sol gel transition (rus. золь-гель переход) — a process of sol transformation into gel due to increasing concentration of the dispersed phase in the sol or under the influence of other external effects (cooling, changing pH, ionic strength of the solution).

Description

The dispersed phase particle size in a highly-dispersed stable colloidal solution - sol - is 10-9-10-6 m. Increasing the concentration of the dispersed phase leads to the emergence of coagulation contacts between particles and the start of structuring, i.e. gelation. The coagulation structures are characterised by low strength, determined by van der Waals forces, while the particles interact through an equivalent-thickness layer of the dispersion medium. For so-called long-range interaction between coagulation structures the interparticle force is 10-11-10-10 N/contact, and the distance between the particles is 10-8-10-7 m. These structures are characterised by complete spontaneous recovery after mechanical destruction. Further increase in the bulk concentration of the dispersed phase leads to the gradual disappearance of the ability to recover the original structure, and as the content of the dispersion medium decreases elastic and plastic properties are also lost. When the particles are fixed in a structure suitable for short-range coagulation, the strength of the coagulation contacts increases to 10-9-10-8, and the distance between the particles decreases to 10-9 m. This stage may include the emergence of atomic (point) contacts characterised by the force of 10-8-10-6 N/contact. To improve the stability of structures, control rheological properties and the process of structure formation, the strength of the contacts is controlled by means of modifying the surface of particles through adding surfactants or by creating a high-molecular organic polymer structure in the solution.

A special case of the sol-gel transition is a transition caused by the sol cooling below the crystallisation temperature of the solvent.

The solvent crystal formation leads to the displacement of the remaining liquid into the space between the crystals with a simultaneous increase in the sol concentration, which stimulates its transition into the gel state.

Authors

  • Gusev Alexander I.
  • Shlyakhtin Oleg A.

Sources

  1. Sol gel process // Chemical encyclopedia (in Russian). V. 2. — Мoscow: Sovetskaja ehnciklopedija, 1990. P. 173–174.
  2. Sol gels // Chemical encyclopedia (in Russian). V. 2. — Мoscow: Sovetskaja ehnciklopedija, 1990. P. 170. Gels // Chemical encyclopedia (in Russian). V. 1. — Мoscow: Sovetskaja ehnciklopedija, 1990. P. 513.

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