Question

Based on the rheological behavior of fluid, all of the following shows time independent property, except:

• A. Plastic
• B. Anti-thixotropic
• C. Pseudoplastic
• D. Non-newtonian

Hint:

Anti-thixotropic fluids become thicker with time under constant shear, unlike time-independent fluids like plastic and pseudoplastic, which maintain a consistent flow behavior.

Answer 1

The Correct Option is B

Anti-thixotropic fluids exhibit a time-dependent behavior, meaning their viscosity increases over time when subjected to constant shear. This is in contrast to plastic, pseudoplastic, and non-Newtonian fluids, which can exhibit time-independent properties.

Answer 2

Rheological behaviour can be split into time-independent flow (where shear stress at a given shear rate stays constant no matter how long shear is applied) and time-dependent flow (where the material's structure changes with the duration of shearing). The question asks which of these four does NOT belong in the time-independent group.

1. Plastic: A plastic (Bingham) system needs a minimum yield stress before it starts to flow, but once flowing, its shear stress versus shear rate relationship is fixed and does not depend on how long shear has been applied. This makes it a time-independent system.
2. Anti-thixotropic: Anti-thixotropic (or rheopectic) behaviour is defined by viscosity that builds up the longer a constant shear is applied, and that then takes time to fall back down once shearing stops. Because the response changes with the duration of shearing itself, this is a time-dependent, not time-independent, type of flow.
3. Pseudoplastic: A pseudoplastic (shear-thinning) fluid shows a viscosity that drops as shear rate increases, but at any fixed shear rate the viscosity settles to the same value regardless of how long shearing continues, so this behaviour is time-independent.
4. Non-newtonian: This is a broad umbrella term for any fluid whose viscosity is not constant with shear rate. It covers plastic and pseudoplastic flow among other patterns, most of which are time-independent, so as a general category it is grouped with time-independent systems in this classification.

Only anti-thixotropic flow depends on how long shear stress has been applied, setting it apart from the other three time-independent categories.

Therefore, the correct answer is Anti-thixotropic.