Answer to Question #101518 in Physical Chemistry for Abhishek

Question

Discuss the methods of preparation of lyophilic colloidal dispersions using dispersion
methods.

Answer 1

Lyophilic colloids readily form a sol by bringing them into contact or by warming those with the medium due to their strong affinity for the dispersion medium.

Mechanical dispersion method: In this method, the large particles of the material whose sol is to be prepared are broken down in a machine called colloid mill. Colloid mill consists of two heavy steel discs separated by a little gap. The can be adjusted according to the particle size desired. The two discs rotate at high speed (about 8000 revolutions per minute) in the opposite direction.

A suspension of the substance in water is added into the mill. The particles present in the suspension are grinded to form the particles of colloidal size and also get dispersed in water to form a sol.

Electrical dispersion method (Bredig’s arc method): This method is used for the preparation of sols metals such as gold, silver, platinum etc.

In this method, two electrodes of the metals whose sol is to be prepared are immersed into the dispersion medium and an electric arc is produced bas passing high voltage current. The dispersion medium is cooled by surrounding it with a freezing mixture.

Due the heat produced from electric arc , the metal starts vaporizing and the vapour condense into the cold dispersion medium to form to the particles of colloidal size on cooling.

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Ultrasonic dispersion: The sound waves of high frequency are usually called ultrasonic waves.

These waves can be produced when quartz crystal discs are connected with high frequency generator.

The application of ultrasonic waves for the preparation of colloidal solutions was first introduced bt wood and Loomis, in 1927.

Various substances like oils, mercury, sulphides and oxides of metals can be dispersed into colloidal state easily with the help of ultrasonic waves.