The Sol-Gel process allows the easy synthesis of ceramic and glass materials with high

purities and homogeneities by using preparation techniques different from the traditional process

of fusion of oxides. This process occurs in liquid solutions in the presence of organometallic

precursors such as metal alkoxides (tetramethoxysilane, tetraethoxysilane, Zr(IV)-propoxide, or

Ti(IV)-butoxide), which, through acid- or base-catalyzed hydrolysis and condensation reactions

as shown in Figure 1-7, leads to the formation of a new phase (Sol).60

 M-O-R + H20 -- M-OH + R-OH (Hydrolysis)

 M-OH + HO-M -- M-O-M + H20 (Water condensation)

 M-O-R + HO-M M-O-M + R-OH (Alcohol condensation)

 ( M = S i, Z r, T i)

Figure 1-7. Sol-Gel hydrolysis and condensation reactions.

 The Sol is made of solid particles of a diameter of a few hundred nanometers suspended in

a liquid phase. The particles then condense in a new phase (Gel) in which a solid macromolecule

is immersed in a liquid phase (solvent). Drying the Gel by means of low temperature treatments

allows the formation of materials in a wide variety of forms: ultra-fine or spherical shaped

powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic

ceramics and glasses, or extremely porous aerogel materials as illustrated in Figure 1-8.61 Sol-Gel

materials can be used for instance in chemical sensing,62 drug delivery,63 Or electrochromics.64

As further explained in Chapter 6, the formation of a rigid shell to impart stability to the

microemulsion droplets resulting in the formation of core-shell nanocapsules was done by

polycondensation of tetramethoxysilane directly on the microemulsion droplet surface previously

functionalized with trimethoxysilane groups. A similar polycondensation method was also used

as presented in details in Chapter 5 to cross-link in two dimensions block copolymers containing

triethoxysilane-functionalized polybutadiene segments at the A/W interface.