In macromolecular type of colloids, the dispersed

particles are themselves large molecules (usually

polymers). Since these molecules have dimensions

comparable to those of colloidal particles, their

dispersions are called macromolecular colloids. Most lyophilic sols belong to this category.

There are certain colloids which behave as normal strong electrolytes at low concentrations, but exhibit colloidal properties at higher concentrations due to the formation of aggregated particles. These are known as micelles or associated colloids. Surface active agents like soaps and synthetic detergents belong to this class.

1. Critical micelle concentration (CMC) is the lowest

concentration at which micelle formation appears. CMC increases with the total surfactant concentration. At concentration higher than CMC, they form extended parallel sheets known as lamellar micelles Which resemble biological membranes. With two molecules thick, the individual molecule is perpendicular to the sheets such that hydrophilic groups are on the outside in aqueous solution and on the inside is a non-polar medium.

2. In concentrated solution, micelles take the form of

long cylinders packed in hexagonal arrays and are called lytotropic mesomorphs.

3. In an aqueous solution (polar medium), the polar

groups point towards the periphery and the

hydrophobic hydrocarbon chains point towards the

centre forming the core of the micelle.

4. Micelles from the ionic surfactants can be formed

only above a certain temperature called the kraft

temperature.

5. They are capable of forming ions.

6. Molecules of soaps and detergents consist of

lyophilic as well as lyophobic parts which associate

together to form micelles.

7. Micelles may contain as many as 100 molecules or

more.

(i) Select incorrect statements (s) –