Thomas Graham in 1861, during his work on diffusion found that certain substances such as gelatin, albumin, glue, etc. Diffused at very low rate and were called colloids. The colloid particles have the size in the range of 1 to 100 nm consisting of dispersed phase and dispersion medium. The dispersed phase or dispersion medium may be solid, liquid or even a gas. Depending upon the nature of dispersion medium or dispersed phase, 8 types of systems are possible except for a gas dispersed in another gas because the gases are completely miscible with each other. The substances which have strong interaction with the dispersion medium are called lyophilic colloids while those which do not pass into collpidal state readily are called lyophobic colloids. Lyophobic sols are much less stable and are irreversible .
What is the size of colloidal particles?