Alignment and Morphology Control of Ordered Mesoporous Silicas in Anodic Aluminum Oxide Channels by Electrophoretic Deposition

Reproducible alignment and complete inclusion of ordered mesoporous structures into anodic aluminum oxide (AAO) is still a challenging nanofabrication process. Hierarchical nanostructures of ordered mesoporous silica (OMS) in AAO channels were prepared directly on conducting substrates by electrophoretic deposition of colloidal silica nanoparticles in sots containing a structure directing agent. The mesoporous silica structures were found to be highly dependent on the magnitude of the applied electric field and moderately dependent on the overall deposition time. At low applied voltages, disordered porous tubules are formed. At an applied voltage of 5 V and deposition times in excess of 7 h, ordered mesoporous silicas fill the AAO channels, and the OMS pores display the onset of axial alignment with respect to the AAO pore. The deposition of the mesoporous silica structures with preferential axial alignment on conductive supports is described by a new self-assembly mechanism based on selective solvent exclusion due to confined particle packing of colloidal silica.