Shear thinning

Shear thinning is an effect where viscosity decreases with increasing rate of shear stress. Materials that exhibit shear thinning are called 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 shaking a bottle of ketchup causes the contents to undergo an unpredictable change in viscosity. The force causes it to go from being thick like honey to flowing like water.

Unlike a thixotropic fluid, shear thinning fluid viscosity decreases with increasing shear rate, while thixotropic fluid viscosity decreases over time at a constant shear rate.

Everyday examples

Ketchup and modern paints are examples of pseudoplastic materials, although they are often mis-labeled as being thixotropic. When shaken or squeezed out of a bottle, ketchup will thin and flow readily but will retain its shape on a burger or plate. 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.

External links

• The Great Ketchup Mystery
• NASA - The Physics of Whipped Cream NASA April 25, 2008
• Example of Shear Thinning for Diutan Gum at XYdatasource.com]

See also

• Non-Newtonian fluid
• Power-law fluid
• Dilatant
• Rheology
• Kaye effect
• Thixotropy

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