G. W. Scott Blair

The success of Casson's equation

Many diverse materials, including some which are very unlikely to have a structure such as is postulated byCasson, obey his equation for shear-thinning plastic bodies. When the data range over only one or one and a half decades, as is usual, the curves cannot be visually distinguished from those using theHerschel andBulkley equation for which some explanation, depending much less on any specific type of structure, is already available. It also seems probable that the two equations are indistinguishable if both are transformed to allow for small “negative yield-values” in dilatant systems.

Comparative observations on adherence and consistency of various blood systems in living and artificial capillaries

The apparent viscosity of blood, plasma and serum, as measured in theScott Blair (frame) capillary viscometer, is found to be appreciably lower in fibrin coated capillaries than in glass capillaries. This phenomenon, which is probably associated with an enhanced sigma effect, is found in blood of man, cow, rabbit and horse.

Capillary flow and wall adherence of bovine blood, plasma and serum in contact with glass and fibrin surfaces

Summary1.Procedures and treatment of data for the measurement of the apparent viscosity and wall adherence of bovine blood, plasma and serum in contact with glass and fibrin surfaces in capillaries are described.2.Blood and, in many cases, plasma and serum, exhibited non-Newtonian behaviour on both glass and fibrin surfaces.3.The flow behaviour could be represented conveniently in linear form by plotting the square root of the rate of shear against the square root of the stress at the wall.4.Blood on fibrin surfaces exhibited the sigma effect, i. e. anomalies with changes in capillary dimension, more markedly than on glass surfaces.5.The apparent viscosity and wall adherence on fibrin surfaces was always less than on glass.6.Experiments were done on blood from ten cows. Heparin was used as anticoagulant. No consistent differences were observed between blood from the mammary and jugular veins, nor between that from lactating and non-lactating animals.Zusammenfassung1.Apparate und Behandlungsart der Proben zur Messung der scheinbaren Viskosität und der Wandhaftung von Rinderblut, Plasma und Serum in Kontakt mit Glas und Fibrinoberflächen in Kapillaren wird beschrieben.2.Blut und meist auch Plasma und Serum zeigen in beiden Fällen, sowohl in Kontakt mit Glaswand und Fibrinwand nicht-Newtonsches Verhalten.2.Das Fließverhalten kann in üblicher Weise linear dargestellt werden, wenn man die Quadratwurzel aus der Schergeschwindigkeit gegen die Quadratwurzel aus der Scherspannung an der Wand aufträgt.4.Blut an Fibrinflächen zeigt den Sigmaeffekt — das sind Anomalien bei Veränderung der Kapillardimension — ausgeprägter als an Glasflächen.5.Die scheinbare Viskosität und die Wandhaftung an Fibrinflächen ist stets geringer als die an Glas.6.Die Versuche wurden mit Blut von 10 Kühen durchgeführt. Als Antikoagulant wurde Heparin verwendet. Es wurden keine systematischen Unterschiede zwischen Blut aus Brust- und Halsvenen, ebensowenig wie zwischen solchem von milchgebenden und nichtmilchgebenden Tieren gefunden.

A model to describe the flow curves of concentrated suspensions of spherical particles

The explanation for the very common phenomenon of linearity of double logarithmic plots of stress and shear-rate for shear-thinning concentrated suspensions, proposed in earlier papers, has been much extended. A definite model is proposed which, while not claiming to describe real systems in detail, leads to the linearity of the log-log curves and probably represents fairly well the actual behaviour of such systems as thick fresh dairy creams at low temperatures.

On the use of power equations to relate shear-rate to stress in non-Newtonian liquids

SummaryIt is shown that some quite simple assumptions about the nature of the flow of non-Newtonian liquids lead to the use of the well-known power relation between shear-rate and stress, hitherto regarded as entirely empirical. The treatment is applicable both to thinning and to thickening liquids provided there is no hysteresis.

Comparative observations on adherence and consistency of various blood systems in living and artificial capillaries. II: Additional note to a previous paper

SummaryThe apparent viscosity of blood, plasma and serum, as measured in theScott Blair (frame) capillary viscometer, is found to be appreciably lower in fibrin coated capillaries than in glass capillaries. This phenomenon, which is probably associated with an enhanced sigma effect, is found in blood of man, cow, rabbit and horse.Silicone treated surfaces, though not so reliable, show a possibly significant but very much smaller reduction in apparent viscosity.Since, during life, fibrin in some form probably covers the inner lining of blood vessel walls, the phenomenon here described must constitute an important factor in aiding blood circulation.

An extension of Reiner's “Deborah Number” concept to a Wide field of rheological investigations

Reiner defined a numeric, which he called “theDeborah Number” to represent the ratio of a relaxation time to a “natural” (observation) time. This implies aMaxwell model but is readily extended to complete relaxation spectra. Similar Numbers are proposed for retardation times and also for some conditions of coagulation thixotropy and for data from certain psychophysical experiments.

Mathematics and Rheology

The great advances made in Rheology during the last forty years owe much to the application of mathematics. But in some cases, there have been misunderstandings. As a result, rheologists have sometimes been unnecessarily restricted. Mathematics is limited only by self-consistency: Rheology deals with the physical world.

Note on the paper by C. Oiknine and F. Azelvandre in Rheol. Acta 14, 51–52 (1975)

Letters to the Editors (Short Communications) are to ensure the priority of your findings. The responsibility for its contents is absolutely yours. These papers will be published approximately within 2 6 weeks after receipt. Such papers should not exceed 2 pages typewritten. Please, do write your manuscript as clear as possible, especially with respect to formulas! Please, do avoid figures! Should they be inevitable for understanding, please, attach clear drawings by India ink, ready for reproduction. You will receive 75 reprints free of charge. Papers should be submitted directly to: Prof.Dr.H.Giesekus, Abteilung Chemietechnik der Universität Dortmund, Postfach 500 500, D-4600 Dortmund 50.

Presentation of the Poiseuille gold medal of the international society of biorheology to Prof. A. L. Copley, Lyon, France, 1972

Mesdames et Messieurs; Ladies and Gentlemen; Meine Damen und Herren: It is for me a great honour to be invited to present the Poiseuille Gold Medal of our Society to my old friend, Al Copley, Professor Copley was rightly chosen by an overwhelming majority of our members to be the third recipient of this medal.