COLLOIDAL GELS

COLLOIDAL GELS

The term colloidal refers to a state of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension roughly between 1 nm and 1µm, or that in a system discontinuity are found at distances of that order. It is not necessary for all three dimensions to be in the colloidal range: fibers in which only two dimensions are in this range and thin films, in which one dimension is in this range, may also be classified as colloidal. Nor is it necessary for the units of a colloidal system to be discrete: continuous network structures, the basic units of which are of colloidal dimensions also fall in this class (e.g. porous solids, gels and foams).

DEFINITION GELS:

A gel is a solin which the solid particles are meshed such that a rigid or semi-rigid mixture results.

Examples: Fruit jelly is an example of a gel. Cooked and cooled gelatin is another example of a gel. The protein molecules of gelatin crosslink to form a soid mesh which contains pockets of liquid.

TYPES OF GELS

a.     Hydro gels

Because hydro gels have a degree of flexibility similar to natural tissue, they are often used as scaffolds in tissue engineering and may contain human cells in order to repair tissue. Hydro gels consist of more than 99 percent of water and are superabsorbent. The practical uses of hydrogels include breast implants, granules for holding soil moisture in arid areas and dressings for burns and hard- to-heal wounds.

b.    Organ gels

Organogels or organic gelulators are noncrystalline, nonglassy, thermoplastic solid materials composed of a liquid organic phase entrapped in a three- dimensionally, cross-linked network. Organogels are frequently found in food processing, pharmaceuticals and cosmetics.

c.      Xerogels

Xerogels are solids formed from gels that do not suffer from shrinkage in the process. Xerogels generally retain a high degree of porosity. Rubber and gelatin are examples of xerogels.

d.    Aerogels

Aerogels are low-density materials created when the liquid component of a gel has been replaced by nitrogen or air. This results in very low density solids that are highly effective as thermal insulators. Aerogels are used as vehicles for drug prophylaxis.