Shear thinning in the context of "Grease (lubricant)"

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👉 Shear thinning in the context of Grease (lubricant)

Grease is a solid or semisolid lubricant formed as a dispersion of thickening agents in a liquid lubricant. Grease generally consists of a soap emulsified with mineral or vegetable oil.

A common feature of greases is that they possess high initial viscosities, which upon the application of shear, drop to give the effect of an oil-lubricated bearing of approximately the same viscosity as the base oil used in the grease. This change in viscosity is called shear thinning. The term grease is also sometimes used to describe lubricating materials that are simply soft solids or high viscosity liquids, but these materials do not exhibit the shear-thinning properties characteristic of greases meeting the narrower definition. For example, petroleum jellies such as Vaseline are not generally classified as greases.

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Shear thinning in the context of Hemorheology

Hemorheology, also spelled haemorheology (haemo from Greek 'αἷμα, haima 'blood'; and rheology, from Greek ῥέω rhéō, 'flow' and -λoγία, -logia 'study of'), or blood rheology, is the study of flow properties of blood and its elements of plasma and cells. Proper tissue perfusion can occur only when blood's rheological properties are within certain levels. Alterations of these properties play significant roles in disease processes. Blood viscosity is determined by plasma viscosity, hematocrit (volume fraction of red blood cell, which constitute 99.9% of the cellular elements) and mechanical properties of red blood cells. Red blood cells have unique mechanical behavior, which can be discussed under the terms erythrocyte deformability and erythrocyte aggregation. Because of that, blood behaves as a non-Newtonian fluid. As such, the viscosity of blood varies with shear rate. Blood becomes less viscous at high shear rates like those experienced with increased flow such as during exercise or in peak-systole. Therefore, blood is a shear-thinning fluid. Contrarily, blood viscosity increases when shear rate goes down with increased vessel diameters or with low flow, such as downstream from an obstruction or in diastole. Blood viscosity also increases with increases in red cell aggregability.

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Shear thinning in the context of Thixotropic

Thixotropy is a time-dependent shear thinning property. 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). They then take a fixed time to return to a more viscous state.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 steep 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. Thixotropy arises because particles or structured solutes require time to organize.

Some fluids are anti-thixotropic: constant shear stress for a time causes an increase in viscosity or even solidification. Fluids which exhibit this property are sometimes called rheopectic. Anti-thixotropic fluids are less well documented than thixotropic fluids.

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Shear thinning in the context of Wallpaper paste

Wallpaper adhesive or wallpaper paste is a specific adhesive, based on modified starch, methylcellulose, or clay which is used to fix wallpaper to walls.

Wallpaper pastes have a typical shear thinning viscosity and a high wet adhesive tack. These properties are needed to slow down the penetration of the adhesive into the paper and wall, and give slow bonding speed which gives the wallpaper hanger time to line up the wallpaper correctly on the wall. The adhesive is usually sold in pouches or boxes as flakes that are mixed with water to produce the paste. It is also available ready mixed in tubs.

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