Question

Thixotropic behavior is associated with

• A. Increase in viscosity
• B. Decrease in viscosity
• C. Solid \& Liquid behavior
• D. Sol-gel transformation

Hint:

Thixotropic gels are ideal for topical and ophthalmic formulations, ensuring ease of application and prolonged residence time.

Answer 1

The Correct Option is B

Thixotropy is a type of time-dependent non-Newtonian flow behavior in which a material’s viscosity decreases under applied shear stress and gradually recovers when the stress is removed. - In a thixotropic system, such as suspensions, gels, or colloidal dispersions, the internal structure is disrupted by shearing, resulting in a temporary reduction in viscosity.
- When the shear force is stopped, the structure rebuilds over time, and viscosity is restored.
- This behavior is useful in pharmaceutical and cosmetic formulations where ease of application (low viscosity during application) and retention at the site of action (high viscosity at rest) are required.
Incorrect options: - (a) Increase in viscosity is not typical of thixotropy; that is more characteristic of negative thixotropy (a rare phenomenon).
- (c) Solid \& Liquid behavior describes viscoelasticity, not specifically thixotropy.
- (d) Sol-gel transformation refers to a phase transition but not the time-dependent shear-thinning of thixotropy.
Hence, thixotropic behavior is best associated with a decrease in viscosity upon shearing.