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The rheology (from ancient Greek ῥεῖν Rhine , German , flow ' and λόγος logos , German , teaching' ) or floating customer is the science that deals with the deformation - busy and flow behavior of matter. Rheology therefore includes sub-areas of elasticity theory , plasticity theory and fluid mechanics . It deals with both continuum mechanical problems and the derivation of the necessary material laws from the micro or nanostructure of different classes of condensed matter (e.g. macromolecular systems , suspensions ).

As a typical interdisciplinary subject, rheology is in contact with physics , physical chemistry , engineering and materials science and, in the last few decades, with the life sciences and earth sciences .


The rheology can be divided into four areas:

Phenomenological rheology (macrorheology)
This branch describes the deformation and flow behavior of substances without considering the substance structure.
Structural rheology (microrheology)
The phenomena are explained here from the microscopic structure of the substances.
It deals with measurement methods for determining the rheological properties.
Applied Rheology
The knowledge about rheological behavior flows into the design and development of products, technical processes and systems.

A specialty is high temperature rheology. The upper temperature limit for measurements has been raised in recent years from 1600 ° C, achievable in platinum-rhodium crucibles, to 1800 ° C in ceramic crucibles.

History of origin

The Egyptian Amenemhet took into account the temperature dependence of the viscosity of water when designing his water clock in the 16th century BC . A scientific investigation of rheological questions did not take place until the early modern period , in particular by Isaac Newton , who defined the viscosity for Newtonian liquids , and by Robert Hooke , who established the law of elasticity ( Hooke's law ) named after him .

In the 19th century, more work on fluid mechanics was carried out by George Gabriel Stokes , Claude Louis Marie Henri Navier , Gotthilf Hagen and Jean Léonard Marie Poiseuille . At the end of the century, James Clerk Maxwell , William Thomson, 1st Baron Kelvin , John Henry Poynting and others studied viscoelasticity . The work of z. B. Barré de Saint-Venant and Ludwig Prandtl contributed to a deeper understanding of plasticity .

The term rheology for the science that deals with the flow and deformation behavior of matter was only coined at the end of the 1920s by Eugene Cook Bingham , who himself was active in the field of plasticity theory, together with Markus Reiner . The naming was inspired by Heraclitus' aphorism panta rhei (dt. Everything flows ). The chemist Bingham was convinced of the need for a branch of physics that deals with such questions and thus has certain intersections with chemistry and engineering. He told Reiner:

“Here you, a civil engineer, and I, a chemist, work together on common problems. With the development of colloid chemistry , such a situation will appear more and more often. We must therefore found a branch of physics that deals with such problems. "

- Bingham

On August 29, 1929, he and others founded the Society of Rheology in Columbus , Ohio .


Properties of non-Newtonian liquids

Many substances combine properties of a solid ( elasticity ) and a liquid ( viscosity ), which is described by the rheological models . Depending on the experimental conditions, they can elastically cushion external influences on short time scales, but flow away on long time scales. Such behavior is called viscoelastic ; it can be described by a frequency- dependent but still linear summary of elasticity theory and Newtonian hydrodynamics .

Other typical rheological effects, however, are based on non-linear relationships such as the normal stress effect and the Weissenberg effect .

Application examples

The ability of an adhesive to wet a component surface is determined by its rheological properties. The viscosity , thixotropy , structural viscosity , rheopexy and dilatancy are important .

In milling and bakery laboratories Teigprüfgeräte as are Aleurometer , sample size device, farinograph , extensograph or Amylograph used cereal - and flour quality to consider. The resistance of a dough to a constant mechanical load is measured and recorded in the rheometer curve. These can be kneading, stretching or gelatinization tests (with increasing temperature).

In the dairy industry, typical product properties of e.g. B. cream , puddings or desserts can be destroyed if you do not know their flow behavior.

Rocks in the interior of the earth are viscous at greater depths (see asthenosphere ).

Plastics processing

The so-called melt rheology is an important part of rheology. The shear viscosity and sometimes also the extensional viscosity are measured as a function of the shear or elongation rate using various methods. Capillary rheometers and rotational rheometers are most frequently used for the shear viscosity, while only special devices, so-called extensional rheometers , are used for the extensional viscosity . The aim is to gain a better understanding of the processibility of different plastics . Shear-dominated flows are found in an extruder , while in many processes ( fiber spinning , film / hollow body blowing , deep drawing or foaming ), processes with a high degree of stretching dominance take place after the extrusion, which are the most technically demanding and therefore most require an understanding of the material.


In medicine, the flow properties of the blood ( hemorheology ) play a very important role for microcirculation and thus for the supply of all organs with nutrients and oxygen. In particular, the blood flow in the smallest of vessels, the capillaries with a diameter of 4 to 10 µm, is decisively influenced by the rheological properties of the blood. These are mainly determined by the deformability and tendency to aggregate ( roll formation ) of the erythrocytes (mean diameter 7.6 µm), the platelet aggregation , the temperature, the hematocrit and the viscosity of the blood plasma .

As part of the therapy of various circulatory disorders (and alleged circulatory disorders), an improvement in hemorheology is often sought in order to improve microcirculation. These include u. a. the hemodilution and administration of antiplatelet agents in stroke , wherein the AVK and when sudden deafness . However, only the positive effect of platelet aggregation inhibitors in stroke and AVK has been well documented; this can be entirely independent of the rheological effects. However, there is insufficient scientific evidence for the effect on acute hearing loss and other inner ear dysfunction. A rather rare name for drugs that stimulate blood circulation is rheologic (singular: rheologic ).

Printing technology

The rheology of printing inks plays an important role in printing technology. The physical parameters viscosity and flow limit as well as the device size ("tack") largely determine the behavior of the printing ink in the printing machine (ink splitting ), the transfer to the printing material and the quality of the printed product.

Printing inks are thixotropic because they are colloidal systems, i.e. dispersions . The thixotropy is generally undesirable in printing inks.

See also


  • Thomas Mezger: The Rheology Handbook. for users of rotation and oscillation rheometers . 2., revised. Edition. Vincentz Network, Hannover 2006, ISBN 978-3-87870-175-0 . Lothar Gehm: RHEOLOGY - Practice-oriented basics and glossary. VINCENZ 1998, ISBN 3-87870-449-6 .
  • Alexander Ya. Malkin, Avraam I. Isayev: Rheology - concepts, methods and applications. ChemTech Publ., Toronto 2005, ISBN 1-895198-33-X .
  • Robert G. Owens, TN Phillips: Computational rheology. Imperial College Press, London 2002, ISBN 1-86094-186-9 .
  • Roger I. Tanner: Engineering rheology. Oxford Univ. Press, Oxford 2000, ISBN 0-19-856473-2 .

Web links

Scientific journals:

Individual evidence

  1. a b c Hanswalter Giesekus: Phenomenological Rheology. An introduction . Springer, Berlin / Heidelberg / New York 1994, ISBN 3-642-57953-1 , chap. 1, p. 1–4 , doi : 10.1007 / 978-3-642-57953-0 ( limited preview in Google book search).
  2. a b c d Deepak Doraiswamy: The Origins of Rheology: A Short Historical Excursion . In: The Society of Rheology (Ed.): Rheology Bulletin . tape 71 , no. January 2 , 2002 (English, rheology.org [PDF]).