PHYSICAL PROPERTIES OF COLLOIDS
Colloidal solutions are invariably coloured.The colour of the sol depends on the wave-length of the light scattered by the dispersed particles. The wavelenght of scattered light depends on the size and shape of colloidal particles. Thus sulphur sol with different particle size, shows different colours either bright yellow or pale yellow.
A colloidal solution is a heterogeneous mixture consisting of the particles of the dispersed phase and the dispersion medium. The colloidal particles cannot be seen with the help of an ordinary microscope but they can be seen under the ultra-microscope.
The colloidal particles can easily pass through an ordinary filter paper, ultra filters are used for the separation of colloidal particles.
The colloidal particles have a very little ability to diffuse because of their large size as compared to the solute particles present in the solution.
(v) SURFACE TENSION AND VISCOSITY
The surface tension and viscosity of sols depend on their nature. For lyophobic sol, the surface tension and viscosity are not very much different from that of the medium because of very little interaction between colloidal particles and the molecules of the medium. On the other hand lyophilic sols show variation in these properties because of the presence of interactions. Thus the viscosity of the lyophilic sols is much higher than the medium but the surface tension is generally lower than that of the pure medium.