The effects of pre-aging and concentration of surface modifying agent on the microstructure and dielectric properties of SiO2 xerogel film

Surface modification is a key process for the preparation of porous SiO2 xe rogel film by ambient pressure drying. The microstructure and surface termi nal bonds which determine the properties of the film are closely related wi th the surface modification. Two kinds of pre-aged film were prepared to in vestigate the effect of wet-gel microstructure on the surface modification of film. The concentration of surface modifying agent (tetramethylchlorosil ane; TMCS) in solvent (n-hexane) was also varied. As concentration of TMCS increased, surface morphology was obtained from a two-dimensional structure to a three-dimensional network structure with pre-aged film for 1 h at 70 degreesC. This is due to the increase in methyl groups as surface terminal bonds and the suppression of condensation reaction. Variation in film thick ness, porosity, dielectric constants, and I-E characteristic according to t he TMCS concentration in n-hexane modifying solution was explained in the v iew-point of the nature of wet-gel structure. However, because of the addit ional increase in the strength of network and the effective exchange of sur face terminal -OH groups with -OSi(CH3)(3) groups even with low concentrati on of TMCS, there were no serious changes in the properties of SiO2 xerogel film pre-aged for 12 h at 70 degreesC. (C) 2000 Elsevier Science B.V. All rights reserved.