LAUSR

Abstract Pluronic-surfactant-templated silica and organosilica nanotubes, silica nanotube bundles and silicas with small ordered domains of cylindrical mesopores were characterized by using tilt-series transmission electron microscopy (TEM). In as-synthesized nanotube samples, three-dimensional (3-D) arrangements of long nanotubes, likely involving local cross-linking of nanotube pairs, were uncovered. As-synthesized silica nanotubes tended to be unstable during TEM observation, which appeared to stem from stretching and breaking of nanotubes whose parts belonged to two different nanotube aggregates, the latter undergoing shrinkage under TEM conditions. However, silica nanotubes hydrothermally treated at a sufficiently high temperature and methylene-bridged organosilica nanotubes did not undergo this kind of changes to any appreciable extent. Despite the observed instability of as-synthesized nanotubes, the calcined sample exhibited narrow pore size distribution, suggesting that if a similar degradation occurs during drying and calcination, it may merely fragment the nanotubes. Nanotube bundles were observed to exhibit 3-D structures with often curved bundle segments locally meeting one another and potentially forming loops. A junction within a seemingly continuous nanotube bundle was observed, where ends of two groups of nanotubes met. This feature is likely to have its counterparts in particles of materials with much larger ordered domain sizes. The imaging of a large-pore silica with 2-D hexagonal domains of small size revealed the presence of an impurity consisting of spheres encircled by nanotubes. These results demonstrate that the tilt-series TEM imaging is a powerful method for characterization of not only complicated 3-D morphologies of surfactant-templated materials, but also their softness and possible degradation modes.