Morphology of inorganic-organic hybrid materials derived from triethoxysilylated diethylenetriamine and tetramethoxysilane

Triethoxysilylated diethylenetriamine (f-DETA) and its mixtures with tetramethoxysilane (TMOS) have been hydrolyzed and condensed to form abrasion resistant coatings for optical plastics such as bisphenol-A polycarbonate and CR39. In this paper, the influences of the pH and water concentration on the morphology of gels derived from f-DETA alone (f-DETA100) or equal weights of f-DETA and TMOS (f-DETA50TMOS50) were studied. For the f-DETA50TMOS50 system, with an equivalent ratio (r) of water to alkoxysilane (OH/SiOR) of 4.4, sol-gel reactions at pH 0-2 often led to a particulate gel structure. However, if the reaction was carried out pH 4-5, the resulting gel often had a uniform compact structure although some particulate features were found on the surface. For the f-DETA100 system at pH 0-2, as r increased from zero, the resulting f-DETA gels exhibited a morphological transition from a monolithic uniform structure, to a porous particulate structure, and then to a compact fine particulate structure. A similar transition also existed in the binary system f-DETA50TMOS50, but the particle size was much smaller and no obvious porous stage was observed. The aging time and drying rate were also important factors influencing the structure of the f-DETA/TMOS coatings.