SILANE ADSORPTION BEHAVIOR, MICROSTRUCTURE, AND PROPERTIES OF GLYCIDOXYPROPYLTRIMETHOXYSILANE-MODIFIED COLLOIDAL SILICA COATINGS

The adsorption of 3-glycidoxypropyltrimethoxysilane (GPS) onto silica colloids (20 nm diameter) suspended in an isopropanol/ water solution was studied and related to the microstructure and properties of coatin gs prepared from the suspensions. Si-29 NMR results indicate an adsorp tion limit of similar to 2.2 GPS monomer or repeat units per nm(2) of silica surface after 24 h in suspension. For coatings dried at 100 deg rees C, FTIR data show that surface silanols are further consumed as G PS is added beyond the adsorption limit in the suspension. The increas ed adsorption after drying may be related to enhanced reaction at the higher temperature and to drying-induced deposition onto the surfaces. Coating microstructures consist of randomly packed silica colloids wi th varying amounts of siloxane polymer filling the pores, depending on the amount of silane added. The critical cracking thickness of the co atings increased dramatically when the amount of silane added was suff icient to fill the porespace. Abrasion resistance of the coatings impr oved gradually with GPS content, but deteriorated when the GPS content was far in excess of that needed to fill the pores. Hardness measured by nanoindentation showed a similar trend as abrasion resistance. (C) 1998 Academic Press.