Encapsulation of TiO₂ nanoparticles into single-walled carbon nanotubes

Nanostructures such as carbon nanotubes and titanium dioxide (TiO ₂) offer the means to create novel nanoscale devices and technologies. The question as to whether or not TiO₂-nanoparticle (TiO₂-NP) can be encapsulated in a single-walled carbon nanotube (SWNT) depends on the physical and chemical interactions between the TiO ₂-NP and the SWNT. Motivated by nanoscale encapsulation research and nanoscale delivery systems, we present a simple but useful model to study the system comprised of an SWNT encapsulated with TiO₂-NP under various conditions. Using the well-known Lennard-Jones (6-12) potential for both cylindrical- and spherical-shaped TiO₂-NP, analytical expressions are obtained for calculating the potential energy, the encapsulating energy and the force distribution and other quantities. In particular, the suction force experienced by an SWNT located near an open end of a semi-infinite SWNT is considered. It is found that the calculated condition for the suction behavior depends only on the difference of their radii (b -a): cylindrical TiO ₂-NP b-a = 3.561 Å and spherical TiO₂-NP b-a = 3.304 Å. Connection with a possible drug delivery application is also discussed.