A colloid is a type of mixture where tiny particles of one substance (called the dispersed phase) are microscopically dispersed and suspended throughout another substance (called the continuous or dispersion medium). These particles are larger than molecules in a solution but small enough (approximately 1 nanometer to 1 micrometer in diameter) that they do not settle out like in suspensions and are not visible to the naked eye
. Colloids can involve different combinations of phases (solid, liquid, gas), leading to various types such as:
- Sol: solid particles dispersed in a liquid (e.g., paint, blood)
- Emulsion: liquid droplets dispersed in another liquid (e.g., milk, mayonnaise)
- Foam: gas bubbles dispersed in a liquid or solid (e.g., whipped cream, styrofoam)
- Aerosol: solid or liquid particles dispersed in a gas (e.g., fog, smoke)
- Gel: liquid dispersed in a solid network (e.g., jelly, gelatin)
Colloids often exhibit the Tyndall effect, where light is scattered by the dispersed particles, making the mixture appear translucent or opaque
. Unlike suspensions, colloidal particles remain evenly distributed and cannot be separated by simple filtration
. In summary, a colloid is a stable mixture with particles dispersed at a size scale between solutions and suspensions, resulting in unique physical properties and a wide range of natural and industrial examples
