Liquid dosage forms: suspensions and emulsions 3

What is cracking?

Complete coalescence of the internal phase, resulting in separation of emulsion into 2 layers

Why does cracking occur?

Due to the destruction of the mono/multilayer film at the interface between the droplet and external phase

If emulsion has cracked can it be reversed?

No once it has cracked it can’t be recovered

What are the 4 reasons as to why it cant be?

1) Incorrect selection of emulsifying agents

2) Presence of incompatible excipients

3) Temperature

4) Microbial spoilage

What occurs in a flocculated state?

Secondary interactions (van der waals forces) maintain droplets at a defined distance of seperation (within the secondary minimum)

Putting this into application of shaking what occurs?

Shaking will redisperse these droplets to form a homogenous formulation

What is creaming a result of?

Density difference between the oil and water phases; involves either sedimentation or elevation of droplets of internal phase, producing a layer of concentrated emulsion either at top or bottom of container

What is a problem with creaming?

Aesthetic problem (resulting emulsion is unsightly); upon shaking emulsion is rendered homogenous

Rate of creaming links to what equation?

Stoke’s equation

How can it be prevented?

If density difference between the 2 phases is 0 (in practice, cannot be easily achieved)

What are 2 methods with the rate of creaming can be reduced by?

• Reduce the average particle size of the disperse phase

  • Increase the viscosity of the emulsion

Phase inversion

Emulsion instability: Hydrophilic polymers

Emulsion instability: Adsorbed particles

Emulsifying agents