Porous silica films were obtained by a heat treatment of poly(ethyleneglyco
l)-containing gels for micro-patterning. Changes in porosity and the amount
of adsorbed water with the heat treatment temperature in the silica films
were evaluated from the refractive index of the films. The apparent refract
ive index of the silica films in an ambient atmosphere was much higher than
the intrinsic refractive index of the film due to the large amount of adso
rbed water in the films. The amount of adsorbed water in the films decrease
d with an increase in the heat treatment temperature and became almost zero
after a heat treatment at 850 degreesC. The decrease in the amount of adso
rbed water in the films was caused by the decrease in silanol groups, which
acted as the sites for water adsorption in the films. The drastic decrease
s in thickness and in porosity of the films at temperatures from 850 to 950
degreesC occurred after the disappearance of silanol groups in the films.
The densification of the films due to collapse of the pores at high tempera
tures should have resulted from the viscous flow of silica network.