What is Thixotropy?
{{Wiktionary}} '''Thixotropy''' is the property of certain [[gel]]s or [[fluid]]s that are [[Viscosity|viscous]] (thick) under normal conditions, but flow (become thin, less viscous) when shaken, agitated, or otherwise stressed. In more technical language: some [[Non-Newtonian fluid]]s show a 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 step change in shear rate. Many [[gel]]s and [[colloid]]s are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Constant shear stress can be applied by shaking or mixing. They are much less common. ==Natural examples== It is a common experience walking on [[sand]] that in places it liquifies as one walks on it. This is a thixotropic response to [[pressure]]. In extremes, a [[quicksand]] may be danger to people and animals. Some [[clay]]s are thixotropic, and their behaviour is of great importance in [[structural engineering|structural]] and [[geotechnical engineering]]. [[Landslide]]s, such as those common in the [[cliff]]s around [[Lyme Regis]], [[Dorset]] and in the [[Aberfan disaster]] in [[Wales]] are evidence of this. Similarly, a [[lahar]] is a mass of earth liquefied by a [[volcano|volcanic]] event, which rapidly solidifies once coming to rest. [[Drilling mud]]s used in geotechnical applications can be thixotropic. [[Honey]] from honey bees may also exhibit this property under certain conditions.([[Heather]] honey). Another example of a thixotropic fluid is the [[synovial fluid]] found in joints between some bones.<ref>Hendrickson T. 2003. ''Massage for orthopedic conditions''. Lippincott Williams & Wilkins. p 9</ref> Some clay deposits found in the process of exploring [[caves]] exhibit thixotropism: an initially solid-seeming [[mud]]bank wi