Brownian motion in colloids refers to the zig-zag, random, continuous movement of colloidal particles when they are dispersed in a fluid (liquid or gas).
This effect was first observed by the botanist Robert Brown (1827) while looking at pollen grains suspended in water. Later, it was explained as being caused by the unequal collisions of fast-moving molecules of the dispersion medium with the colloidal particles.
Key Points about Brownian Motion in Colloids:
- Colloidal particles are large enough to be seen under an ultramicroscope but still small enough to be constantly bombarded by the molecules of the dispersion medium.
- These irregular molecular impacts cause colloidal particles to move randomly in a zig-zag path.
- Brownian motion is more significant in smaller particles and at higher temperatures.
- It prevents colloidal particles from settling down under gravity, thus helping in the stability of colloids.
Examples:
- Movement of dust particles in a beam of sunlight.
- Random motion of smoke particles under a microscope.
- Colloidal gold or ink showing continuous zig-zag movement in water.
In short, Brownian motion in colloids is the random, irregular movement of colloidal particles caused by collisions with molecules of the dispersion medium, which helps maintain the stability of the colloidal solution.