Question

Rheogram of which type of flow does not start from the origin

• A. Plastic Flow
• B. Dilatant Flow
• C. Pseudoplastic Flow
• D. Newtonian

Hint:

Understanding flow behavior is critical in pharmaceutical formulation, especially for suspensions, emulsions, and ointments to ensure proper processing and patient compliance.

Answer 1

The Correct Option is A

A rheogram is a graph of shear stress versus shear rate used to describe the flow behavior of fluids. - Plastic flow is characterized by the presence of a yield stress that must be overcome before flow begins. This means the rheogram does not start from the origin; instead, it has a positive intercept on the shear stress axis. The fluid behaves like a solid until this yield stress is exceeded. Examples include toothpaste and ketchup.
- Dilatant flow (shear-thickening) fluids show an increase in viscosity with increasing shear rate, but their rheograms start from the origin.
- Pseudoplastic flow (shear-thinning) fluids have decreasing viscosity with increasing shear rate and also start from the origin on the rheogram.
- Newtonian fluids exhibit a linear relationship between shear stress and shear rate with zero intercept, thus their rheogram always starts from the origin.
Therefore, only plastic flow shows a rheogram that does not start from the origin due to the yield value that must be exceeded for flow to commence.