Energy performs work on the material. In between elastic and viscous behaviour lies the real world of most substances, which are viscoelastic materials. The rheology described on these net-pages is for slurries and emphasises the underlying chemical effects. We continue with some definitions and common terminology used in rheology. For ideal viscous materials, the rate of deformation is in proportion to the force applied.
Deformation ceases when the applied force is removed.
The apparent viscosity is constant with changing shear rates. This behaviour is typical of simple liquids such as water. A thixotropic material becomes more fluid with increasing time of applied force. The applied force could be stirring, pumping or shaking. This effect is often reversible, so that if left undisturbed for some time a thixotropic slurry regains its viscosity.