5. Monolithicity

The solid network of the gel obtained by supercritical drying is normally unstressed. As a result, it should retain its texture and be uncracked. However, the monolithicity of gels is not guaranteed.

Remember that there are so-called "physical gels", where the rigidity of the solid phase is ensured by weak bonds (Van der Waals or hydrogen bonds). Simple agitation causes the gel to return to solution. These gels, whose mechanical strength often depends on the nature of the solvent, cannot be kept monolithic.

Chemical gels, formed by strong covalent or ionic bonds, are suitable for producing monolithic aerogels by supercritical drying. Even in this case, the process parameters must be adapted to the texture and size of the gels.

• To obtain a monolithic aerogel with a texture close to that of the...