Question

Which of the following produces a bulge in the up curve of a hysteresis loop?

• A. \( \text{Procaine penicillin gel} \)
• B. \( \text{Magnesia magma} \)
• C. \( \text{Concentrated aqueous kaolin gel} \)
• D. \( \text{Concentrated aqueous bentonite gel} \)

Hint:

Think of bentonite gels as complex systems that can show both shear thinning and shear thickening depending on the concentration and shear rate.

Answer 1

The Correct Option is D

A bulge in the up curve of a hysteresis loop in rheology is characteristic of thixotropic systems that exhibit shear thickening (dilatancy) at certain shear rates before undergoing shear thinning. Concentrated aqueous bentonite gels are known to exhibit this complex rheological behavior. At low shear rates, they show shear thinning (thixotropy), but at intermediate shear rates, they can exhibit shear thickening (dilatancy), which would manifest as a bulge in the up curve of the hysteresis loop. Procaine penicillin gel, magnesia magma, and concentrated aqueous kaolin gel typically exhibit thixotropy (shear thinning with time) but not necessarily this intermediate shear thickening behavior that leads to a bulge in the hysteresis loop.