Rheology is the study of the flow of matter. Most important and well known is the term “viscosity”. This describes the resistance of the material against the flow, and is defined as the shear stress divided by the shear rate. External influences such as temperature, pressure and time also affect the viscosity.
Different rheology effects can occur such as Newtonian, thixotropic or pseudoplastic flow behavior, to name the most important ones. Newtonian liquids are 100% viscous, and the viscosity is independent of the shear rate. Pseudoplastic liquids show a shear thinning effect, while the viscosity depends on the shear rate but is independent of the time. Thixotropic liquids show a shear thinning effect and time-dependent recovery.