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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. An example of a common gel is edible gelatin. Many gels display thixotropy - they become fluid when agitated, but resolidify when resting. By replacing the liquid with gas it is possible to prepare aerogels, materials with exceptional properties including very low density, high specific surface areas, and excellent thermal insulation properties. In 2005 a sound induced gelation effect was demonstrated.
ApplicationsMany substances can form gels when a suitable thickener or gelling agent is added to their formula. This approach is common in manufacture of wide range of products, from foods to paints, adhesives. Gels are a mixture of a solid and a liquid. In fiber-optic communications, a gel resembling petroleum jelly in viscosity is used to surround a fiber, or multiple fibers, enclosed in a loose buffer tube. This gel serves to lubricate and support the fibers in the buffer tube. It also prevents water intrusion if the buffer tube is breached. Gels are also used in fiber-optics as index-matching materials. Source: from Federal Standard 1037C and from the FAA Glossary of Optical Communications Terms Gels are an important part of sol-gel chemistry, and can be used to form nanoporous solids. The classification of gels and jellies: Gels can be loosely classified along the following lines: 1 - Either inorganic or organic in nature 2 - Having water (hydrogels), or an organic solvent (organogels) as the liquid component 3 - Being either colloidal or coarse in nature (size of the particles which form the framework) 4 - As a rigid gels, elastic jellies, and thixotropic gels (these are mechanical properties)
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