Types of Colloids and Examples

Types of Colloids

• Whipped cream, soap, and lather are examples of foams, where gas is dispersed in a liquid.
• Pumice stone and rubber are examples of solid foams, where gas is dispersed in a solid.

Classification of Colloids

• Lyophobic colloids have no affinity between dispersed particles and the dispersion medium.
• Lyophilic colloids have a great affinity between dispersed particles and the dispersion medium.

Properties of Colloids

• Particle size: Colloids have particles between 0.1 µ and 0.001 µ in size.
• Visibility of particles: Colloids are invisible to the naked eye, but visible under a powerful microscope.
• Sedimentation of particles: Colloids do not settle down, but may settle under high centrifugation.
• Filtration through filter paper: No residue is formed.

Methods of Formation of Colloids

• Condensation (Association) method: Small particles collect until they reach colloidal size.
• Dispersion (Dissociation) method: Coarse particles are broken down until they reach colloidal size.

Types of Colloids

• 8 types of colloids exist, depending on the state of the dispersed particles and the dispersion medium.

Hydrophilic Sol Colloids

• Hydrophilic sol colloids have the property of setting into a rigid and elastic gel under changing conditions.

Gelation and Solation

• Gelation: The conversion of a sol to a gel by cooling.
• Solation: The conversion of a gel to a sol by heating.

Properties of Sol and Gel

• Sol: Most of the dispersion medium is in the free state, separating the gelatin particles.
• Gel: Much water is present, but is not easily withdrawn, and few molecules of water are free.

Tyndall Phenomenon

• Tyndall phenomenon: Scattering of light by colloidal particles, discovered by John Tyndall.
• The development of the ultra-microscope is based on the scattering of light by colloidal particles.