Gel (colloid)

A soft, semisolid colloidal material in which a liquid is immobilized within a three-dimensional network of particles or polymer chains. Its structure gives it both solid-like resistance to flow and liquid-like composition.

Colloid: A mixture in which particles or droplets of one substance are dispersed through another without dissolving at the molecular level. Gels are colloidal systems whose dispersed components form or occupy a connected network.
Gelation: The process by which molecules, particles, or droplets form a connected network that immobilizes a liquid. Gelation creates the continuous structure that gives a gel its semisolid character.
Agarose gel electrophoresis: A laboratory method that separates DNA or RNA fragments as they migrate through a porous agarose gel under an electric field. Agarose gel pores make molecular size differences visible through separation.
Sol: A colloidal dispersion of solid particles in a liquid that remains able to flow. A sol flows freely, whereas gelation creates a network that resists sustained flow.
Sol-gel transition: The formation or breakdown of a connected network that changes a fluid sol into a gel or reverses that change. This transition describes how a flowing dispersion becomes a semisolid gel.
Cross-link: A bond or association connecting separate polymer chains into a larger network. Cross-links hold many polymer gels together and limit chain motion.
Gelatin: A mixture of collagen-derived proteins that forms thermoreversible gels when cooled in water. Gelatin is a familiar food gel whose network melts and reforms with temperature.
Foam: A material containing gas bubbles dispersed through a liquid or solid continuous phase. Foams contain gas as a dispersed phase, while gels characteristically immobilize liquid within a network.
Hydrogel: A water-swollen polymer network that retains its structure while absorbing large amounts of water. Hydrogels are gels whose continuous liquid phase is water.
Percolation theory: A mathematical framework for how connected pathways emerge in systems as links or occupied sites accumulate. Network formation in gelation can be understood as a percolation process.

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