Rheopexy
Rheopexy (also antithixotropy or negative thixotropy ) in rheology refers to a time dependency of the flow properties in non-Newtonian fluids , in which the viscosity (viscosity) increases as a result of continuous mechanical stress and only decreases again after the end of the stress phase. The opposite behavior to rheopexy is called thixotropy .
Basics
Some non-Newtonian fluids increase in viscosity over time with constant shear . After exposure to the shear stress, the viscosity decreases again. In simple terms this means that the rheopex fluid becomes more and more viscous the longer it deforms. After the end of the shear stress, the viscosity decreases again as a function of time. If the fluid no longer reaches its initial value, it is referred to as partially rheopex or partially antithixotropic.
Rheopex behavior should not be confused with dilatance , in which the viscosity increases due to increasing shear , but then remains constant over time with constant shear stress.
The cause for both phenomena is similar: the structure in the fluid changes under the action of shear force, so that greater interactions occur between the particles. After the action of the shear force, these structural changes recede more or less quickly.
Examples
Rheopexic behavior show, among other oxide suspensions , soaps - Solen , gypsum - water suspensions with 40% gypsum and some polymethyl-water solutions.
Individual evidence
- ↑ DIN 1342-3: 2003-11, chap. 4.2.3, point b)
- ^ L. Gehm: Rheology - Practice-oriented Basics and Glossary. Vincentz Verlag, 1998, ISBN 3-87870-449-6 .