Gels:-

Gels are the colloidal systems in which liquid is the dispersed phase and solid is the dispersion medium. the process is called Galatian. e.g. Gum Arabic, Gelatin, Agar etc. if the Gels reversible i.e. can be dehydrated & rehydrated are called elastic and if are irreversible i.e. can’t be rehydrated are called non-elastic gels.

Multimolecular, Macromolecular and Associated colloids:-

The most important characteristic of colloidal particles is their size. Depending upon how the different substance attain the size laying in colloidal range, colloidal particles are classified as multimolecular, macromolecular and associated colloids.

1. Mulitmolecular colloids:- when on dissolution, a large no of atoms or small molecules (size < 1nm) aggregated together to form species having size in the colloidal range, the species thus formed are called multimolecular colloids e.g. in sulphur sol thousands of S₈ molecules form colloidal particles of sulphur. These are held together by Vander Waal’s force of attraction.
2. Macromolecular colloids:- when certain substances (polymers) having big size molecules (macromolecules) with large molecular mass are dissolved in a suitable liquid, form colloidal solutions. The colloidal particles are called the macromolecular colloids. The colloidal particles are discrete molecules. e.g. starch, protein, polyethene etc. form macromolecular colloids. These are highly stable.

Associated colloids:- the substance which when dissolved in a medium at low concentrations behave as normal. Strong electrolyte but at higher concentration behave as colloidal solution due to the formation of aggregated particles are called associated colloids. The aggregated particles thus formed are called micelles. The maximum concentration above which Micelles are formed i.e. the substance behave as colloids is called critical Micellization Concentration (CMC). The formation of micelles takes place only above a particular temp called Kraft temp(T_K)