Effect of temperature on rheological properties of suspensions

A parameter, the product of viscosity of the suspension medium and applied shear rate, is introduced to describe the effect of temperature on the rheological properties of suspensions, considering the mechanism of agglomeration in suspensions. It is found that, by plotting rheograms of the shear stress versus this parameter, a single master curve can be obtained independently of temperature. The dependence of viscosity on temperature and the flow of suspensions are shown to be well described.     

升温速率与流变特性对B炸药慢烤响应的影响

为探究慢速烤燃过程中不同升温速率下B炸药流变特性的尺寸效应对相变后内部温度场的分布特征与点火位置的影响,设计了$\varnothing $76 mm与$\varnothing $130 mm两种尺寸的烤燃弹。通过慢烤试验分别获得了1 ℃/min与3.3 ℃/h两种升温速率下,各烤燃弹内部监测点的温度变化曲线,结合数值模拟进一步分析了各工况下烤燃弹内部温度场的变化特点。研究结果表明：在升温速率为1 ℃/min时,两种尺寸的烤燃弹在炸药还未完全相变前就已发生响应,对流的存在导致炸药顶部的熔化速率明显高于底部,B炸药流变特性的尺寸效应不明显;当升温速率为3.3 ℃/h时,相变完成后,尺寸偏小的烤燃弹内部流场强度低,温度场变化十分缓慢,而尺寸偏大的烤燃弹内部流场强度较大,温度场很快体现出典型的液相温度场分布特征,B炸药的流变特性具有明显的尺寸效应;无论升温速率的快慢与尺寸的大小,炸药发生相变后温度最高点、自热反应区域与最终响应区域都出现在药柱顶部附近。

     

The rheological properties of saliva

Summary Saliva is a complex biological fluid that cannot be effectively studied by conventional methods such as theFerranti-Shirley Viscometer. Testing with theWeissenberg Rheogoniometer shows that saliva is viscoelastic and that the dynamic viscosity falls from 400-0.1 Poise over the frequency range 2.5×10^–3 to 10 Hertz. The calculated elastic contribution can be correlated with dry weight content.Dynamic viscosity and shear modulus are both reduced in storage, by proteolytic enzymes. The mucolytic agent Ascoxal also brings about a reduction in these parameters but by a different mechanism. A comparison of the results with those obtained previously for sputum, shows, that saliva may be a suitable model system for assessing mucolytic agentsin vitro.

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Zusammenfassung Speichel ist eine komplexe biologische Flüssigkeit, die mit konventionellen Methoden, wie z. B. demFerranti-Shirley-Viskosimeter, nicht umfassend untersucht werden kann. Studien mit einemWeissenberg-Rheogoniometer zeigen, daß Speichel viskoelastisch ist und daß seine dynamische Viskosität über einen Frequenzbereich von 2,5 · 10^–3 bis 10 Hz von 400 Poise auf 0,1 Poise fällt. Die berechnete elastische Komponente kann mit dem Trockengewichtsanteil korreliert werden.Dynamische Viskosität und Schermodul werden gemeinsam bei Lagerung von proteolytischen Enzymen reduziert. Das mukolytisch aktive Ascoxal reduziert auf andere Art ebenfalls diese Parameter. Ein Vergleich dieser Ergebnisse mit denen, die für Sputum erhalten werden, zeigt, daß Speichel ein günstiges Modellsystem ist, um mukolytisch aktive Stoffe in vitro zu testen.

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Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14–15, 1970.     

The rheological properties of the arterial wall

Key words The rheological properties of rat arteries were studied in vitro. Using intact arterial segments undergoing large deformations in longitudinal and circumferential direction, both the stress-strain relationship and the corresponding histological changes with deformation are presented. Correlations between the mechanical properties and the histological structure are discussed.     

The effect of dissolved polymers on the rheological properties of coating colours

Coating colours used for the coating of paper and board consist mainly of a mineral pigment, which is very often clay, a synthetic binder such as a styrenebutadiene latex, dispersion agents and water retention aids. The latter are often water soluble polymers. These polymers have a very strong influence on the rheological properties of the coating colours, both on the strain rate dependence of the apparent viscosity and on the viscoelasticity. The effects of two different grades of carboxymethylcellulose (CMC) and one grade of hydroxyethylcellulose (HEC), on the rheological properties at room temperature of a clay-based coating colour at pH 8, have been investigated. It is concluded that the high values of the dynamic modulus of the colours are due to interactions between the cellulose derivatives and the solid particles, i.e. mainly the clay particles. For HEC this interaction is associated with adsorption of the polymeric molecules on the clay particles. In the case of CMC, the adsorption is strongly retarded by the presence of the dispersant (a polyacrylate salt). It is suggested that the marked elasticity of the CMC-containing colour in addition to a possible polymer adsorption may be due to charge interactions and/or depletion flocculation. The effect of CMC and HEC on the water-retention properties of the colour is also discussed.     

The influence of flow confinement on the rheological properties of complex fluids

The rheological properties of plastic and viscoplastic complex fluids have been investigated using constant velocity squeeze flow rheometry at small gaps in order to examine the influence of the resulting flow confinement. The fluids investigated were aqueous carbopol suspensions and three commercial products (Tesco English mustard, Tesco value lemon curd and Heinz tomato ketchup (HTK)). The bulk rheological properties were measured using parallel plate rheometry. Rough plates were used to eliminate wall slip in both rheometric configurations. The commercial products are Herschel–Bulkley fluids and, for gaps less than a critical value of ~200 μm, the yield stresses tended to large values. There was a corresponding trend to small values for the flow consistencies except for HTK, which has a negligibly small bulk value. A possible explanation is that the micro-structural correlation lengths of these fluids are of the order of that of the critical separation. The yield stresses of the carbopol suspensions also increased sharply at the critical gap but then decreased gradually with decreasing gap separation. The transition may correspond to the formation of a jammed state with the subsequent plastic flow at smaller gap separations arising from localised shearing.     

The rheological properties of solder and solar pastes and the effect on stencil printing

Solar and solder pastes are widely used in the electronics industry. Solder paste is the principal joining medium in the assembly of surface mount components, whilst solar paste is used in the manufacture of semiconductor solar cells in the photo-voltaic industry. The stencil printing of both solder and solar pastes is a very important and critical stage in the assembly process. With miniaturisation of components, this is likely to continue. The challenge in stencil printing at such dimensions is in achieving repeatable deposition of both solar and solder pastes from print to print. To meet this challenge requires an understanding of the flow behaviour of both solar and solder pastes. The rheological properties of solar and solder pastes have been evaluated through three different types of experiments. Existing models were applied to compare their rheological behaviour under these schemes. One striking difference was that solar paste showed a higher viscosity than solder paste. Both solar and solder pastes were found to be non-Newtonian materials, showing a decrease in viscosity with increasing shear rates. In this paper we investigate the rheological properties of both solder and solar paste under steady shear and creep-recovery tests. Received: 12 October 1999 Accepted: 11 July 2000     

Effects of temperature and pressure on the rheological behavior of montmorillonite sols

Summary The effects of high temperatures up to 180 C and high pressures up to 560 kg/cm² on the rheological properties of pure montmorillonite suspensions with well-defined base-exchange cations have been investigated. The suspensions behave very much asBingham plastics according to the equation=+, in which is the shear stress,D the shear rate, the plastic viscosity, and the yield stress which is largely a measure of residual flocculation.The observed effects depend strongly on the interparticle forces that govern the colloidal stability and the rheological behavior of the suspensions. One can distinguish between two categories of suspensions:P-type sols in which the clay particles are associated through Coulombic attraction between positive edges and negative faces and are located in a primary potential energy minimum, andS-type sols in which the particles are associated edge-to-edge and are located in a weaker secondary potential minimum obtained by the summation ofvan der Waals attraction and double layer repulsion.Both theBingham yield stress and the plastic viscosity of theP-type sols decrease with increasing temperature. The temperature dependence of follows theArrhenius equation. TheP-type suspensions are either weakly or not at all thixotropic at room temperature and are definitely non-thixotropic at higher temperatures. Pressure slightly increases both the plastic viscosity and the yield stress.TheS-type sols, on the other hand, display an increase in yield stress and degree of thixotropy with increasing temperature and generally a decrease in the plastic viscosity. This behavior is modified in the case of Ca-montmorillonite suspensions, in which both and pass through a maximum at 150C, followed by a decline. The maximum can be explained by disaggregation of face-to-face aggregated clay packets.Pressure causes a decrease both in and the degree of thixotropy in theS-type suspensions, while it causes a slight increase in the plastic viscosity. This behavior is a consequence of the destruction of the hydration shell caused by high pressure.

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Zusammenfassung Der Einfluß von hohen Temperaturen (bis 180 C) und hohen Drucken (bis zu 560 kp/cm²) auf die rheologischen Eigenschaften reiner Suspensionen von Montmorillonit mit definierten Austauschionen wurde untersucht. Die Suspensionen folgen dem Binghamschen Flie\gesetz gemÄ\ der Gleichung=+, worin die Schubspannung,D das GeschwindigkeitsgefÄlle, dieBingham- ViskositÄt und die Flie\spannung darstellen. Letztere zeigt in erster Linie das Ausma\ der Koagulation an.Die beobachteten Effekte hÄngen stark von den KrÄften zwischen den Teilchen ab, welche die StabilitÄt der Kolloide und das rheologische Verhalten der Suspensionen bestimmen. Man kann zwei Kategorien von Suspensionen unterscheiden: Sole vom sog.P-Typ, in denen die Tonteilchen durch Coulombsche AnziehungskrÄfte zwischen positiven Kanten und negativen FlÄchen assoziiert sind und sich in einem primÄren Potentialminimum befinden, und Sole vomS-Typ, in denen die Teilchen Kante-zu-Kante assoziiert sind und sich in einem flacheren sekundÄren Potentialminimum befinden, welches durch das Zusammenwirken vonvan der Waalsschen AnziehungskrÄften und von Absto\ungskrÄften infolge der Wechselwirkung der elektrischen Doppelschichten entsteht.Sowohl die Flie\grenze als auch dieBingham-ViskositÄt der Sole vomP-Typ nehmen mit wachsender Temperatur ab. Die TemperaturabhÄngigkeit von folgt derArrhenius-Gleichung. Die Suspensionen vomP-Typ sind bei Zimmertemperatur entweder gar nicht oder nur schwach thixotrop, wÄhrend sie bei hoher Temperatur in keinem Fall thixotrop sind. Mit wachsendem Druck erhöht sich sowohl dieBingham-ViskositÄt als auch die Flie\grenze ein wenig.Bei den Solen vomS-Typ andererseits steigt die Flie\spannung und der Grad der Thixotropie mit steigender Temperatur, wÄhrend dieBingham-ViskositÄt im allgemeinen abnimmt. Bei Ca-Montmorillonit-Suspensionen ist das Verhalten etwas anders: Sowohl als auch erreichen bei 150 C ein Maximum und fallen dann wieder ab. Das Maximum kann durch Desaggregation flÄchenhaft aggregierter Tonpartikel erklÄrt werden. Bei steigendem Druck fÄllt sowohl als auch der Grad der Thixotropie in den Suspensionen vomS-Typ ab, wÄhrend dieBingham-YiskositÄt leicht ansteigt. Dieses Verhalten ist eine Folge der dann eintretenden Zerstörung der Solvathüllen.

     

The effect of liquid crystal structure on the rheological properties of nitrocellulose-dimethylacetamide solutions

Solutions of Pyro grade nitrocellulose (NC) in dimethyl acetamide (DMA), containing between 42.5% and 60% NC (w/w), have been studied by differential scanning calorimetry and polarised light microscopy. The results showed that NC forms a lyotropic liquid crystal structure in DMA. A transition from the liquid crystal phase to an isotropic phase occurred over the temperature range 27 °C to 67 °C, and the enthalpy of transition increased with NC concentration. Rheological properties were determined using an extrusion rheometer with a slit die. The solutions were shown to have a yield stress for flow which increased with increasing NC concentration. The solutions were also found to be thixotropic.     

The examination and interpretation of the properties of fibres using rheological measurements on non-uniform fibres

Summary Stress-strain, creep and torque-twist measurements on a large number of wool fibres of varying type are used to illustrate how fibre non-uniformities affect the observed behaviour and how the fibre material behaviour is extracted from the measurements. In this regard the concept of effective area of a cross-section is introduced in order to simplify the analysis. It is shown that fibre non-uniformities may hide the effects of certain structural features and if reasonably uniform fibres are not available it may not always be possible to derive the true material behaviour. Variation of properties between fibres can be useful in deriving significant structural information about the fibre material.With 7 figures and 2 tables     

The hydrodynamics of materials whose rheological properties are complicated

Conclusion One of the main problems of the rheologist is the characterization of new materials that are rheologically complicated by means of equations of state which can be used under all conditions of motion and of stress. Then, by solving the equations of state in conjunction with equations of motion and of continuity, he can make predictions about the behaviour of a material in bulk under various imposed external conditions. By comparing the results of his calculations with new experimental observations he can test the accuracy of the equations of state and if necessary modify them to bring them nearer to reality; then the process can be repeated. Progress, in this as in other branches of science, requires the close collaboration of theoretician and experimentalist.General lecture delivered at the Third International Congress on Rheology, Bad Oeynhausen, September 1958.     

The rheological properties of AgI and Li2SO4 solid electrolytes,I.

Summary The plastic deformations of the high-temperature modifications of AgI and Li₂SO₄ have been studied with a rotational viscometer between 640 and 829 K and between 1054 and 1133 K, respectively. Thixotropic behaviour was observed and the regeneration times were 24 h for AgI at 809 K and 8.4 h for Li₂SO₄ at 1054 K. A change in the yield mechanism in AgI is indicated at the cation order-disorder transition point 705 K. The activation parameters will be discussed in a following paper.

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Zusammenfassung Die plastische Deformierbarkeit der Hochtemperatur-Modifikationen von AgJ und Li₂SO₄ wurde mit einem Rotations-Viskosimeter zwischen jeweils 640 und 829 K bzw. 1054 und 1133 K bestimmt. Es wurde thioxotropes Verhalten gefunden. Die Regenerationszeiten waren für AgJ bei 809 K 24 h und für Li₂SO₄ bei 1054 K 8.4 h. Eine Veränderung des Fließmechanismus wird am Kationen-Ordnungs-Unordnungs-(order-disorder)Umwandlungspunkt bei 705 K gefunden. Die Aktivierungs-Parameter sollen in einer folgenden Publikation diskutiert werden.

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With 10 figures and 3 tables     

The rheological properties of AgI and Li2SO4 solid electrolytes,II.

Summary The plastic deformation of the superionic conductors AgI, Li₂SO₄, and Li₂SO₄–K₂SO₄ mixtures rich in Li₂SO₄ has been investigated using stress relaxation. The observed activation volume is inversely proportional to the effective initial stress, but the proportionality constant is smaller than in normal non-superionic substances. This fact can be attributed to the weak steric hindrance for rotation of the lattice units, making the rotatorphases into an additional exception to the general empirical relation found by Kubát and coworkers.The existence of an order-disorder transition in AgI close to 700 K is confirmed by the stress relaxation data and also by measurements of maximum shear stress versus maximum shearing rate. It is found that such data may be conveniently represented by doubly logarithmic plots, in which a change in flow properties can be easily spotted.With 13 figures and 7 tables     

The impact of blue organic and inorganic pigments on the crystallization and rheological properties of isotactic polypropylene

Viscosity behavior is used to illustrate the relative sensitivity of the rheological properties to the morphological structure imposed by the presence of organic copper phthalocyanine and inorganic ultramarine blue pigments in isotactic polypropylene. While the inorganic pigment showed a small effect, the organic pigment was responsible for greatly increasing the nucleation rate and rapidly increasing the viscosity. This was also accompanied by a lowering of the degree of supercooling and the formation of a fibrous morphology. The results indicate that copper phthalocyanine is an excellent nucleating agent, drastically reducing the onset time of crystal formation and increasing the crystallization kinetics. Dynamic rheological properties also suggest that the organic pigment acts as a softening agent in the supercooled melt. Percent concentration and shear rate were not found to be major factors accelerating the rate of crystallization. This study details contributing factors including the particle size differences of the pigments under scanning electron microscopy, which provides further insight into the non-spherulitic morphology observed under a Linkam device. A possible correlation between the pigment morphology, the crystallization kinetics and rheology is discussed.     

Mechanics of submerged jet cavitating action: material properties,exposure time and temperature effects on erosion

Experimental setup with a submerged cavitating jet has been used for the study of influences of material, exposure time and working fluid temperature on the erosion process. Each of the parameters has been varied separately, and the results of erosion are analyzed in detail. Additionally, comparison of experiments with nitrated and non-nitrated material has been made in order to study the enhancement (mostly reflected as the prolonged incubation time) of erosion resistance achieved by nitrating the specimen surface.