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Mechanical Properties

(i) Brownian movement

(a) Robert Brown, a botanist discovered in 1827that the pollen grains suspended in water do not remain at rest but move about continuously and randomly in all directions.

(b) Later on, it was observed that the colloidal particles are moving at random in a zig – zag motion. This type of motion is called Brownian movement.

(c) The molecules of the dispersion medium are constantly colloiding with the particles of the dispersed phase. It was stated by Wiener in 1863that the impacts of the dispersion medium particles are unequal, thus causing a zig-zag motion of the dispersed phase particles.

(d) The Brownian movement explains the force of gravity acting on colloidal particles. This helps in providing stability to colloidal sols by not allowing them to settle down.

(ii) Diffusion: The sol particles diffuse from higher concentration to lower concentration region. However, due to bigger size, they diffuse at a lesser speed.

(iii) Sedimentation: The colloidal particles settle down under the influence of gravity at a very slow rate. This phenomenon is used for determining the molecular mass of the macromolecules.

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