Self-assembled double ladder structure formed inside carbon nanotubes by encapsulation of H₈Si₈O₁₂

Unique low-dimensional SiO₂-based nanomaterials can be encapsulated and synthesized inside the nanometer-scale one-dimensional internal spaces of carbon nanotubes (CNTs). In this study, various singlewalled CNTs (SWNTs) and double-walled CNTs (DWNTs) having different diameters are used as containers for cubic octameric H₈Si₈O₁₂ molecules. High-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR) spectroscopy, and Raman spectroscopy observations revealed that, depending on the diameter of the CNTs, two types of structures are formed inside the SWNTs and DWNTs: In the case of those CNTs having inner diameters ranging from 1.2 to 1.4 nm, a new ordered self-assembled structure composed of H₈Si_4bO₈n-4 molecules was formed through the transformation of H8Si8O12; however, in the case of CNTs having inner diameters larger than 1.7 nm, a disordered structure was formed. This behavior may indicate that strong interactions occur between the CNTs and the encapsulated H₈Si_4nO_8a-4 molecules.