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(Redirected from Thixotropic)
'Thixotropy' is the property of some non-newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite amount of time to attain equilibrium viscosity when introduced to a step change in shear rate. However, this is not a universal definition; the term is sometimes applied to pseudoplastic fluids without a viscosity/time component. It is important to note the distinction between thixotropic fluid and shear-thinning fluid. The former displays a decrease in viscosity 'over time at a constant shear rate', while the latter displays decreasing viscosity with 'increasing shear rate'. Fluids which exhibit the opposite property, in which shaking for a time causes solidification, are called rheopectic, sometimes called anti-thixotropic, and are much less common.
Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Modern alkyd and latex paint varieties are often thixotropic and will not run off the painter's brush, but will still spread easily and evenly, since the gel-like paint "liquefies" when brushed out. Ketchup is frequently thixotropic. Many clutch-type automatic transmissions use fluids with thixotropic properties, to engage the different clutch plates inside the transmission housing at specific pressures, which then changes the gearset.
Some clays are also thixotropic, with their behavior of great importance to structural and geotechnical engineers. In earthquake zones, clay-like ground can exhibit characteristics of liquefaction under the shaking of a tremor, greatly affecting earth structures and buildings. Similarly, a lahar is a mass of earth liquefied by a volcanic event, which rapidly solidifies once coming to a rest. Drilling muds used in geotechnical applications can be thixotropic. Landslides, such as those common in the cliffs around Lyme Regis, Dorset and in the Aberfan slag heap disaster in Wales are evidence of this phenomenon.
One example of a thixotropic fluid is Laponite, which is a mixture of water and synthetic clay. An interesting application of Laponite is its use in the lubrication of robotic snails/slugs (gastropods), which rely on Laponite's thixotropic property for locomotion.
Another example of a thixotropic fluid is the synovial fluid found in joints between some bones.
Examples of applications for thixotropic fluids are the thickening of food stuffs and medical products. Toothpaste is thixotropic, which allows it to be squeezed out of the tube, yet retain a solid shape on the brush.
The word comes from Greek ''thixis'', touch (from ''thinganein'', to touch) + ''-tropy'', ''-tropous'', from Greek ''-tropos'', of turning, from ''tropos'', changeable, from ''trepein'', to turn.
★ Aberfan
★ Dilatant (antonym)
★ Kaye effect
★ Silly putty
★ Reiner, M., and Scott Blair, Rheology terminology, in ''Rheology'', Vol. 4 pp. 461, (New York: Achedemic Press, 1967)
'Thixotropy' is the property of some non-newtonian pseudoplastic fluids to show a time-dependent change in viscosity; the longer the fluid undergoes shear, the lower its viscosity. A thixotropic fluid is a fluid which takes a finite amount of time to attain equilibrium viscosity when introduced to a step change in shear rate. However, this is not a universal definition; the term is sometimes applied to pseudoplastic fluids without a viscosity/time component. It is important to note the distinction between thixotropic fluid and shear-thinning fluid. The former displays a decrease in viscosity 'over time at a constant shear rate', while the latter displays decreasing viscosity with 'increasing shear rate'. Fluids which exhibit the opposite property, in which shaking for a time causes solidification, are called rheopectic, sometimes called anti-thixotropic, and are much less common.
| Contents |
| Examples |
| Applications |
| Etymology |
| See also |
| References |
Examples
Ketchup displays thixotropic properties.
Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Modern alkyd and latex paint varieties are often thixotropic and will not run off the painter's brush, but will still spread easily and evenly, since the gel-like paint "liquefies" when brushed out. Ketchup is frequently thixotropic. Many clutch-type automatic transmissions use fluids with thixotropic properties, to engage the different clutch plates inside the transmission housing at specific pressures, which then changes the gearset.
Some clays are also thixotropic, with their behavior of great importance to structural and geotechnical engineers. In earthquake zones, clay-like ground can exhibit characteristics of liquefaction under the shaking of a tremor, greatly affecting earth structures and buildings. Similarly, a lahar is a mass of earth liquefied by a volcanic event, which rapidly solidifies once coming to a rest. Drilling muds used in geotechnical applications can be thixotropic. Landslides, such as those common in the cliffs around Lyme Regis, Dorset and in the Aberfan slag heap disaster in Wales are evidence of this phenomenon.
One example of a thixotropic fluid is Laponite, which is a mixture of water and synthetic clay. An interesting application of Laponite is its use in the lubrication of robotic snails/slugs (gastropods), which rely on Laponite's thixotropic property for locomotion.
Another example of a thixotropic fluid is the synovial fluid found in joints between some bones.
Applications
Examples of applications for thixotropic fluids are the thickening of food stuffs and medical products. Toothpaste is thixotropic, which allows it to be squeezed out of the tube, yet retain a solid shape on the brush.
Etymology
The word comes from Greek ''thixis'', touch (from ''thinganein'', to touch) + ''-tropy'', ''-tropous'', from Greek ''-tropos'', of turning, from ''tropos'', changeable, from ''trepein'', to turn.
See also
★ Aberfan
★ Dilatant (antonym)
★ Kaye effect
★ Silly putty
References
★ Reiner, M., and Scott Blair, Rheology terminology, in ''Rheology'', Vol. 4 pp. 461, (New York: Achedemic Press, 1967)
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