Thixotropy



Thixotropy is the property of some colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.

It is important to note the distinction between a thixotropic fluid and a rheopectic, sometimes called anti-thixotropic, and are much less common.

Natural examples

Some clays are thixotropic, with their behavior of great importance in structural and geotechnical engineering. 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. Also honey from honey bees may exhibit this property under certain conditions.

Another example of a thixotropic fluid is the synovial fluid found in joints between some bones. The ground substance in the human body is thixotropic. [1]

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. Ketchup is frequently thixotropic.

Modern 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. 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.

Laponite, a mixture of water and synthetic clay, is used in the lubrication of robotic snails/slugs (gastropods), which rely on Laponite's thixotropic property for locomotion.

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

References

  • Reiner, M., and Scott Blair, Rheology terminology, in Rheology, Vol. 4 pp. 461, (New York: Achedemic Press, 1967)
  1. ^ Hendrickson, T: "Massage for Orthopedic Conditions", page 9. Lippincott Williams & Wilkins, 2003.
 
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