Emulsion
Definition and meaning of Emulsion in chemistry.
An emulsion is a colloidal dispersion of two immiscible liquids in which one liquid (the dispersed phase) exists as tiny droplets suspended throughout the other (the continuous phase).
In more detail
Because the two liquids naturally separate to minimize interfacial area, emulsions are thermodynamically unstable but can be kinetically stabilized for long periods using an emulsifying agent, typically an amphiphilic surfactant whose hydrophilic head and hydrophobic tail lower interfacial tension and form a protective film around each droplet, preventing coalescence. Emulsions are classified by which liquid forms the continuous phase: oil-in-water (O/W), where oil droplets disperse in water, or water-in-oil (W/O), the reverse. Over time, unstabilized emulsions break down through creaming, flocculation, or coalescence as droplets rise, cluster, or merge.
Key facts
| Field | Physical Chemistry |
|---|---|
| Droplet size | ~0.1–100 micrometers |
| Common types | Oil-in-water (O/W), water-in-oil (W/O) |
| Stabilizer | Emulsifier (surfactant), e.g., lecithin, soap |
Mayonnaise is an oil-in-water emulsion: vegetable oil droplets are dispersed in a vinegar-water phase and stabilized by lecithin, a phospholipid emulsifier from egg yolk.
Frequently asked questions
How is an emulsion different from a suspension?
An emulsion disperses one liquid within another immiscible liquid, while a suspension disperses solid particles within a liquid.
Why does an emulsion eventually separate?
Emulsions are thermodynamically unstable because forming droplets increases interfacial energy; without enough emulsifier, droplets cream, flocculate, and coalesce until the two liquid layers separate.