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A gel (from the Latin gelu "freezing, cold, ice" or gelatus "frozen, immobile") is colloid that is typically 99 % wt liquid, which is immoblised by surface tension between it and a macromolecular network of fibres built from a small amount of a gelating substance present.
Composition
A solid network spans the volume of a liquid medium. Both by weight and volume, gels are mostly liquid in composition and thus exhibit densities similar to liquids, however have the structural coherence of a solid. The network can be composed of a wide variety of materials, including particles, polymers and proteins.
Cationic polymers
Cationic polymers are positively charged polymers. Their positive charges prevent the formation of coiled polymers. This allows them to contribute more to viscous in their stretched state, because the stretched-out polymer takes up more space than a coiled polymer and thus resists the flow of solvent molecules around it. Cationic polymers are a main functional component of hair gel, because the positive charged polymers also bind the negatively charged amino acids on the surface of the keratin molecules in the hair. More complicated polymer formulas exist, e.g. a copolymer of vinylpyrrolidone, methacrylamide, and N-vinylimidazole.
Types of gels
Hydrogels
Hydrogel is a network of polymer chains that are water-insoluble, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are superabsorbent (they can contain over 99% water) natural or synthetic polymers. Hydrogels possess also a degree of flexibility very similar to natural tissue, due to their significant water content.
Common uses for hydrogel are
currently used as scaffolds in tissue engineering. When used as scaffolds, hydrogels may contain human cells in order to repair tissue.;
environmentally sensitive hydrogels. These hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change.;
as sustained-release delivery system;
provide absorption, desloughing and debriding capacities of necrotics and fibrotic tissue.;
hydrogels that are responsive to specific molecules, such as glucose or antigens can be used as biosensors as well as in DDS.;
In disposable diapers where they "capture" urine, or in sanitary napkins;
contact lenses (silicone hydrogels, polyacrylamides);
medical electrodes using hydrogels composed of cross linked polymers (polyethylene oxide,polyAMPS and polyvinylpyrrolidone);
Water gel explosives;
Read more at Wikipedia.org
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