Gelation


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gelation

[jə′lā·shən]
(chemistry)
The act or process of freezing.
Formation of a gel from a sol.

Gelation

 

the transformation of a readily mobile or viscous fluid into a solid (a body without fluidity) that is elastic, plastic, and brittle. Gelation is characteristic of solutions of macromolecular compounds and of disperse colloidal systems. It is caused by the formation of a three-dimensional structural network (skeleton), which fills the entire volume of the liquid and destroys its mobility. In solutions of polymers such a network is formed from macromolecules linked by intermolecular forces or chemical bonds; in colloidal systems, it is formed from coupled particles of the dispersed phase.

Gelation may be caused by an increase or decrease in temperature, an increase in the concentration of the dissolved or dispersed material, a change in chemical composition of the system as a result of a chemical reaction between its components, or the introduction of specific reagents. Gelation is sometimes reversible— that is, when conditions change, a system may pass repeatedly from the liquid state to the solid state and vice versa. However, in the case of pro-found chemical or physical changes in a system, the process is irreversible.

Gelation is often observed and plays an important role in many natural and manufacturing processes. The liquid layer of a paint, lacquer, glue, or photographic emulsion gelates before finally drying. Gelation occurs upon the introduction of electrolytes into rubber latex, during the hardening of synthetic resins in the manufacture of plastics, during the cooling of gelatin and starch paste solutions, and during the coagulation of blood.

References in periodicals archive ?
CS based nano-particles/fibers, hydrogels and membranes have been formulated to embed bioactive moieties (hydrophilic, hydrophobic and macromolecules), due to the specific tissue targeting and, sustained/controlled release [15] Ionic gelation technique, among multiple preparation methods comprising complex coacervation, ionotropic gelation, self-assembly method through chemical modification, solvent evaporation/diffusion, and emulsion-droplet coalescence, is preferred for its convenience, relative simplicity, and the rid of organic solvents and high temperatures [16].
The results from the work have augmented Histogenics' overall characterization of the gelation properties of collagen.
Typical gelation profiles for alginate solutions in the presence of bivalent ions are shown in Figs.
Protein that shows denaturalization aggregation properties has lower gelation, foaming capacities and emulsification (Guil-Guerrero et al.
The gelation of the coating is reflected in the quadrature having a maximum value, designated point B, whereas vitrification corresponds to the point at which the amplitude has reached a small but constant value.
The microparticles of calcium alginate are generally prepared by two methods: extrusion method by dripping a solution of sodium alginate into a solution of a calcium salt, leading to the phenomenon of external ionic gelation; and the emulsification method, for internal ionic gelation of alginate in a water/oil emulsion (Figure 1c) (GOMBOTZ et al.
They do not survive the pasteurisation process but they can, however, produce heat-stable enzymes that are not inactivated in UHT processes, causing off-flavours, fat separation and early gelation formation.
However, the selectivity of the enzyme will generally create protein hydrolysates with a low degree of hydrolysis, thereby not inducing the typical bitterness of extensively hydrolysed proteins, nor destroying the functional protein properties such as gelation, water binding and foaming.
There are many techniques to carry out the microencapsulation of various compounds and microorganisms, among which there may be mentioned spray drying, extrusion, fluidized bed, simple or complex coacervation, liposomes, inclusion in complexes (Gouin, 2004), spray coating, interfacial polymerization, and ionic gelation (Thies, 1996), the latter being a developed process for immobilizing a cell, which uses an anionic polymer mainly alginate as component of the membrane, in combination with divalent ions such as calcium to induce gelation (King, 1988).
The time to gelation for these powder coatings depends on a number of factors.
The standard chemical method described by Coffman and Garcia (1977) was adopted in evaluating the least gelation concentrations of the samples.
The gelation kinetics and mechanical spectrum of the jams were determined with a Carri-med CSL 100 controlled stress rheometer (CSL100, 105847; Carri-Med Ltd, Dorking, Surrey, UK) using a temperature-regulated cone-plate device (radius 2 cm; angle 4[degrees]01'02", gap 98 um).