Some other inks, such as those used in CMYK-type process printing, are designed to regain viscosity even faster, once they are applied, in order to protect the structure of the dots for accurate color reproduction. In many cases it is desirable for the fluid to flow sufficiently to form a uniform layer, then to resist further flow, thereby preventing sagging on a vertical surface. Many kinds of paints and inks-e.g., plastisols used in silkscreen textile printing-exhibit thixotropic qualities. (i.e., fluid velocity is not linearly proportional to the square root of the pressure differential over the oar blade). Flow from the high pressure side to the low pressure side of the oar blade is non-Newtonian. 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. These clays were deposited in the past by low-velocity streams which tend to deposit fine-grained sediment.Ī thixotropic fluid is best visualised by an oar blade embedded in mud. 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. Honey from honey bees may also exhibit this property under certain conditions (such as heather honey or manuka honey).īoth cytoplasm and the ground substance in the human body are thixotropic, as is semen. Similarly, a lahar is a mass of earth liquefied by a volcanic event, which rapidly solidifies once coming to rest.ĭrilling muds used in geotechnical applications can be thixotropic. 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. Some clays are thixotropic, with their behavior of great importance in structural and geotechnical engineering. Quicksand demonstrates thixotropy in the form of shear thinning, in that it is solid when at rest, but quickly liquefies when agitated. Quicksand on the shore of the River Thames. JSTOR ( April 2022) ( Learn how and when to remove this template message).Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources in this section. This section needs additional citations for verification. Anti-thixotropic fluids are less well documented than thixotropic fluids. Fluids which exhibit this property are sometimes called rheopectic. Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. An overview of thixotropy has been provided by Mewis and Wagner. Thixotropy arises because particles or structured solutes require time to organize. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated. Others such as yogurt take much longer and can become nearly solid. Some thixotropic fluids return to a gel state almost instantly, such as ketchup, and are called pseudoplastic fluids. A thixotropic fluid is a fluid which takes a finite time to attain equilibrium viscosity when introduced to a steep change in shear rate. Some non-Newtonian pseudoplastic fluids show a time-dependent change in viscosity the longer the fluid undergoes shear stress, the lower its viscosity. They then take a fixed time to return to a more viscous state. Certain gels or fluids that are thick or viscous under static conditions will flow (become thinner, less viscous) over time when shaken, agitated, shear-stressed, or otherwise stressed ( time-dependent viscosity). Thixotropy is a time-dependent shear thinning property. Change in viscosity of a gel or fluid caused by stress Manuka honey is an example of a thixotropic material.
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