What are suspensions and emulsions, in science?

1 Answer
Nov 24, 2017

Heterogeneous mixtures of two or more distinct phases.


Both are heterogeneous mixtures (mixtures containing two or more distinct phases - distinct meaning not soluble or miscible in all proportions within one another).

Most commonly, "suspension" relates to a mixture of solid particles in liquid, for example muddy water. However some people also call mixtures of solid particles in gas a "suspension" as well (e.g. smoke).

"Emulsion" commonly refers to a mixture of two immiscible liquids, such as oil and water (or for example, olive oil and vinegar in salad dressing).

It is common for regular suspensions and emulsions to phase separate on standing, so, given time, muddy water separates into a layer of mud with water on top. Smoke particles can plate out onto surfaces, and your vinegar/oil dressing separates into two distinct layers.

There are chemical techniques to stabilise these sorts of systems so that they separate less easily or over a longer time. Colloids are a separate class of suspension or emulsion with specific particle size range and extra stability, such that they resist separation.