Preparation of colloidal solutions

Preparation of colloidal solutions

Lyophilic and association colloids are formed spontaneously by simple mixing of the dispersed-phase ingredients with the dispersion medium.

The preparative methods of hydrophobic colloids may be divided into methods that involve the breakdown of larger particles into colloidal dimensions (dispersion method) and that in which the colloidal particles are formed by the aggregation of smaller particles, such as molecules (con-densation methods).

·           Dispersion methods involve the reduction of particle size of coarse particles by input of energy, which can be done using ultrasonic meth-ods, electrical methods, or shearing.

·           Condensation methods involve the aggregation of subcolloidal-sized dispersed phase into colloidal particles, which usually involves super-saturation of the dispersed-phase concentration, followed by spontane-ous formation and growth of dispersed-phase nuclei. Supersaturation may be brought about by the addition of solute, change in solvent, or reduction in temperature. For example, if sulfur is dissolved in alcohol and the concentrated solution is then poured into an excess of water, many small nuclei form in the supersaturated solution. They grow rapidly to form a colloidal solution.

Other condensation methods involve a chemical reaction, such as reduction, oxidation, or hydrolysis. For example, colloidal sulfur may be obtained by passing hydrogen sulfide through a solution of sulfur dioxide.