Emulsions are estimated for their flow behaviour. The flow related attributes desirable for the performance of an emulsion are:
- Removal of an emulsion from a bottle or tube.
- Flow of an emulsion through a hypodermic needle.
- Spreadability of an emulsion on the skin.
- Stress induced flow changes during manufacture (milling).
Dilute emulsions possess Newtonian flow, thus the comparison of flow curves among various batches can be easily done. However, concentrated emulsions possess non-Newtonian flow, thus their analysis becomes difficult. Multipoint viscometers (like cone and plate or cup and bob type) are used for their evaluation.
A rough guide related to the type of flow obtained based on phase volume ratio is given below:
| Phase Volume Ratio | Types of Flow |
| 5% | Newtonian |
| 50% | Pseudo plastic |
| 74% | Plastic flow or phase inversion (abrupt changes in the behaviour) |
Viscosity of an optimum level is recognised for maximum physical stability. The aforementioned factors related to dispersed phase, continuous phase, and the emulsifying agent should be measured.
| Read More Topics |
| Emulsion formulation by HLB method |
| Flocculated and deflocculated suspensions |
| Interfacial properties of suspended particles |
