Talk:Thixotropy

A really nice video of a demonstration of this effect... for the reference section... can be found here: http://www.youtube.com/watch?v=f2XQ97XHjVw

Dan Greenberg Massachusetts, USA

explanation of a miracle is an Application?

"Thixotropy has been proposed as a scientific explanation of blood liquification "miracles" such as that of Saint Januarius in Naples." Really? Be it a miracle or magic, this is not an application of a thixotropy. At best it is a possible explanation, and shouldn't be an entry in the Application section of the main article (let alone the first entry). --74.179.98.160 (talk) 00:03, 13 November 2009 (UTC)

Besides, thixotropy isn't even sensible as an explanation for such phenomena. If this is to be included in the article, there should be a detailed rationale. David spector (talk) 02:38, 5 January 2010 (UTC)

Shear thinning

Is this page redundant with shear thinning? —Ben FrantzDale 23:24, 4 May 2007 (UTC)

I agree. I added a merge request to the page. ---- BAxelrod 12:27, 25 October 2007 (UTC)

I disagree: Shear thinning is related to a time-independant property of the constituve relations between shear rate and shear stress, while thixotropy is a time-dependant property. —Preceding unsigned comment added by 132.169.12.58 (talk) 14:47, 30 October 2007 (UTC)

Ditto to 132.169.12.58, above - just reading the article heads seems to make the distinction clear. In fact, a quick Googling yields this UK 'Ask a Scientist' page explicitly warning against confusion of the two. —Preceding unsigned comment added by Robin Z (talk • contribs) 17:38, 15 November 2007 (UTC)

I just had a look at shear thinning, Dilatant, Thixotropy and Rheopecty, and I think all four stubs could stand to be merged for clarity, especially as the cites on them are a cat's cradle of references to each other, with no external published source. The statements about how the four behaviors differ from each other are at present just uncited assertions. Perhaps the stubs for shear thinning and Dilatant could be merged with Non-Newtonian fluid, and the stubs for Thixotropy and Rheopecty could be merged with Rheology? -- Del C (talk) 13:11, 22 February 2008 (UTC)

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WRONG Industrially, the term "thixotropy" has nothing to do with time. The in my opinion silly use of this term in some or most of the academic literature as the hysteresis in viscosity is diametrically opposed to the industrial useage. Academics - at constant shear a change in viscosity with time - (change is often ~log(t)) Industrialists - Reduction in viscosity (shear thinning) as shear rate is increased (change is often ~log(µ)) While purists may have the idea that pseudoplasticity is synonomous with thixotropy in the industrial lexicon, they fail to understand that in both of the above cases the change is of necessity accompanied by a change in structure/orientation in the liquid which can not occur instantaneously. Hence in either case the is a relaxation time associated with the change. Also in both cases the change may or may not be reversible.

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ALSO WRONG - Ketchup is a plastic fluid, not a thixotropic fluid. I am reading: Pump Engineering Manual, by FlowServe Corporation, 1980, edited by R.E. Syska and J.R. Birk, published by ?, for copies contact: A.P. Wherry & Associates, Inc. 712 Lakewood Centre, Cleveland, Ohio 44107. On page 97 it states: "Plastic fluids have a definite 'yield value' which must be exceeded before flow will start, after which the viscosity devreases with an increase in agitation. Tomato catsup is a good example of this type of material. Once the 'yield value' has been exceeded the catsup will gush from the bottle." "Thixotropic fluids generally exhibit a dcreasing viscosity with increasing agitation, although the viscosity at any particular rate of motion may depend upon the previous agitation of the liquid. Examples are asphalts, glues, molasses, cellulose compounds, greases, paints, soaps, starches, and tars."

As an industrial chemist with many years of experience with both the literature and industrial practice (USA), I can state categorically that the industrial meaning of "thixotropy" is when viscosity is a (diminishing) function of shear with little or no consideration of time (that is, it assumes (near) instantaneous equilibrium upon application of any shear rate), while the academic definition is time dependent thinning (after change in applied shear). These are NOT the same. OTOH, it is absurd, as some here have said, that there is some meaning of the term not involving time. Only in some theoretical model can a change in applied shear occur instantaneously. In many industrial cases, the relaxation time (time to pseudo-equilibrium) is short, seconds or fractions of seconds, while in the academic literature there is not necessarily any 'final' viscosity, viscosity may continue to drop towards zero. I also dispute the definition of the term Thixotropy Index (Thixotropic Index). It is the ratio of the viscosity at two different shear rates, often differing by a factor of 10X or 100X; there is no unambiguous definition to the term 'viscosity' at zero shear rate. (We do understand that gravity is a shear force, don't we?). On a molecular level, liquids are generally all pseudoplastic, they all (with exceptions for superfluids, and fluids above their Tc) have a shear value below which shear does not cause (macroscopic) flow, but this gets into the bog/fog of molecular statistical mechanics, diffusion theory and surface effects. Viscosity is defined as the (constant) ratio of shear stress ÷ shear rate, but such a definition can fail for most liquids under many common conditions. For liquids in general, viscosity is a function of temperature, time, and shear rate - only in cases where t → ∞ and an 'equilibrium' is established can we speak about a substance having "a" ('constant') viscosity. Neither in the case of ultra-low shear rates (where molecular dynamics is dominant) nor with ultra-high shear rates (near and above the onset of (poorly understood) turbulence) is "viscosity" a meaningful, defined term.173.189.73.1 (talk) 18:21, 22 July 2014 (UTC)

Lots of good stuff but I'd differ in a couple of details. In many industrial processes, the most important time-related feature of thixotropy is the recovery time: it may indeed attain its (lower) viscosity nearly instantaneously when a high shear rate is applied, but the thixotropic property of significance may be that the viscosity stays low for a period after the high shear forces are removed, and that this period is sufficient for the desired effect to be achieved- e.g. flow and levelling for coatings. In this respect many practical industrial fluids are thixotropic, and while identifying a similar but non-time dependent property as shear thinning is of academic interest then it may be of less practical interest. (Though the food industry may be an exception to this- I don't know).

There are plenty of coating processes where a change in applied shear does indeed happen almost instantaneously, as a fluid moves from a low shear region to a high-shear region and then probably to a zero-shear region.

Gravuritas (talk) 19:31, 22 July 2014 (UTC)

Toothpaste - cite?

"Toothpaste is thixotropic, which allows it to be squeezed out of the tube, yet retain a solid shape on the brush."

I thought toothpaste was a Bingham plastic? I certainly didn't think it became more liquid the longer it was squeezed. Does anyone have a source for this? Skittle 20:53, 2 December 2007 (UTC)

I am trying to conduct research on strength parameters of soil sample "undisturbed vs remoulded". I need literature regarding this topic but unable to find - please help me - Bhim Dahal , Kathmandu —Preceding unsigned comment added by 119.2.58.142 (talk) 08:29, 3 March 2008 (UTC)

Toothpaste is certainly not thixotropic (unless you buy into the assertion elsewhere on this Talk page that widespread misuse of technical terminology in certain industries qualifies as a valid alternate definition). In general it's a Bingham plastic, although some toothpastes may very well exhibit yield-pseudoplastic behavior. I'm unsure about the paint assertion, but I'm guessing it depends upon the type of paint in question. It's entirely possible that modern paint formulations are not thixotropic, but I suspect older paints in fact are. I'm pretty sure this is all spelled out pretty clearly in Chhabra, R. P., and J.F. Richardson. Non-Newtonian Flow and Applied Rheology: Engineering Applications, Butterworth-Heinemann ©2008, or any undergraduate fluid mechanics textbook. Jelliott4 (talk) 13:08, 16 March 2011 (UTC)

Examples of rheopectic fluids?

Is a mixture of corn starch and water a rheopectic fluid? Famously, it flows when left to sit, stiffens or even shatters when poked or dropped. Monado (talk) 16:42, 21 September 2008 (UTC)

I don't know about the corn starch/water mixture, but I was wondering if the material used for "Crazy Aaron's Thinking Putty" is rheopectic. That material is largely polydimethylsiloxane, perhaps entirely PDMS excepting colorings. PDMS is thixotropic, according to the article. Anyone familiar with the material or with rheopecty? I'd be grateful for a response. Mr0t1633 (talk) 01:43, 29 January 2009 (UTC)

foot support

In the late 1960's or early 1970's there were downhill ski boots with a gel inside that was supposed to conform to the bottom of a foot over time, and this was then marketed as thixotropic. What was that gel? Was it considered a true example then of thixotropy? Is it now considered a true example? What materials are now used for auto-molding foot support?

It seems like it might be possible to obtain nearly the same funtionality with a material that was just extremely viscous, and perhaps somewhat responsive to body heat. Would there be a fancy technical term for such a material? -96.233.19.41 (talk) 21:13, 14 October 2009 (UTC)

Oar Blade Example

Re: “Pressure on the oar often results in a highly viscous (more solid) thixotropic mud on the high pressure side of the blade...”

I’m having a little trouble following this. Wouldn’t the mud on the high pressure side of the blade also experience high shear stresses in general, which would then reduce the viscosity? Am I missing something?

Psalm 119:105 (talk) 19:27, 26 June 2013 (UTC)

Emuulsion paint

Worth mentioning? The first time the word entered the public consciousness and most people's experience surely is with non-drip emulsion paint? 2.26.202.150 (talk) 09:42, 15 February 2015 (UTC)

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