5.2. Sol-Gel Method

Sol-gel method is a typical bottom-up method and is associated with two reactions steps, namely sol and gel. Sol represents a colloidal suspension of solid particles in a liquid phase and gel is the interconnected network formed between phases [90]. This process consists of two main reactions: hydrolysis of the metal alkoxides (Equation (1)) and condensation of the hydrolyzed intermediates (Equations (2) and (2′)) [90]:

Both are multi-steps processes and occur sequentially [90]. This method can be used in order to obtain inorganic metal oxides from organic metal alkoxides, esters, etc. and transparent films of organic-inorganic hybrid trough co-hydrolysis and polycondensation of alkyltrimethoxysilane-tetramethoxysilane mixtures [91]. The sol-gel procedure is a useful way to produce inorganic-organic hybrids [91].