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disperse systems with a liquid or gaseous dispersion medium, having some properties of solids—the ability to preserve their shape, strength, elasticity, and plasticity. These properties of gels are due to the existence in them of a structural network (framework) formed by the disperse-phase particles, which are interconnected by molecular forces of various types.

Typical gels in the form of gelatinous precipitates (coagels) are formed from sols by coagulation or from supersaturated solutions of both low-molecular-weight and macromolecular substances by phase-separation processes. Gels with an aqueous dispersion medium are known as hydrogels; those with a hydrocarbon medium are known as organogels. The hardening of sols throughout their entire volume without the separation of a precipitate or the disturbance of their homogeneity gives so-called lyogels. The entire dispersion medium in these gels is immobilized because of mechanical occlusion within the cells of the structural network. The greater the particle asymmetry, the lower the disperse-phase content at which a gel is formed. For a hydrosol of vanadium pentoxide, 0.05 percent of the disperse phase is sufficient for the production of hardening. In other cases, a few volume percent of the disperse phase produces the same effect.

Lyogels exhibit low strength and plasticity and some elasticity and thixotropy (the ability to restore their structure after disturbance by mechanical action). Gels of soap and soaplike surface-active materials, as well as of hydroxides of many polyvalent metals, are of this type. Aerogels, or xerogels, which are microporous systems devoid of plasticity and having a brittle, irreversibly destructible structure, are produced by drying lyogels. Common sorbents are produced in this way: alumogel from aluminum hydroxide gel and silica gel from silicic-acid coagels.

Gels are frequently equated with gelatins. The latter, however, are single-phase (homogeneous) systems—true solutions of organic or inorganic polymers in low-molecular-weight liquids. In the area of chemistry and technology of synthetic resins, the infusible and insoluble solid (brittle) or semisolid (elastic-viscous plastic) products of condensation polymerization or polymerization are traditionally called gels. The three-dimensional network in these systems consists of a continuous structure of chemically bonded macromolecules.

References in periodicals archive ?
FORTESTA Gel and Testosterone Gel are controlled substances (CIII) because they contain testosterone that can be a target for people who abuse prescription medicines.
All the men in the family might use the same jar of styling gel.
Gels can also appear as arrowheads, chevrons, and V or J shapes.
Based on my work with elite cyclists and triathletes, these carbohydrate gels, when consumed at regular intervals, perform as advertised in helping eliminate hypoglycemia and the depletion of muscle glycogen.
He and his colleagues load the gel with insulin by immersing it in a solution of the hormone for 24 hours.
Ramana Tadepalli, Sales and Marketing Director of Hoefer, added, "We have always offered our customers the best gel electrophoresis equipment, but the combination of the ULTima system and the distribution agreement with Nonlinear means that Hoefer can now offer scientists even more - a high quality imaging platform complete with the leading 1D image analysis package.
Incoming QC for gels is especially important when running multi-layer film because you have more materials and extruders to check for gels.
The pores also make the gel almost as good an electrical insulator as air.
The gel formed a porous shell around each organism - trapping it, yet permitting nutrients to flow in and by-products to flow out.
They said of the TT900 S2S: "It represents a quantum jump in 2D gel image analysis.
The first studies tested Oxiplex Gel for its utility as a drug delivery system.
By utilizing our 18 years of pre-cast gel electrophoresis experience, we are able to expand our portfolio to deliver a solution to researchers looking for a higher-throughput system than our mini-gels that provides the same high quality and performance that they have come to expect," explained Amy Butler, Business Area Manager Proteomics Segment.