ABSTRACTMacroporous silicate thick films were prepared by a sol-gel dip-coating
method accompanied by the phase separation using methyl-trimethoxysilane
(MTMS), nitric acid and dimethylformamide (DMF) as starting components. The
morphology of the film varied to a large extent depending on the time
elapsed after the hydrolysis until the dipping of the coating solution. On a
glass substrate, the films prepared by early dipping had inhomogeneous
submicrometer-sized pores on the surface of the film. At increased reaction
times, relatively narrow sized isolated macropores were observed and their
size gradually decreased with the increase of reaction time. On a polyester
substrate, in contrast, micrometer-sized isolated spherical gel domains were
homogeneously deposited by earlier dippings. With an increase of reaction
time, the volume fraction of the gel phase increased, then the morphology of
the coating transformed into co-continuous gel domains and macropores, and
finally inverted into the continuous gel domains with isolated macropores.
The overall morphological variation with the reaction time was explained in
terms of the phase separation and the structure freezing by the forced
gelation, both of which were induced by the evaporation of methanol during
the dipping operation.
Sol–gel phase transitions in thermoreversible gels: Onset of gelation and melting