Highly ordered self-assembled mesostructured membranes: Porous structure and pore surface coverage

Highly ordered silica and hybrid organic-inorganic membranes have been obtained through a slow and controlled solvent evaporation in the presence of a triblock copolymer as the structure-directing agent. Crack-free mesostructured membranes of large dimensions have been prepared; The mesophase is self-organized into a periodic cubic structure, Im (3) over barm, and consists of macroscopic mesostructured domains that maintain the out-of-plane order throughout the material. After calcination at 350 degrees C the membranes remain transparent even though they break in fragments of some centimeters. Different techniques have been employed to characterize the mesoporous materials: small angle X-ray scattering (SAXS) using synchrotron radiation and transmission electron microscopy to study the porous structure, Fourier transform infrared spectroscopy (FTIR) in vacuum at different partial pressures to investigate the nature of the pore surface. SAXS analysis has been used to map the whole membrane, revealing some differences in the pore organization that can be attributed to a gradient in the evaporation rate. The infrared measurements at different partial pressures have elucidated the mechanism of water adsorption-desorption on the pore surface. The changes of the FTIR spectra with different partial pressure have demonstrated that the pore surface is covered by a layer of molecular water that is hydrogen bonded to silanol species. (C) 2007 Elsevier Inc. All rights reserved.