What is Sol-Gel ?

What is Sol-Gel ?

A simple way to produce silica (glass) from solution corresponds to a chemical reaction implying metal alkoxides and water in an alcoholic solvent. The first reaction is a hydrolysis which induces the substitution of OR groups linked to silicon by silanol Si-OH groups. These chemical species may react together to form Si-O-Si (siloxane) bonds which lead to the silica network formation. This phase establishes a 3D network. The liquid used as solvent to perform the different chemical reactions remains within the pores of the so formed solid network. A gel is thus obtained.

Removing the solvent located within the pores leads to a dried gel named "xerogel", a word issued from the Greek word "xeros" which means "dry". Sintering at low temperature causes a densification of the xerogel film which becomes dense.

Multifunctional sol-gel coatings

The sol-gel technique has many advantages for the development of innovative coatings:

due to the mild and relatively low temperatures involved (ambient to 250 °C), the sol-gel process is compatible with reactions of the organic chemistry. It therefore becomes possible to associate organic and inorganic species into a single material/layer to finally obtain a hybrid compound/coating with new unexpected opportunities for new innovative surfaces.

The composition of hybrid coatings may be modified with suitable chemical species to:

  • develop colors
  • improve scratch resistance
  • provide optical functions (switching, amplification etc.)
  • strengthen mechanically and chemically the surface of the substrate
  • prepare planar guiding structures
  • prepare antibacterial coatings

The technological implementation (dip-, spin-, spray-, roll-coating) is simple, inexpensive and applicable to parts of complex geometry and of different sizes, nature (metal, ceramic, glass, polymer, textile, wood ...) and/or fragility. The flexibility of the method makes it possible to obtain film thicknesses ranging generally from 1 nanometer to 20 microns.

IONICS developed a wide range of hybrid multifunctional sol-gel coatings, which are marketed under the product name “NANOXID”.