Preparation of Helical Mesoporous Silica and Hybrid Silica Nanofibers Using Hydrogelator

Helical mesoporous silica, methylene−silica, ethane−silica, ethene−silica, octane−silica, and phenylene−silica nanofibers were successfully prepared by sol−gel polymerization using a chiral cationic gelator under a shear flow. These helical nanofibers were constructed by bundles of ultrafine nanofibers that were formed by bundles of nanotubes. The nanotubes of the smallest unit had inner helical channels with uniform inside diameters. The morphologies of the silica nanofibers were sensitive to preparation conditions. In acidic conditions, scanning electron microscopy images showed right-handed helical nanofibers. In basic conditions, rodlike mesoporous nanofibers were formed. The circular dichroism spectrum of the phenylene−silica indicated that the chirality of the gelator was transferred to the arrangement of the phenylene segment of the hybrid silica. The thermostability was so high that the morphologies of the phenylene−silica were maintained even after being calcined at 650 °C for 5 h in air.