Three-dimensional structure of a sintered macroporous silica gel

Three-dimensional (3D) macroporous morphology of a silica gel, formed as a result of the phase separation parallel to the sol-gel transition, was observed in real space by laser scanning confocal microscopy. The 3D image of the silica gel skeleton that was sintered into full dense pure silica glasses clearly demonstrated that the gel skeleton is continuous and interconnected in 3D space. The interface between the gel skeleton and the macropore was characterized in terms of interfacial curvatures. It was found that a large portion of the interface is hyperbolic, which is also found in a phase-separated structure of a binary polymer mixture developed during the spinodal decomposition(SD). Comparison was made in terms of the probability densities of the interfacial curvatures between the silica gel and a polymer mixture having an identical phase volume fraction to one of the phases. Although the probability density distribution of the mean curvature, H, representing geometrical characteristics of the interface, was symmetrical about zero for the silica gel and that for the polymer mixture was asymmetrical, overall features of the interface shape were similar. This finding supports the idea that the 3D morphology of the macroporous silica gel is formed via SD.