How are colloids classified on the basis of the nature of interaction between a dispersed phase and a dispersion medium ? Describe an important characteristic of each class. Which of the sols need stabilising agents for preservation ?

Explanation

The colloids solution in which the dispersed phase has great affinity to the dispersion medium is called a Lyophilic colloid or Lyophilic solution. Ex : Starch solution.
The starch paste when dissolved in hot water , with stirring , the starch solution is formed . The starch particles (dispersed phase) has great affinity to water molecules (dispersion medium ). So starch solution is a lyophilic solution or lyophilic colloid
Lyophobic colloid : The colloidal solution in which there exists not much affinity between the dispersed phase and dispersion medium , it is called a Lyopholic colloid or Lyophobic solution.
Ex : Gold solution.
Gold rods are placed in water containing alkali. Electric arc is applied between gold rods. the gold particles dissolves in water, to give gold solution.
Gold particles (dispersed phase) have not much affinity towards water (dispersion medium) . So this is a Lyophobic solution or Lyophobic colloid.
Lyophilic colloidals are much stable than lyophobic colloids . A very amount of electrolyte can precipitate the lyophobic colloids. But their precipitation can be prevented by the addition of small amounts of lyophilic colloids. This lyopilic colloids form a protecting layer around the lyophobic colloids and protect them from precipitation (coagulation). Lyophilic colloids used for this purpose are called protective colloids.
Ex : Gelatin, gum, starch sols are generally used as protective colloids.