Depending upon the nature of interaction between the dispersed phase and the dispersion medium, colloids are classified in to the lyophilic colloids (solvent attracting) and lyophobic colloids (solvent repelling). If water is the dispersion medium, it is called as hydrophilic and hydrophobic colloid respectively.
Lyophilic colloids
The meaning of the word 'lyophilic' is 'liquid-loving' or 'solvent attracting'. That means, these are colloids in which there is strong interaction between the two phases. Lyophilic colloids are those dispersions in which the dispersed phase exhibits a definite affinity for the medium and as a results extensive solvation of the colloidal particles takes place. They are directly formed by mixing the two phases.Eg :- Gum, soap, starch, gelatin, rubber etc.
These sols are also called reversible sols. Because, if the dispersion medium is separated from the dispersed phase, the sol can be reconstituted by simply mixing with the dispersion medium.
These sols are also called reversible sols. Because, if the dispersion medium is separated from the dispersed phase, the sol can be reconstituted by simply mixing with the dispersion medium.
Lyophobic colloids
The word 'lyophobic' means 'liquid hating', ie, in these sols there is little or no interaction between the two phases. Lyophobic sols are those dispersions in which there is very little attraction between dispersed phase and dispersion medium, They cannot be prepared by simply mixing the two phases. Eg :- Dispersion of metals in water, colloidal hydroxides etc.
They are irreversible in nature. Because, once precipitated, they do not given back the colloidal sol by simple addition of the dispersion medium.
They are irreversible in nature. Because, once precipitated, they do not given back the colloidal sol by simple addition of the dispersion medium.
Comparison between lyophilic and lyophobic
Lyophilic colloidal particles are easily solvated. Lyophobic colloidal particles are weakly solvated. Small quantities of electrolytes have little effect but large amount may cause salting out in lyophilic sol. In Lyophobic sol small quantities of electrolytes causes precipitation. The particles cannot be readily detected in the ultra microscope in lyophilic sol. The particles are easily detected in the ultra microscope in Lyophobic sol. Particles may migrate in either direction or not at all in an electric field in lyophilic sol. In lyophobic sol particles migrate in only one direction in an electric field. In lyophilic sol surface tension is generally lower than that of dispersion medium. In lyophobic sol surface tension is almost similar to that of the dispersion medium. Lyophilic sols are reversible. Lyophobic sols are irreversible.
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