. Colloid, Dispersion phase and dispersion medium Origin of study of colloid starts with Thomas Graham who observed diffusion of that a solution of sugar, urea or sodium chloride through a membrane but not glue, gelatine or gum. He called the former substances as crystalloids and the latter as colloids ( In Greek, kola as gum, eidos-like). Later it was realised that any substance can be converted into a colloid by reducing its particle size to -200nm.
Hence, colloid is a homogeneous mixture of two substances in which one substance (smaller proportion) is dispersed in another substance( large proportion). In a colloid, the substance present in larger amount is called dispersing medium and the substance present in less amount is called dispersed phase. XII U10-Surface XII U10-Surface - - - - . .
Classifications of Colloidal solution Probably the most important colloidal systems have dispersed phase as solid and the dispersion medium as liquid. If the dispersion medium considered is water, then the colloids are referred as hydrosols or aquasols. If the dispersion medium is an alcohol, the colloid is termed as alcosol, and if benzene is the dispersion medium, it is called as benzosol. One more type of classification is based on the forces acting between the dispersal phase and dispersion medium.
In lyophillic colloids definite attractive force or affinity exists between dispersion medium and dispersed phase. Examples: sols of protein and starch. They are more stable and will not get precipitated easily. They can be brought back to colloidal solution even after the precipitation by addition of the dispersion medium.
In a lyophobic colloids, no attractive force exists between the dispersed phase and dispersion medium. They are less stable and precipitated readily, but can not be produced again by just adding the dispersion medium. They themselves undergo coagulation after a span of characteristic life time. They are called irreversible sols examples: sols of gold, silver, platinum and copper.
The following table lists the types of colloids based on the physical states of dispersed phase and dispersion medium. Classification of colloids based on the physical