||It has been suggested that this article be merged with Thixotropy. (Discuss) Proposed since April 2012.|
Shear thinning is an effect where a fluid's viscosity—the measure of a fluid's resistance to flow—decreases with an increasing rate of shear stress. Another name for a shear thinning fluid is a pseudoplastic. This property is found in certain complex solutions, such as lava, ketchup, whipped cream, blood, paint, and nail polish. It is also a common property of polymer solutions and molten polymers. Pseudoplasticity can be demonstrated by the manner in which squeezing a bottle of ketchup, a Bingham plastic, causes the contents to undergo a change in viscosity. The force causes it to go from being thick like honey to flowing like water. The study of such phenomena is called rheology.
All materials that are shear thinning are thixotropic, in that they will always take a finite time to bring about the rearrangements needed in the microstructural elements that result in shear thinning.
Modern paints are examples of pseudoplastic materials. When modern paints are applied the shear created by the brush or roller will allow them to thin and wet out the surface evenly. Once applied the paints regain their higher viscosity which avoids drips and runs.
Ketchup might at first glance appear to be a shear-thinning fluid, since once stress is applied it becomes less resistant to flow. However, it is actually a Bingham plastic, since it requires a certain amount of pressure to begin flow, but once flowing acts a Newtonian fluid. (i.e., the shear stress must be higher than its yield stress)
- The Great Ketchup Mystery
- NASA - The Physics of Whipped Cream NASA April 25, 2008
- Example of Shear Thinning for Diutan Gum at XYdatasource.com
- Barnes, Howard A. (1997). "Thixotropy a review". J. Non-Newtonian Fluid Mech., 70: 3. Retrieved 2011-11-30.
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