Three-dimensional observation of phase-separated siloxane sol-gel structures in confined spaces using laser scanning confocal microscopy (LSCM)

Porous methylsiloxane gels with bicontinuous structure were prepared via sol-gel method accompanying spinodal decomposition in a variety of confined geometries. The resultant porous structure in a two-dimensional mold has been examined closely utilizing the recent laser scanning confocal microscopy (LSCM). A drastic structural deformation due to preferential wetting by methylsiloxane-rich phase has lead to elongated columnar structure in the proximity of the surfaces. The area-averaged mean and Gaussian curvatures of spinodal interfaces were obtained by parallel surface method (PSM). In the vicinity of the surfaces, values of the mean curvature were slightly deviated from that of the isotropic bicontinuous structure, reflecting linearly elongated features of methylsiloxane gel skeleton perpendicular to the surfaces. When a scaled thickness of the sample D/Λ_m becomes less than unity, wetting transition occurred. Here, Λ_m means characteristic length of bicontinuous structure of bulk gel prepared in a three-dimensional free volume. In both one- and zero-dimensional molds, the porous structure was observed under SEM, revealed that the similar deformation and wetting transition occurred. The criterion for wetting transition, D/Λ_m<1, was universal in all confined spaces.