Reminders on gel formation

Aerogels. Fundamentals

Figure 1 - Density variation according to observation scale

Figure 2 - Charge-pH diagram defining the aquo, hydroxo and oxo domains of a cation with charge z&#43; (after [14])

Figure 3 - Schematic representation of the relative speeds V of hydrolysis and condensation

Figure 4 - Influence of hydrolysis step duration thydro on reduced gel setting time tg reduced

Figure 5 - Silica aerogel of very low density (d &#61; 0.003) synthesized by a double-catalysis process

Figure 6 - Procedure for synthesizing a metal oxide aerogel Pb(Zr0.53Ti0.47)O3

Figure 7 - Three-dimensional divinylbenzene network

Figure 8 - Evolution of the liquid-vapor interface in the early stages of drying

Figure 9 - Radius of curvature of the liquid-vapour separation surface

Figure 10 - Variation in the height of a silica gel subjected to temperature cycling

Figure 11 - Phase diagram of a compound in the liquid state at room temperature

Figure 12 - (p, T) diagram of the critical line of a methanol-water mixture

Figure 13 - Phase diagram (p, T) representing the superenvelope tangent to all envelopes of the phases (p, T, x) of the CO2/ethanol mixture.

Figure 14 - Schematic diagram of supercritical drying equipment

Figure 15 - Possible aerogel routes

Figure 16 - Evolution of the liquid-vapor meniscus following autoclave filling during temperature rise

Figure 17 - Appearance of crack network when drying too quickly

Figure 19 - Aerogel photos

Figure 20 - Nitrogen adsorption curve from which specific surface area is calculated

Figure 21 - Evolution of the volume adsorbed by an aerogel at high relative pressures

Figure 22 - Porous distribution of a 0.36 density aerogel

Figure 23 - Volume contraction according to the value of the imposed stress

Figure 24 - Comparison of the infrared transmission spectra of two aerogels of density 0.45, dried in the presence of methanol and CO2

Figure 25 - Raman scattering spectrum of a 0.36 density aerogel

Figure 26 - Schematic representation of a central scattering spectrum I(q) &#61; f(q) in logarithmic coordinates of a material with fractal geometry.

Figure 27 - Central neutron scattering reveals fractal geometry of acid-grown silica aerogels as a function of bulk density

Figure 28 - Central neutron scattering of basic aerogels as a function of bulk density