gel
A gel is a disperse system that consists of at least two components. The solid component forms a spongy , three-dimensional network, the pores of which are filled with a liquid ( lyogel ) or a gas ( xerogel ). The liquid component is thereby immobilized in the solid one. If the network is highly porous and air is the stored gas, the gel is also referred to as an airgel . Both components penetrate each other completely ( bicoherent ). This definition is the most widely used; there is no generally accepted definition.
etymology
Gel , as an acronym for gelatine, was given its current meaning by Thomas Graham . Jelly , thus a thickened meat or fruit juice, comes from the French gelée , probably as the gelatin on Latin gelu back, ice '.
Building the network
A general distinction is made between secondary valence gels and main valence gels. The network of secondary valence gels is based on dipole-dipole forces , hydrogen bonds or Coulomb forces , while that of the main valence gels is based on covalent atomic bonds . Minor valence gels are heat reversible (e.g. gels based on pectin or gelatine).
The network can be formed from both organic and inorganic compounds.
Rheological properties
Gels can be described as viscoelastic fluids . Their fluid properties are thus between those of an ideal liquid and those of an ideal solid.
In rheology , a viscoelastic fluid is usually ascribed gel character if the amount of the storage modulus is greater than that of the loss modulus , i.e. H. at the gel point .
synthesis
The formation of a gel is generally referred to as gelation , and this term encompasses quite different areas. The point in the synthesis process from which one speaks of a gel is referred to as the gel point .
In the case of foods, gelling is usually brought about by the use of gelling agents .
Gel and sol can transform into one another. By peptization is from a gel, a sol and coagulation is a sol gel.
use
Gels can be used as the basis for pharmaceutical preparations, fillers for gel saddles and gel beds , hair gel for shaping a hairstyle, as well as liquid ballpoint pen ink or as decor gel for baking. Natural fats are also often gels. Gels are also used as a matrix in the separation process of gel electrophoresis . Pudding, toothpaste, and “solid” wall paint are gels.
See also
Web links
Individual evidence
- ↑ IUPAC - gel (G02600). Retrieved January 29, 2020 .
- ↑ Stefan Sepeur: Nanotechnology . Vincentz Network, 2008, ISBN 978-3-87870-333-4 ( page 27 in the Google book search).
- ↑ Hans-Dieter Dörfler: Interfaces and colloid-disperse systems: Physics and chemistry . Springer, 2002, ISBN 978-3-540-42547-2 ( page 604 in the Google book search).
- ↑ a b Óscar Lafuente Cerdá: Thermoreversible gels of isotropic and anisotropic liquids . 2005, ISBN 978-3-86537-468-4 ( page 3 in the Google book search).
- ↑ a b Kerstin Quarch: Product design on colloidal agglomerates and gels . Universität Karlsruhe, 2010, ISBN 978-3-86644-503-1 ( page 35 in the Google book search).
- ↑ Peter Kurzweil, Paul Scheipers: Chemistry: Fundamentals, structural knowledge, applications and experiments . Vieweg + Teubner, 2009, ISBN 978-3-8348-0341-2 ( page 172 in the Google book search).