Preparation of crack-free SiO_2 films by sol-gel processes

SiO_2 sol-gel coatings tend to crack during drying. In this paper, the main aspects of the preparation of SiO_2 sols were systematically investigated, including synthesis temperature, reaction progress, reactant conversion, and particle size of the sols. Silane and polyamide acid were used to modify these sols in order to obtain crack-free organic-inorganic hybrid films.