Rheometry

{{Short description|Experimental techniques used to study fluid flow (rheology)}}

{{Continuum mechanics|cTopic=rheology}}

{{Wiktionary}}

Rheometry ({{ety|el|ῥέος (rheos)|stream}}) generically refers to the experimental techniques used to determine the rheological properties of materials,{{Cite book|title=Rheology: Concepts, Methods and Applications|last1=Malkin|first1=Aleksandr I︠A︡kovlevich|last2=Malkin|first2=Alexander|last3=Isayev|first3=Avraam|date=2006|publisher=ChemTec Publishing|isbn=9781895198331|location=Toronto|pages=241}} that is the qualitative and quantitative relationships between stresses and strains and their derivatives. The techniques used are experimental. Rheometry investigates materials in relatively simple flows like steady shear flow, small amplitude oscillatory shear, and extensional flow.{{Cite book|title=Rheology - Volume I|last=Gallegos|first=Crispulo|publisher=EOLSS Publications/UNESCO|year=2010|isbn=9781848267695|location=London|pages=7–8|language=en}}

The choice of the adequate experimental technique depends on the rheological property which has to be determined. This can be the steady shear viscosity, the linear viscoelastic properties (complex viscosity respectively elastic modulus), the elongational properties, etc.

For all real materials, the measured property will be a function of the flow conditions during which it is being measured (shear rate, frequency, etc.) even if for some materials this dependence is vanishingly low under given conditions (see Newtonian fluids).

Rheometry is a specific concern for smart fluids such as electrorheological fluids and magnetorheological fluids, as it is the primary method to quantify the useful properties of these materials.{{citation needed|date=December 2017}}

Rheometry is considered useful in the fields of quality control, process control, and industrial process modelling, among others. For some, the techniques, particularly the qualitative rheological trends, can yield the classification of materials based on the main interactions between different possible elementary components and how they qualitatively affect the rheological behavior of the materials.{{Cite book|title=Rheometry of Pastes, Suspensions, and Granular Materials: Applications in Industry and Environment|url=https://archive.org/details/rheometrypastess00cous|url-access=limited|last=Coussot|first=Philippe|publisher=Wiley-Interscience|year=2005|isbn=9780471653691|location=Hoboken, NJ|pages=[https://archive.org/details/rheometrypastess00cous/page/n17 2]}} Novel applications of these concepts include measuring cell mechanics in thin layers, especially in drug screening contexts.{{Cite journal |last1=Bashir |first1=Khawaja Muhammad Imran |last2=Lee |first2=Suhyang |last3=Jung |first3=Dong Hee |last4=Basu |first4=Santanu Kumar |last5=Cho |first5=Man-Gi |last6=Wierschem |first6=Andreas |date=2022-06-23 |title=Narrow-Gap Rheometry: A Novel Method for Measuring Cell Mechanics |journal=Cells |volume=11 |issue=13 |pages=2010 |doi=10.3390/cells11132010 |issn=2073-4409 |pmc=9265971 |pmid=35805094 |doi-access=free }}