What is a colloid?

A colloid is a heterogeneous mixture where one substance with microscopic, insoluble particles is suspended throughout another substance. It consists of a dispersed phase and a continuous phase, and some types can scatter light through the Tyndall effect. Thomas Graham coined the term in 1861, building on earlier work by Francesco Selmi and Michael Faraday.

What we know

• A colloid is a mixture where one substance containing microscopically dispersed insoluble particles is suspended throughout another substance. [1, 2]
• Colloids are comprised of a dispersed phase representing the suspended particles and a continuous phase representing the suspension medium. [2]
• Some colloids appear translucent because of the Tyndall effect, which causes particles to scatter light. [2]
• The term colloid was coined in 1861 by Thomas Graham, following foundational research by Francesco Selmi and Michael Faraday. [2]

Still open

• Some definitions restrict colloids to particles dispersed specifically in a liquid, while broader definitions include substances like gels and aerosols.

Where to go next

• compared withHow does a suspension differ from a colloid?
• how it workedWhat is the Tyndall effect?
• whoWho was Thomas Graham?
• a case in pointWhat are aerosols and gels?
• the bigger pictureWhat is interface and colloid science?
• an unexpected connectionHow do hand-like mirror-image molecules relate to mixtures?While colloids describe heterogeneous microscopic dispersions, chiral chemistry explores pure and racemic homogeneous mixtures of mirror-image molecules.

Sources

• [1]colloid (Wikidata Q181780) · CC0 1.0
• [2]Colloid · CC BY-SA 4.0
• [3]Chirality (chemistry) · CC BY-SA 4.0
• [4]Suspension (chemistry) · CC BY-SA 4.0
• [5]Glossary of chemistry terms · CC BY-SA 4.0