- Thixotropy in Formulation describes reversible gel-to-sol transitions under shear, improving dosage form handling.
- Thixotropy In Formulation is a desirable property in liquid pharmaceutical systems, which should have:
- High consistency in the container.
- Yet pour or spread easily upon use.
- Procaine benzyl penicillin (procaine penicillin) combines benzyl penicillin with the local anaesthetic procaine.
- Thixotropy enhances suspension stability by reducing sedimentation rate:
- Higher thixotropy → Lower settling rate.
- Suspensions with 40–70
- High inherent thixotropy and are shear-thinning.
Measurements of Thixotropy
- The most apparent characteristic of a thixotropic system is the presence of an area of hysteresis in a rheogram (shear stress vs. shear rate plot).
Advertisements
1. Bulges
- Detailed studies of different thixotropic materials can reveal various complex rheograms.
- Concentrated aqueous magma (gel) of bentonite (10–15
- Produces a hysteresis loop with a characteristic bulge in the up-curve.
- The crystalline plates of bentonite form a “house-of-cards-like structure”, which contributes to the swelling of magmas.
- Example: Aqueous bentonite gel (10–15
Advertisements
2. Spurs
- A spur is a sharp point of structural breakdown at low shear rate observed in the up-curve of the rheogram.
- This point is referred to as the spur value.
Advertisements
Negative Thixotropy (Antithixotropy)
- Negative thixotropy, also known as rheopecty, is the opposite behavior: a material increases in viscosity over time under constant shear and decreases when at rest.
-
Example Applications:
- Some lubricants or printer inks.
- Specialized biomedical gels.
-
Measurement:
- Similar tools (rheometers) are used, but the viscosity increases over time at a constant shear rate.
Advertisements
Thank you for reading from Firsthope's notes, don't forget to check YouTube videos!
