Definition
In a deflocculated suspension, the solid particles remain discrete and uniformly dispersed throughout the liquid medium.
While these suspensions may appear more uniform, they can be prone to sedimentation and caking, making it difficult to redisperse the particles upon shaking.
Preparation of Deflocculated Suspensions
a. Particle size reduction:
The solid drug is milled or micronized for proper dispersion, similar to flocculated suspensions.
b. Wetting of particles:
A wetting agent is used to reduce interfacial tension between the particles and the liquid medium.
c. Stabilization:
A stabilizing agent, such as a non-ionic surfactant or a hydrophilic polymer, is added to the mixture to prevent the particles from aggregating or settling.
This stabilizing agent forms a protective layer around the particles, promoting repulsion between them and maintaining uniform dispersion.
Stability Problems & Solutions
a. Sedimentation and caking:
Problem: Particles may settle and form a hard cake, making redispersion difficult.
Solution: Increase the viscosity of the medium with thickening agents and use stabilizing agents like surfactants to prevent caking.
b. Particle aggregation:
Problem: Deflocculated particles may aggregate, leading to non-uniform dispersion.
Solution: Use stabilizing agents (e.g., surfactants or hydrophilic polymers) to maintain particle repulsion and uniform dispersion.