the rich dynamics emerging from the interaction between motility, morphology and flow.

The effect of shear-thinning behaviour on rod orientation in filled fluids

2016 ◽  
Vol 798 ◽  
pp. 350-370 ◽  
Author(s):  
Julien Férec ◽  
Erwan Bertevas ◽  
Boo Cheong Khoo ◽  
Gilles Ausias ◽  
Nhan Phan-Thien
Keyword(s):  
Cell Model ◽  
Rheological Behaviour ◽  
Shear Thinning ◽  
Shear Rates ◽  
High Shear Rates ◽  
Model Predictions ◽  
The Matrix ◽  
The One ◽  
Good Agreement ◽  
Low Shear

In the present article, the cell model (or self-consistent scheme) is used to derive constitutive equations for rod suspensions in non-Newtonian viscous matrices such as power-law, Ellis and Carreau fluids. It is found that the shear-thinning character of the matrix influences considerably the rod contribution to the stress tensor, but has no impact on the rod orientation dynamics: the same microstructure evolution as the one encountered in Newtonian fluids is obtained. The rod suspension behaves differently than the unfilled matrix in the sense that, depending on rod orientation, the onset of shear thinning in the composite occurs at lower or higher shear rates. Our analysis also provides a semi-analytical model for rod suspensions in an Ellis fluid, which appears to be suitable for predicting a Newtonian plateau at low shear rates and a shear-thinning behaviour at high shear rates. In addition, the model predictions are in good agreement with the shear viscosity measurements of glass-fibre-filled polystyrene melts (Chan et al., J. Rheol., vol. 22 (5), 1978, pp. 507–524), demonstrating its ability to describe the rheological behaviour of such polymer composites. Finally, the proposed approach is extended to a Carreau fluid although its solution requires the numerical solution of a set of partial differential equations.

Grand-Reaction Method for Simulations of Ionization Equilibria and Ion Partitioning in a Broad Range of pH and Ionic Strength

2019 ◽  
Author(s):  
Jonas Landsgesell ◽  
Oleg Rud ◽  
Pascal Hebbeker ◽  
Raju Lunkad ◽  
Peter Košovan ◽  
...  
Keyword(s):  
Mean Field ◽  
Coarse Grained ◽  
Reactive System ◽  
Acid Base ◽  
Buffer Solution ◽  
Reaction Method ◽  
Ionization Equilibria ◽  
Coarse Grained Simulations ◽  
Ph Range ◽  
Weak Polyelectrolytes

We introduce the grand-reaction method for coarse-grained simulations of acid-base equilibria in a system coupled to a reservoir at a given pH and concentration of added salt. It can be viewed as an extension of the constant-pH method and the reaction ensemble, combining explicit simulations of reactions within the system, and grand-canonical exchange of particles with the reservoir. Unlike the previously introduced methods, the grand-reaction method is applicable to acid-base equilibria in the whole pH range because it avoids known artifacts. However, the method is more general, and can be used for simulations of any reactive system coupled to a reservoir of a known composition. To demonstrate the advantages of the grand-reaction method, we simulated a model system: A solution of weak polyelectrolytes in equilibrium with a buffer solution. By carefully accounting for the exchange of all constituents, the method ensures that all chemical potentials are equal in the system and in the multi-component reservoir. Thus, the grand-reaction method is able to predict non-monotonic swelling of weak polyelectrolytes as a function of pH, that has been known from mean-field predictions and from experiments but has never been observed in coarse-grained simulations. Finally, we outline possible extensions and further generalizations of the method, and provide a set of guidelines to enable safe usage of the method by a broad community of users.<br><br>

scholarly journals Rheological properties of hydroxypropylmethyl cellulose/sodium dodecylsulfate mixtures

2014 ◽  
Vol 79 (4) ◽  
pp. 457-468 ◽  
Author(s):  
Jaroslav Katona ◽  
Sandra Njaradi ◽  
Verica Sovilj ◽  
Lidija Petrovic ◽  
Brankica Marceta ◽  
...  
Keyword(s):  
Rheological Properties ◽  
Sodium Dodecylsulfate ◽  
Shear Thinning ◽  
Cellulose Ether ◽  
Flow Profile ◽  
Hydroxypropylmethyl Cellulose ◽  
Shear Rates ◽  
Newtonian Liquids ◽  
Shear Induced Structure ◽  
Induced Structure

Rheological properties of mixtures of hydroxypropylmethyl cellulose (HPMC), a nonionic associative cellulose ether, and sodium dodecylsulfate (SDS), an anionic surfactant, were investigated by viscosity measurements performed at different shear rates (0.1-6000 s-1). HPMC/SDS mixtures containing different concentrations of SDS (CSDS=0.00-3.50 % w/w) and HPMC concentrations which corresponded to the overlap parameter c/c*=3, 6, and 12 were prepared. All HPMC/SDS mixtures were found to be shear-thinning when examined in a low-end-to mid-range of the applied shear rates. The degree of shear-thinning, n, and viscosity of the mixtures were influenced by composition of HPMC/SDS mixtures and HPMC-SDS complex formation. The changes in n ranged from values typical for highly shear thinning to almost perfectly Newtonian liquids, and were more pronounced as c/c* was increased from 3 to 6 and 12. A change in flow profile and a buildup of the first normal stress difference (N1) was observed in HPMC/SDS mixtures with c/c*=6 and 12 and CSDS 0.55-1.00 % and 0.55-2.50 %, respectively, when a critical shear rate, crit. was exceeded, suggesting that a shear-induced structure formation in the mixtures took place.

scholarly journals Prediction and validation of protein intermediate states from structurally rich ensembles and coarse-grained simulations

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Laura Orellana ◽  
Ozge Yoluk ◽  
Oliver Carrillo ◽  
Modesto Orozco ◽  
Erik Lindahl
Keyword(s):  
Coarse Grained ◽  
Intermediate States ◽  
Coarse Grained Simulations

Effect of Blood Viscosity on Thrombosis Potential Near a Step Wall Transition

2009 ◽  
Author(s):  
Scott C. Corbett ◽  
Amin Ajdari ◽  
Ahmet U. Coskun ◽  
Hamid N.-Hashemi
Keyword(s):  
Blood Flow ◽  
Vessel Wall ◽  
Coagulation Factors ◽  
Artificial Organs ◽  
Physical Factors ◽  
Local Geometry ◽  
Induce Platelet Aggregation ◽  
Shear Rates ◽  
Chemical Factors ◽  
Low Shear

Thrombosis and hemolysis are two problems encountered when processing blood in artificial organs. Physical factors of blood flow alone can influence the interaction of proteins and cells with the vessel wall, induce platelet aggregation and influence coagulation factors responsible for the formation of thrombus, even in the absence of chemical factors in the blood. These physical factors are related to the magnitude of the shear rate/stress, the duration of the applied force and the local geometry. Specifically, high blood shear rates (or stress) lead to damage (hemolysis, platelet activation), while low shear rates lead to stagnation and thrombosis [1].

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