View source for Thixotropy

{{Short description|Change in viscosity of a gel or fluid caused by stress}}
[[File:Manuka honey in a bowl.jpg|thumb|[[Mānuka honey]] is an example of a thixotropic material.]]
'''Thixotropy''' is a time-dependent [[shear thinning]] property. Certain [[gels]] or [[fluids]] that are thick or [[viscous]] under static conditions will [[flow (fluid)|flow]] (become thinner, less viscous) over time when shaken, agitated, [[shear stress|shear-stressed]], or otherwise [[stress (mechanics)|stressed]] ([[Viscosity#Newtonian and non-Newtonian fluids|time-dependent viscosity]]). They then take a fixed time to return to a more viscous state.<ref>{{cite encyclopedia|encyclopedia=Kirk-Othmer encyclopedia of Chemical Technology
|author=Morrison, Ian
|year=2003
|doi=10.1002/0471238961.0409191613151818.a01|isbn=978-0471238966
|chapter=Dispersions
}}</ref>
Some [[Non-Newtonian fluid|non-Newtonian]] [[power-law fluid|pseudoplastic]] fluids show a time-dependent change in [[viscosity]]; the longer the fluid undergoes [[shear stress]], the lower its viscosity.  A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some thixotropic fluids return to a gel state almost instantly, such as [[ketchup]], and are called [[pseudoplastic]] fluids. Others such as [[yogurt]] take much longer and can become nearly solid. Many gels and [[colloids]] are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Thixotropy arises because particles or structured solutes require time to organize.<ref name="MewisandWagner">{{cite journal |last1=Mewis |first1=J |last2=Wagner |first2=N J |title=Thixotropy |journal=Advances in Colloid and Interface Science |date=2009 |volume=147-148 |pages=214–227 |doi=10.1016/j.cis.2008.09.005 |pmid=19012872 }}</ref>

Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Fluids which exhibit this property are sometimes called [[rheopecty|rheopectic]]. Anti-thixotropic fluids are less well documented than thixotropic fluids.<ref name="MewisandWagner"/>

== History ==
Many sources of thixotropy comes from the studies of Bauer and Collins as the earliest source of origin. Later in 1923, other researchers began experimenting with thixotropy and then began reporting that many gels consist of aqueous [[Fe2O3|Fe<sub>2</sub>O<sub>3</sub>]] dispersions.

These researchers, Mewis and Barnes, Schalek and Szegvari, and H. Freundlich, then learned that they could make the gel turn into a liquid simply by shaking the contents.  The more that was learned of this material has been found in numerous other products without the realization of the people making said products. <ref name=":0">{{Cite journal |last1=Mewis |first1=Jan |last2=Wagner |first2=Norman J. |date=March 2009 |title=Thixotropy |url=https://linkinghub.elsevier.com/retrieve/pii/S0001868608001735 |journal=Advances in Colloid and Interface Science |language=en |volume=147-148 |pages=214–227 |doi=10.1016/j.cis.2008.09.005|pmid=19012872 |url-access=subscription }}</ref>

==Natural examples==
{{more citations needed|section|date=April 2022}}
[[File:Quicksand (4596511338).jpg|thumb|right|[[Quicksand]] on the shore of the [[River Thames]]. Quicksand demonstrates thixotropy in the form of [[shear thinning]], in that it is solid when at rest, but quickly liquefies when agitated.]]
Some [[clay]]s are thixotropic, influenced by thermochemical treatment, and their behaviour is of great importance in [[structural engineering|structural]] and [[geotechnical engineering]].<ref>{{cite journal |last1=Krupskaya |first1=V. V. |last2=Zakusin |first2=S. V. |last3=Tyupina |first3=E. A. |last4=Dorzhieva |first4=O. V. |last5=Chernov |first5=M. S. |last6=Bychkova |first6=Ya. V. |title=Transformation of Structure and Adsorption Properties of Montmorillonite under Thermochemical Treatment |journal=Geochemistry International |date=March 2019 |volume=57 |issue=3 |pages=314–330 |doi=10.1134/S0016702919030066|bibcode=2019GeocI..57..314K }}</ref><ref>{{cite journal |last1=Ogolo |first1=Oghenerume |last2=Arinkoola |first2=Akeem O. |last3=Ngene |first3=Peter |last4=Ogbaga |first4=Chukwuma C. |last5=Osisanya |first5=Samuel |title=Thermochemical Treatment of Nigerian Raw Clays for Oil and Gas Drilling Operations |journal=ChemEngineering |date=12 November 2023 |volume=7 |issue=6 |pages=110 |doi=10.3390/chemengineering7060110|doi-access=free }}</ref> [[Landslide]]s, such as those common in the [[cliff]]s around [[Lyme Regis]], [[Dorset]] and in the [[Aberfan disaster|Aberfan spoil tip disaster]] in [[Wales]] are evidence of this phenomenon. Similarly, a [[lahar]] is a mass of earth [[Liquefaction|liquefied]] by a [[volcano|volcanic]] event, which rapidly solidifies once coming to rest.

[[Drilling fluid]]s used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions (such as [[Calluna#Uses|heather honey]] or [[mānuka honey]]).

Both [[cytoplasm]] and the [[ground substance]] in the human body are thixotropic, as is [[semen]].<ref>Hendrickson, T: "Massage for Orthopedic Conditions", page 9. Lippincott Williams & Wilkins, 2003.</ref>

Some clay deposits found in the process of exploring [[caves]] exhibit thixotropism: an initially solid-seeming mudbank will turn soupy and yield up moisture when dug into or otherwise disturbed. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment.

A thixotropic fluid is best visualised by an oar blade embedded in mud. Pressure on the oar often results in a highly viscous (more solid) thixotropic mud on the high pressure side of the blade, and low viscosity (very fluid) thixotropic mud on the low pressure side of the oar blade. Flow from the high pressure side to the low pressure side of the oar blade is non-Newtonian. (i.e., fluid velocity is not linearly proportional to the square root of the pressure differential over the oar blade).

==Applications==
{{more citations needed|section|date=April 2022}}
Many kinds of paints and inks—e.g., [[plastisol]]s used in [[silkscreen]] [[textile printing]]—exhibit thixotropic qualities.<ref>{{cite encyclopedia|encyclopedia=Ullmann's Encyclopedia Of Industrial Chemistry|author1=Köhler, Klaus|author2=Simmendinger, Peter|author3=Roelle, Wolfgang|author4=Scholz, Wilfried|author5=Valet, Andreas|author6=Slongo, Mario|year=2010|doi=10.1002/14356007.o18_o03|isbn=978-3527306732|chapter=Paints and Coatings, 4. Pigments, Extenders, and Additives}}</ref> In many cases it is desirable for the fluid to flow sufficiently to form a uniform layer, then to resist further flow, thereby preventing sagging on a vertical surface. Some other inks, such as those used in [[CMYK]]-type process printing, are designed to regain viscosity even faster, once they are applied, in order to protect the structure of the dots for accurate color reproduction.

There are several methods to using thixotropy; one method, the most popular way, is to use a two-phase mixture to model to allow the mixture to continue without added equations entering when thixotropy is working through its process on the different materials.<ref name=":12">{{Cite journal |last1=Wen |first1=Pengpeng |last2=Feng |first2=Zhongjun |last3=Zheng |first3=Baicun |date=August 2023 |title=Thixotropy of fresh cement pastes in presence of cationic polymer |url=https://linkinghub.elsevier.com/retrieve/pii/S0950061823020184 |journal=Construction and Building Materials |language=en |volume=394 |article-number=132302 |doi=10.1016/j.conbuildmat.2023.132302|url-access=subscription }}</ref>

Thixotropic ink (along with a gas pressurized cartridge and special shearing ball design) is a key feature of the [[Fisher Space Pen]], used for writing during zero gravity space flights by the US and Russian space programs.

[[Solder paste]]s used in electronics manufacturing printing processes are thixotropic.

[[Thread-locking fluid]] is a thixotropic adhesive that cures anaerobically.

Thixotropy has been proposed as a scientific explanation of blood liquefaction [[miracle]]s such as that of [[Saint Januarius]] in [[Naples]].<ref>{{cite journal |last1=Garlaschelli |first1=L |last2=Ramaccini |first2=F |last3=Della Scala |first3=S |title=The Blood of St. Januarius |journal=Chemistry in Britain |date=1994 |volume=30 |issue=2 |page=123 |url=http://www.cicap.org/new/articolo.php?id=101014}}</ref>

Semi-solid casting processes such as [[thixomoulding]] use the thixotropic property of some alloys (mostly [[light metal]]s like magnesium). Within certain temperature ranges and with appropriate preparation, an alloy can be put into a semi-solid state, which can be injected with less shrinkage and better overall properties than by normal [[injection molding]].

[[Fumed silica]] is commonly used as a [[rheology]] agent to make otherwise low-viscous fluids thixotropic. Examples range from foods to epoxy resin in structural bonding applications like [[Fillet (mechanics)|fillet joints]].

== Common use ==
Thixotropy has shown to be useful in many ways concerning cement paste. The thixotropy allows the cement to be broken down in a way that allows the user to slowly put down the paste in a controlled manner so it can then be set and dry.<ref name=":2">{{Cite journal |last1=Ojeda-Farías |first1=O. |last2=Hebraud |first2=P. |last3=Lootens |first3=D. |last4=Liard |first4=M. |last5=Mendoza-Rangel |first5=J.M. |date=July 2019 |title=Thixotropy of reactive suspensions: The case of cementitious materials |url=https://linkinghub.elsevier.com/retrieve/pii/S0950061819308189 |journal=Construction and Building Materials |language=en |volume=212 |pages=121–129 |doi=10.1016/j.conbuildmat.2019.03.319|url-access=subscription }}</ref>

Thixotropy is also used in drilling fluids due to their rheological makeup. This however is connected to drilling hydraulics and how thixotropy affects the process of hydraulics.<ref name=":3">{{Cite journal |last1=Gulraiz |first1=Shiraz |last2=Gray |first2=K.E. |date=December 2020 |title=Thixotropy effects on drilling hydraulics |url=https://linkinghub.elsevier.com/retrieve/pii/S1875510020305072 |journal=Journal of Natural Gas Science and Engineering |language=en |volume=84 |article-number=103653 |doi=10.1016/j.jngse.2020.103653|bibcode=2020JNGSE..8403653G |url-access=subscription }}</ref>

== Negative effects ==
While thixotropy has been seen to benefit in areas pertaining to clay and cement, the material also comes with many harmful effects. To try and prevent thixotropy from fracturing the sustainability of the concrete, catatonic polymer began to be used in order to counteract the thixotropy, however this agent is needed in order to allow the mixing of the clay and cementitious material.<ref name=":1">{{Cite journal |last1=Wen |first1=Pengpeng |last2=Feng |first2=Zhongjun |last3=Zheng |first3=Baicun |date=August 2023 |title=Thixotropy of fresh cement pastes in presence of cationic polymer |url=https://linkinghub.elsevier.com/retrieve/pii/S0950061823020184 |journal=Construction and Building Materials |language=en |volume=394 |article-number=132302 |doi=10.1016/j.conbuildmat.2023.132302|url-access=subscription }}</ref> There is now no true way to counteract the effect of thixotropy while also allowing it to break down the materials in the cement and clay.

==Etymology==
The word comes from [[Ancient Greek]] θίξις ''thixis'' 'touch' (from ''thinganein'' 'to touch') and ''-tropy'', ''-tropous'', from Ancient Greek -τρόπος ''-tropos'' 'of turning', from τρόπος ''tropos'' 'a turn', from τρέπειν ''trepein'', 'to turn, change'.<ref>{{OEtymD|thixotropy}}</ref><ref>{{LSJ|qi/cis|θίξις}}, {{LSJ|qigga/nw|θιγγάνειν}}, {{LSJ|troph/|τροπή}}, {{LSJ|tre/pw|τρέπειν|ref}}.</ref> Hence, it can be translated as something that turns (or changes) when touched.  It was invented by [[Herbert Freundlich]] originally for a [[sol-gel]] transformation.<ref name=Reiner>Reiner, M; Scott Blair, G W (1967) in Eich, F. R., (ed) ''Rheology, Theory and Applications'' Vol 4 p 465 (Academic Press, NY)</ref>

==See also==
* [[Bingham plastic]]
* [[Calcium Sulfate]]
* [[Kaye effect]]
* [[Nanocellulose]]
* [[Polymer]]
* [[Silly putty]]
* [[Time-dependent viscosity]]

==References==
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==External links==
*{{Wiktionary-inline}}

{{Geotechnical engineering|state=collapsed}}
{{Non-Newtonian fluids}}
[[Category:Continuum mechanics]]
[[Category:Fluid dynamics]]
[[Category:Non-Newtonian fluids]]
[[Category:Soil mechanics]]
[[Category:Soil physics]]
[[Category:Tribology]]