Fabrication of helical hybrid silica bundles

Abstract

A series of C₂-symmetric bridged silsesquioxanes derived from L- and D-valine have been designed and synthesized. They were capable of forming physical gels in organic solvents such as ethanol, THF, and 1,4-dioxane. These silsesquioxanes formed helical bundles in 1,4-dioxane. With respect to the helical sense, a clear odd–even effect was found in the carbon number of the central alkylene segment. The silsesquioxanes with odd number alkylene segments derived from L-valine tended to self-assemble into right-handed helical bundles. On the contrary, those with even number alkylene segments tended to form left-handed helical bundles. Moreover, enantiomers derived from D-valine showed the opposite helical sense. The p : d ratio played an important role in the determination of helical sense. After sol–gel polycondensation under catalysts such as HCl, NaOH, and TBAF, helical hybrid silica bundles were identified in FESEM images. The helical sense of the bundles was sensitive to the catalysts and reaction conditions. Hybrid silica sponges showing both superoleophilic and superhydrophobic properties were obtained under a HCl diffusion procedure.