Difference Between Thixotropic and Rheopectic Fluids

The key difference between thixotropic and rheopectic fluids is that in thixotropic fluids, the viscosity of the fluid decreases with stress over time whereas, in rheopectic fluids, the viscosity of the fluid increases with stress over time.

Fluids are liquid or gaseous substances that have a viscosity. We can divide fluids into two types based on the viscosity as thixotropic and rheopectic fluids. However, both of these are non-Newtonian fluids. Also, these are considered as rare fluids.

1. Overview and Key Difference
2. What are Thixotropic Fluids
3. What are Rheopectic Fluids
4. Side by Side Comparison – Thixotropic vs Rheopectic Fluids in Tabular Form
5. Summary

What are Thixotropic Fluids?

Thixotropic fluids are liquids or gases whose viscosity decreases upon applying stress over a known time period. Therefore, it can be defined as a time-dependent pseudoplastic behaviour. In contrast, the behaviour of rheopectic fluids can be described as time-dependent dilatant behaviour. These fluids show a non-linear stress-strain behaviour as well. Therefore, the longer the fluid goes under shear stress, lower the viscosity of the fluid becomes. In other words, these fluids take some time to get its viscosity equilibrium when a change in shear rate is introduced.

Some common examples of thixotropic fluids include cytoplasm of cells, synovial fluid, some varieties of honey, some types of clay, solder pastes in electronics, thread-locking fluids, gelatin, xanthan gum, etc.

What are Rheopectic Fluids?

Rheopectic fluids are liquids or gases whose viscosity of the fluid increases with stress over time. The behaviour of these fluids can be described as a time-dependent dilatant behaviour. Thus, these fluids are a rare class of non-Newtonian fluids. Also, they show an increased viscosity upon agitation. That means, when the fluid is shaken, it becomes thick, or it may even solidify. Moreover, higher the shear stress, more viscous that fluid becomes. It is because the microstructure of these rheopectic fluids is constructed under continuous shearing. Therefore, it is named as shear-induced crystallization. Some common examples of rheopectic fluids include some gypsum pastes, printer ink, lubricants, etc.

What is the Difference Between Thixotropic and Rheopectic Fluids?

Fluids are liquid or gaseous substances that have a viscosity. We can divide fluids into two types based on the viscosity: thixotropic and rheopectic fluids. The key difference between thixotropic and rheopectic fluids is that in thixotropic fluids, the viscosity of the fluid decreases with stress over time whereas, in rheopectic fluids, the viscosity of the fluid increases with stress over time.

Some examples for thixotropic fluids include cytoplasm of cells, synovial fluid, some varieties of honey, some types of clay, solder pastes in electronics, thread-locking fluids, gelatin, xanthan gum, etc. Meanwhile, some common examples for rheopectic fluids include some gypsum pastes, printer ink, lubricants, etc. Furthermore, the behaviour of thixotropic fluids can be described as time-dependent pseudoplastic behaviour. However, the behaviour of rheopectic fluids can be described as time-dependent dilatant behaviour.

The following table summarizes the difference between thixotropic and rheopectic fluid.

Summary – Thixotropic vs Rheopectic Fluids

Fluids are liquid or gaseous substances which have a viscosity. We can divide fluids into two types based on the viscosity as thixotropic and rheopectic fluids. The key difference between thixotropic and rheopectic fluids is that in thixotropic fluids, the viscosity of the fluid decreases with stress over time whereas, in rheopectic fluids, the viscosity of the fluid increases with stress over time.

Reference:

1. “Non-Newtonian Fluids: Rheopectic vs. Thixotropic.” Materials, 4 Aug. 2016, Available here.
2. “Rheopecty.” Wikipedia, Wikimedia Foundation, 5 Mar. 2020, Available here.
3. “Time-Dependent Viscosity.” Wikipedia, Wikimedia Foundation, 8 Nov. 2019, Available here.