Colloid and Suspension

What are colloids and suspensions?

Heterogeneous systems with 2 phases: dispersed/internal phase & dispersing/external phase

Particle size range for colloids?

1 nm to 0.5 µm

Particle size for suspensions?

> 0.5 µm

Advantages of colloids and suspensions?

Smaller volume than solutions, more stable, masks bad taste, flexible dosing, easier for some patients to swallow, depot therapy (controlled release)

Disadvantages of colloids and suspensions?

Hard to keep uniform, sedimentation & caking, difficult manufacturing, loss on storage/transport

What is flocculation?

Particles loosely aggregate into flocs; settle fast but easy to redisperse; large sedimentation volume

What is deflocculation?

Particles stay finely dispersed; settle slowly but form hard cake that’s hard to redisperse

What is controlled flocculation?

Stabilizes suspension to avoid caking while allowing easy redispersion

How do electrolytes help controlled flocculation?

Reduce electric barrier (lower zeta potential) to promote flocculation

How do surfactants help controlled flocculation?

Form polymer bridges between particles to promote loose floc formation

How do polymers help controlled flocculation?

Form protective colloids that prevent caking

Name the 3 types of flocculating agents.

Electrolytes, surfactants, polymers

In Stoke’s equation, how does particle diameter affect sedimentation?

Larger diameter = faster sedimentation

In Stoke’s equation, how does particle density affect sedimentation?

Higher density = faster sedimentation

In Stoke’s equation, how does medium density affect sedimentation?

Higher medium density = slower sedimentation

In Stoke’s equation, how does viscosity affect sedimentation?

Higher viscosity = slower sedimentation (inverse relationship)

What is wetting?

Vehicle completely contacts solute particles

How does contact angle relate to wetting?

Lower contact angle = better wetting

Name common surfactants/emulsifiers

Anionic (SLS), Cationic (Benzalkonium chloride), Amphoteric (Span, Tween), Nonionic (Lecithin [IV emulsions])

What factors affect physical stability of suspensions?

Temperature, particle aggregation, interaction with excipients