Rheopecty

Rheopexy (also Antithixotropie or negative thixotropy) referred to in the rheology of a time dependence of the flow properties for non- Newtonian fluids in which the viscosity (thickness ) increases due to continuous mechanical stress, and decreases again after the end of the loading phase. The opposite behavior to rheopexy is called thixotropy.

Basics

Some non-Newtonian fluids increase at a constant shear viscosity with time. Following the suspension of the shear stress, the viscosity decreases again. Simplified, this means the liquid is rheopexic with the period during deformation always thicker. After completion of the shear viscosity decreases time-dependent again. No longer the liquid reaches its initial value, as they are called partially rheopex or partially antithixotrop.

Not to be confused with the dilatancy rheopexic behavior in which the viscosity increases with increasing shear at a constant shear stress, but then remains constant over time.

The cause of both phenomena is similar: the structure in the fluid changes under shear force to produce smaller particle interactions occur. After the shear force applied to these structural changes form more or less back quickly.

Examples

Rheopexic behavior demonstrate, among other Oxidsuspensionen, soap brines, gypsum - water suspensions with 40 % gypsum and some polymethylacrylic -water solutions.