gelling

Gelling is the process by which a liquid, solution, or colloidal dispersion transforms into a gel—a solid-like, three-dimensional network that immobilizes much of the liquid within its structure. In a gel, the liquid phase is confined by a continuous scaffold, giving the material elastic and viscoelastic properties. The transition point where the material acquires a distinct elastic character is often called the gel point.

Gelling occurs through network formation by crosslinking of polymer chains or colloidal particles. Gels are broadly categorized as physical (or reversible) gels, formed by non-covalent interactions such as hydrogen bonds, ionic interactions, or crystalline zones; and chemical (or covalent) gels, formed by permanent crosslinks through covalent bonds. Physical gels can often re-form after disruption, while chemical gels tend to be more permanent.

Common gelling systems include natural polymers such as gelatin, agar, carrageenan, alginate, and pectin, as well as starch. Synthetic gelling polymers include polyacrylamide and polyvinyl alcohol. Examples of gel-forming triggers include cooling, changing pH, adding crosslinking ions or agents, or initiating chemical reactions.

Factors influencing gelling include concentration, molecular weight, temperature, pH, ionic strength, and the presence of crosslinkers. Rheological measurements, such as the storage modulus (G') and loss modulus (G''), help characterize gels, with a gel typically showing G' > G'' over a range of frequencies.

Applications span food science (texturizers and stabilizers), pharmaceuticals (hydrogels for drug delivery and controlled release), tissue engineering, wound care, and consumer products. Gelling behavior is central to understanding material performance in these contexts.