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Thixotropy is a time-dependent shear thinning property. Certain gels or fluids that are thick (viscous) under static conditions will flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed (time dependent viscosity). They then take a fixed time to return to a more viscous state. In more technical language: some non-Newtonian pseudoplastic fluids show a time-dependent 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. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. Others such as yogurt take much longer and can become nearly solid. Many gels and colloids 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. Fluids which exhibit this property are usually called rheopectic. They are much less common. ==Natural examples== Some clays are thixotropic, with their behavior of great importance in structural and geotechnical engineering. Landslides, such as those common in the cliffs around Lyme Regis, Dorset and in the Aberfan spoil tip disaster in Wales are evidence of this phenomenon. Similarly, a lahar is a mass of earth liquefied by a volcanic event, which rapidly solidifies once coming to rest. Drilling muds used in geotechnical applications can be thixotropic. Honey from honey bees may also exhibit this property under certain conditions (such as heather honey or mānuka honey). Another example of a thixotropic fluid is the synovial fluid found in joints between some bones. Both cytoplasm and the ground substance in the human body is thixotropic, as is semen.〔Hendrickson, T: "Massage for Orthopedic Conditions", page 9. Lippincott Williams & Wilkins, 2003.〕 Some clay deposits found in the process of exploring caves exhibit thixotropism: an initially solid-seeming mudbank will turn soupy and yield up moisture when dug into or otherwise disturbed. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment. A thixotropic fluid is best visualised by an oar blade embedded in mud. Pressure on the oar often results in a highly viscous (more solid) thixotropic mud on the high pressure side of the blade, and low viscosity (very fluid) thixotropic mud on the low pressure side of the oar blade. Flow from the high pressure side to the low pressure side of the oar blade is non-Newtonian. (i.e.: fluid velocity is not proportional to the square root of the pressure differential over the oar blade). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thixotropy」の詳細全文を読む スポンサード リンク
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