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Thixotropy

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(Redirected fromThixotropic)
Change in viscosity of a gel or fluid caused by stress
Mānuka honey is an example of a thixotropic material.

Thixotropy is a time-dependentshear thinning property. Certaingels orfluids that are thick orviscous under static conditions willflow (become thinner, less viscous) over time when shaken, agitated,shear-stressed, or otherwisestressed (time-dependent viscosity). They then take a fixed time to return to a more viscous state.[1]Somenon-Newtonianpseudoplastic fluids show a time-dependent change inviscosity; the longer the fluid undergoesshear 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 asketchup, and are calledpseudoplastic fluids. Others such asyogurt take much longer and can become nearly solid. Many gels andcolloids 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.[2]

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 calledrheopectic. Anti-thixotropic fluids are less well documented than thixotropic fluids.[2]

History

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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 aqueousFe2O3 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.[3]

Natural examples

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Quicksand on the shore of theRiver Thames. Quicksand demonstrates thixotropy in the form ofshear thinning, in that it is solid when at rest, but quickly liquefies when agitated.

Someclays are thixotropic, influenced by thermochemical treatment, and their behaviour is of great importance instructural andgeotechnical engineering.[4][5]Landslides, such as those common in thecliffs aroundLyme Regis,Dorset and in theAberfan spoil tip disaster inWales are evidence of this phenomenon. Similarly, alahar is a mass of earthliquefied by avolcanic event, which rapidly solidifies once coming to rest.

Drilling muds used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions (such asheather honey ormānuka honey).

Bothcytoplasm and theground substance in the human body are thixotropic, as issemen.[6]

Some clay deposits found in the process of exploringcaves 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

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Many kinds of paints and inks—e.g.,plastisols used insilkscreentextile printing—exhibit thixotropic qualities.[7] 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 inCMYK-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.[8]

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

Solder pastes 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 liquefactionmiracles such as that ofSaint Januarius inNaples.[9]

Semi-solid casting processes such asthixomoulding use the thixotropic property of some alloys (mostlylight metals 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 normalinjection molding.

Fumed silica is commonly used as arheology agent to make otherwise low-viscous fluids thixotropic. Examples range from foods to epoxy resin in structural bonding applications likefillet joints.

Common use

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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.[10]

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.[11]

Negative effects

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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.[12] 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

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The word comes fromAncient Greek θίξιςthixis 'touch' (fromthinganein 'to touch') and-tropy,-tropous, from Ancient Greek -τρόπος-tropos 'of turning', from τρόποςtropos 'a turn', from τρέπεινtrepein, 'to turn, change'.[13][14] Hence, it can be translated as something that turns (or changes) when touched. It was invented byHerbert Freundlich originally for asol-gel transformation.[15]

See also

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References

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  1. ^Morrison, Ian (2003). "Dispersions".Kirk-Othmer encyclopedia of Chemical Technology.doi:10.1002/0471238961.0409191613151818.a01.ISBN 978-0471238966.
  2. ^abMewis, J; Wagner, N J (2009). "Thixotropy".Advances in Colloid and Interface Science.147–148:214–227.doi:10.1016/j.cis.2008.09.005.PMID 19012872.
  3. ^Mewis, Jan; Wagner, Norman J. (March 2009)."Thixotropy".Advances in Colloid and Interface Science.147–148:214–227.doi:10.1016/j.cis.2008.09.005.PMID 19012872.
  4. ^Krupskaya, V. V.; Zakusin, S. V.; Tyupina, E. A.; Dorzhieva, O. V.; Chernov, M. S.; Bychkova, Ya. V. (March 2019). "Transformation of Structure and Adsorption Properties of Montmorillonite under Thermochemical Treatment".Geochemistry International.57 (3):314–330.Bibcode:2019GeocI..57..314K.doi:10.1134/S0016702919030066.
  5. ^Ogolo, Oghenerume; Arinkoola, Akeem O.; Ngene, Peter; Ogbaga, Chukwuma C.; Osisanya, Samuel (12 November 2023)."Thermochemical Treatment of Nigerian Raw Clays for Oil and Gas Drilling Operations".ChemEngineering.7 (6): 110.doi:10.3390/chemengineering7060110.
  6. ^Hendrickson, T: "Massage for Orthopedic Conditions", page 9. Lippincott Williams & Wilkins, 2003.
  7. ^Köhler, Klaus; Simmendinger, Peter; Roelle, Wolfgang; Scholz, Wilfried; Valet, Andreas; Slongo, Mario (2010). "Paints and Coatings, 4. Pigments, Extenders, and Additives".Ullmann's Encyclopedia Of Industrial Chemistry.doi:10.1002/14356007.o18_o03.ISBN 978-3527306732.
  8. ^Wen, Pengpeng; Feng, Zhongjun; Zheng, Baicun (August 2023)."Thixotropy of fresh cement pastes in presence of cationic polymer".Construction and Building Materials.394: 132302.doi:10.1016/j.conbuildmat.2023.132302.
  9. ^Garlaschelli, L; Ramaccini, F; Della Scala, S (1994)."The Blood of St. Januarius".Chemistry in Britain.30 (2): 123.
  10. ^Ojeda-Farías, O.; Hebraud, P.; Lootens, D.; Liard, M.; Mendoza-Rangel, J.M. (July 2019)."Thixotropy of reactive suspensions: The case of cementitious materials".Construction and Building Materials.212:121–129.doi:10.1016/j.conbuildmat.2019.03.319.
  11. ^Gulraiz, Shiraz; Gray, K.E. (December 2020)."Thixotropy effects on drilling hydraulics".Journal of Natural Gas Science and Engineering.84: 103653.Bibcode:2020JNGSE..8403653G.doi:10.1016/j.jngse.2020.103653.
  12. ^Wen, Pengpeng; Feng, Zhongjun; Zheng, Baicun (August 2023)."Thixotropy of fresh cement pastes in presence of cationic polymer".Construction and Building Materials.394: 132302.doi:10.1016/j.conbuildmat.2023.132302.
  13. ^Harper, Douglas."thixotropy".Online Etymology Dictionary.
  14. ^θίξις,θιγγάνειν,τροπή,τρέπειν.Liddell, Henry George;Scott, Robert;A Greek–English Lexicon at thePerseus Project.
  15. ^Reiner, M; Scott Blair, G W (1967) in Eich, F. R., (ed)Rheology, Theory and Applications Vol 4 p 465 (Academic Press, NY)

External links

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  • The dictionary definition ofthixotropy at Wiktionary
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