réothixotropes

Rhéothixotropes, also called rheo-thixotropic materials, are substances that exhibit thixotropy: their apparent viscosity decreases with time under constant shear and recovers when the shear is removed. This time-dependent behavior reflects reversible changes in the material’s internal structure, such as the disruption and reformation of particle networks or polymer entanglements.

Mechanism and behavior commonly involve a breakdown of a gel-like or flocculated structure under shear, leading to a rapid drop in viscosity. If shear continues, the structure may reach a steadier, lower-viscosity state. When shear is stopped, the microstructure gradually rebuilds, and the viscosity increases again toward its original value. The rate of rebuilding depends on factors such as temperature, composition, particle interactions, and the strength of the network.

Measurement and interpretation in rheology often use controlled tests such as the three-interval thixotropy test or rheological sweeps with hysteresis. The area of the viscosity or modulus hysteresis loop between loading and unloading curves provides a quantitative measure of thixotropy; larger areas indicate stronger time-dependent structuring. Such tests help distinguish thixotropic behavior from simple shear-thinning or from rheopexy (the time-dependent increase in viscosity under shear).

Applications for rheo-thixotropic materials are widespread. They are valued in coatings and paints for ease of application that hardens after flow, in inks and pastes for controlled workability, in cosmetics, and in many food products where texture and stability depend on time-dependent structure.