- Rheopecty
Rheopecty or rheopexy is the rare property of some
non-Newtonian fluid s to show a time-dependent change inviscosity ; the longer the fluid undergoesshearing force , the higher itsviscosity . Rheopectic fluids, such as somelubricant s, thicken or solidify when shaken. The opposite type of behaviour, in which fluids become less viscous the longer they undergo shear, is calledthixotropy and is much more common.Examples of rheopectic fluids include
gypsum pastes and printersink s.There is ongoing aggressive research into new ways to make and use rheopectic materials -- especially in high-income countries, such as the United States. There is great interest in possible military uses of this technology. Moreover, the high end of the
sports market has also begun to respond to it.Body armor and combat vehicle armor are key areas where efforts are being made to use rheopectic materials. Work is also being done to use these materials in other kinds of protective equipment, which is seen as potentially useful to reduce apparent impact stress in athletics,motor sports ,transportation accidents, and all forms ofparachuting . In particular,Footwear with rheopecticshock absorption is being pursued as adual-use technology that can provide better support to those who must frequently run, leap, climb, or descend.Confusion between rheopectic and dilatant fluids
An incorrect example often used to demonstrate rheopecty is
cornstarch mixed with water, which when mixed resembles a very viscous, white fluid. It is a cheap and simple demonstrator, which can be picked up by hand as a near-solid, but flows easily when not under pressure. However, cornstarch in water is actually adilatant fluid, since it does not show the time-dependent, shear-induced change required to order be labeled rheopectic. These terms are often and easily confused since the terms are rarely used; a true rheopectic fluid would when shaken be liquid at first, becoming thicker as shaking continued.
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