Viscosity and thixotropy: understanding how a gel flows
Viscosity describes resistance to flow under specified conditions. Thixotropy is a time-dependent change: a material becomes less viscous during shearing and recovers its structure during rest. A gel feeling thick in a jar does not, by itself, establish thixotropy. [1][2]
KEY TAKEAWAYS
A property measured under conditions
The instrument manufacturer Anton Paar defines shear viscosity using shear stress and shear rate. For a simple Newtonian liquid, viscosity is independent of shear rate at a fixed temperature. Other materials can have different apparent viscosities under different shear conditions. “Thick” is therefore an observation, not a full measurement specification. [1]
Shear thinning versus thixotropy
Shear thinning means viscosity decreases as shear rate increases. Thixotropy adds time and recovery: the structure changes during loading and returns during rest. Anton Paar’s explanation stresses that measuring thinning alone does not fully characterise thixotropy. [2]
What to look for in a rheology report
For viscosity, look for temperature, method, shear rate or stress, and units. For thixotropy, also look for loading duration, a recovery interval and the recovery quantity reported. Anton Paar explains why a simple ratio of viscosities at two speeds does not establish structural recovery. Compare the same method and conditions rather than ranking gels by “thick” or “self-levelling” alone. [1][2]
Article Sources
- Anton Paar — Basics of rheology
Manufacturer material
Definition of viscosity and flow-behaviour passages: Newtonian and shear-thinning behaviour, including temperature and shear conditions.
- Anton Paar — Basics of thixotropy
Manufacturer material
Definition and structural-recovery passages: recovery during rest. Comparisons require the same test method and conditions.
Written and reviewed with AI assistance using the linked sources. No hands-on product testing or independent specialist review was performed.
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