My+Assignments+and+Activities+1

My assignments and activities 1 SH

__Assignment(10/8/10)__ (Here are the definitions for the rheology terms that i searched online,you're welcome to edit it...) What is means by **pseudoplastic**? 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... 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.



The distinction between a thixotropic fluid and a shear thinning fluid:
 * Thixotropy-** the property of certain gels or fluids that are thick (viscous) under normal conditions, but flow (become thin, less viscous) over time when shaken, agitated, or otherwise stressed. 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. However, this is not a universal definition; the term is sometimes applied to pseudoplastic fluids without a viscosity/time component. Many gels and colloids are thixotropic materials, exhibiting a stable form at rest but becoming fluid when agitated.
 * ~**A thixotropic fluid displays a decrease in viscosity over time at a constant rate.
 * ~**A shear thinning fluid displays decreasing viscosity with increasing shear rate.

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.
 * Shear thinning** - 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, and whipped cream. 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.