Brownian movement was first discovered by Robert Brown, a botanist, in 1827. He observed that pollen grains in water do not remain at rest but move about continuously and randomly. This random continuous movement (Brownian motion) was observed in colloidal sol when the sol was viewed under a ultra microscope. Brownian motion in colloidal sols arises due to the impact of the molecules of the dispersion medium with the colloidal particles. It has been postulated that the impact of the molecules of dispersion medium on the colloidal particles are unequal. This leads to the zig-zag (random) motion of the colloidal particles.
This random movement decreases as the size of the particles increases because the effect of the impacts average out. When the size of the dispersed particles increases beyond the colloidal range, Brownian motion stops, and no Brownian movement is observed.
