Colloid

A colloid is a <a href="/facts/Mixture/tms8rbmn">mixture</a> in which one substance consisting of microscopically <a href="/facts/Dispersion_(chemistry)/HFq2QUys">dispersed</a> <a href="/facts/Insoluble/kLE9h3Jb">insoluble</a> <a href="/facts/Particle/JHKr2w6h">particles</a> is <a href="/facts/Suspension_(chemistry)/S3xp96TL">suspended</a> throughout another substance. Some definitions specify that the particles must be dispersed in a <a href="/facts/Liquid/t9GkLWzt">liquid</a>, while others extend the definition to include substances like <a href="/facts/Aerosol/X1jXFLp2">aerosols</a> and <a href="/facts/Gel/t7eStnK0">gels</a>. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word <a href="/facts/Suspension_(chemistry)/S3xp96TL">suspension</a> is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1 <a href="/facts/Nanometre/a98sjHyu">nanometre</a> to 1 <a href="/facts/Micrometre/7eDFxD2L">micrometre</a>.
Some colloids are <a href="/facts/Translucent/PRryNNW6">translucent</a> because of the <a href="/facts/Tyndall_effect/QJ9I8yeI">Tyndall effect</a>, which is the <a href="/facts/Scattering/nMou7lEH">scattering</a> of light by particles in the colloid. Other colloids may be <a href="/facts/Opacity_(optics)/l90q0sAV">opaque</a> or have a slight color.

Colloidal suspensions are the subject of <a href="/facts/Interface_and_colloid_science/I3PtFGsj">interface and colloid science</a>. This field of study began in 1845 by <a href="/facts/Francesco_Selmi/T2Jq2Ek5">Francesco Selmi</a>, who called them pseudosolutions, and expanded by <a href="/facts/Michael_Faraday/NDcc3lyt">Michael Faraday</a> and <a href="/facts/Thomas_Graham_(chemist)/RQhhKdCs">Thomas Graham</a>, who coined the term colloid in 1861.

Colloid open-in-new

Colloid