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JournalISSN: 0377-0257

Journal of Non-newtonian Fluid Mechanics 

Elsevier BV
About: Journal of Non-newtonian Fluid Mechanics is an academic journal published by Elsevier BV. The journal publishes majorly in the area(s): Newtonian fluid & Viscoelasticity. It has an ISSN identifier of 0377-0257. Over the lifetime, 4330 publications have been published receiving 151941 citations.


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Journal ArticleDOI
TL;DR: A history of thixotropy is given in this article, together with a description of how it is understood today in various parts of the scientific community, and a mechanistic description of the thixotropic system is presented.
Abstract: The ensuing mechanical response to stressing or straining a structured liquid results in various viscoelastic phenomena, either in the linear region where the microstructure responds linearly with respect to the stress and strain but does not itself change, or in the nonlinear region where the microstructure does change in response to the imposed stresses and strains, but does so reversibly. The complication of thixotropy arises because this reversible, microstructural change itself takes time to come about due to local spatial rearrangement of the components. This frequently found time-response of a microstructure that is itself changing with time makes thixotropic, viscoelastic behaviour one of the greatest challenges facing rheologists today, in terms of its accurate experimental characterisation and its adequate theoretical description. Here a history of thixotropy is given, together with a description of how it is understood today in various parts of the scientific community. Then a mechanistic description of thixotropy is presented, together with a series of applications where thixotropy is important. A list of different examples of thixotropic systems is then given. Finally the various kinds of theories that have been put forward to describe the phenomenon mathematically are listed.

1,367 citations

Journal ArticleDOI
TL;DR: In this paper, a constitutive equation is derived from a Lodge-Yamamoto type of network theory for polymeric fluids, where the network junctions are not assumed to move strictly as points of the continuum but allowed a certain "effective slip".
Abstract: A constitutive equation is derived from a Lodge—Yamamoto type of network theory for polymeric fluids. The network junctions are not assumed to move strictly as points of the continuum but allowed a certain “effective slip”. The rates of creation and destruction of junctions are assumed to depend on the instantaneous elastic energy of the network, or equivalently, the average extension of the network strand, in a simple manner. Agreement between model predictions and the I.U.P.A.C. data on L.D.P.E. is good.

1,066 citations

Journal ArticleDOI
TL;DR: In this paper, the authors give an account of the development of the idea of yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time.
Abstract: An account is given of the development of the idea of a yield stress for solids, soft solids and structured liquids from the beginning of this century to the present time. Originally, it was accepted that the yield stress of a solid was essentially the point at which, when the applied stress was increased, the deforming solid first began to show liquid-like behaviour, i.e. continual deformation. In the same way, the yield stress of a structured liquid was originally seen as the point at which, when decreasing the applied stress, solid-like behaviour was first noticed, i.e. no continual deformation. However as time went on, and experimental capabilities increased, it became clear, first for solids and lately for soft solids and structured liquids, that although there is usually a small range of stress over which the mechanical properties change dramatically (an apparent yield stress), these materials nevertheless show slow but continual steady deformation when stressed for a long time below this level, having shown an initial linear elastic response to the applied stress. At the lowest stresses, this creep behaviour for solids, soft solids and structured liquids can be described by a Newtonian-plateau viscosity. As the stress is increased the flow behaviour usually changes into a power-law dependence of steady-state shear rate on shear stress. For structured liquids and soft solids, this behaviour generally gives way to Newtonian behaviour at the highest stresses. For structured liquids this transition from very high (creep) viscosity (>106 Pa.s) to mobile liquid (

950 citations

Journal ArticleDOI
TL;DR: In this paper, a special case of thise theory is given by a model with only one configuration tensor which both the stress and mobility tensors depend on, and a further specialization is introduced by assuming a linear dependency of stress tensors on the configuration tensors.
Abstract: Some time ago a theory of elastic fluids such as concentrated polymer solutions and melts was presented based on the concept of a multitude of penetrating statistical continua. The configurations of these depend on the deformation history, and their relative motion is determined by the coordinated part-stress in connection with a tensorial mobility which is a function of all configuration tensors. The simples special case of thise theory is given by a model with only one configuration tensor which both the stress and mobility tensors depend on. In this paper a further specialization is introduced by assuming a linear dependency of stress as well as of mobility tensors on the configuration tensor. Some relationship to a modified retation model, recently presented by Curtiss and Bird, is hereby established. This model which is of the rate-type and is non-linear in the configuration and stress tensors, respectively, nevertheless permits analytic solutions of some of the most important types of flow. These are explicitly given for both steady and transient extensional and shear flows. Besides shear thinning and non-vanishing first and second normal-stress differences, an extensional viscosity with finite asymptotic values as well as non-exponential stress relaxation and start-up curves are predicted, with stress-overshoot at least in the case of shear flow.

894 citations

Journal ArticleDOI
TL;DR: Slip occurs in the flow of two-phase systems because of the displacement of the disperse phase away from solid boundaries as mentioned in this paper, which arises from steric, hydrodynamic, viscoelastic and chemical forces and constraints acting on the dispersed phase immediately adjacent to the walls.
Abstract: Slip occurs in the flow of two-phase systems because of the displacement of the disperse phase away from solid boundaries. This arises from steric, hydrodynamic, viscoelastic and chemical forces and constraints acting on the disperse phase immediately adjacent to the walls. The enrichment of the boundary near the wall with the continuous (and usually low-viscosity) phase means that any flow of the fluid over the boundary is easier because of the lubrication effect. Because this effect is usually confined to a very narrow layer — with typical thickness of 0.1–10 μm—it so resembles the slip of solids over surfaces that it has historically been given the same terminology. The restoring force for all the forces that cause an increase in concentration is usually osmotic, and this will always limit the effective slip. In dilute systems, concentration gradients can be present over relatively large distances out from walls, giving what might be interpreted on an overall basis as a thick solvent-only layer. However, as the concentration of the system increases, the layer gets thinner and thinner because it is more difficult to create with the large reverse osmotic force present. However, the enormous increase in the bulk viscosity with increase in concentration means that although thinner, the layer becomes, paradoxically, even more important. Slip manifests itself in such a way that viscosity measured in different size geometries gives different answers if calculated the normal way — in particular the apparent viscosity decreases with decrease in geometry size (e.g. tube radius). Also, in single flow curves unexpected lower Newtonian plateaus are sometimes seen, with an apparent yield stress at even lower stresses. Sudden breaks in the flow curve can also be seen. Large particles as the disperse phase (remember flocs are large particles), with a large dependence of viscosity on the concentration of the dispersed phase are the circumstances which can give slip, especially if coupled with smooth walls and small flow dimensions. The effect is usually greatest at low speeds/flow rates. When the viscometer walls and particles carry like electrostatic charges and the continuous phase is electrically conducted, slip can be assumed. In many cases we need to characterise the slip effects seen in viscometers because they will also be seen in flow in smooth pipes and condults in manufacturing plants. This is usually done by relating the wall shear stress to a slip velocity using a power-law relationship. When the bulk flow has also been characterized, the flow in real situations can be calculated. To characterise slip, it is necessary to change the size of the geometry, and the results extrapolated to very large size to extract unambigouos bulk-flow and slip data respectively. A number of mathematical manipulations are necessary to retrieve these data. We can make attempts to eliminate slip by altering the physical or chemical character of the walls. This is usually done physically by roughening or profiling, but in the extreme, a vane can be used. This latter geometry has the advantage of being easy to make and clean. In either case—by extrapolation or elimination—we end up with the bulk flow properties. This is important in situations where we are trying to understand the microstructure/flow interactions.

818 citations

Performance
Metrics
No. of papers from the Journal in previous years
YearPapers
202360
2022122
2021102
2020117
2019123
2018104