Atomistic Study of the Encapsulation of Diamondoids Inside Carbon Nanotubes

TL;DR

This study uses molecular dynamics simulations to explore how diamondoids are encapsulated inside carbon nanotubes, revealing diameter-dependent phases, effects of functionalization, and differences from hard-sphere models.

Contribution

It provides new insights into the molecular ordering and packing of diamondoids inside nanotubes, including the impact of functionalization and size on phase formation.

Findings

Diameter-dependent chiral ordered phases observed.

Functionalization enhances molecular packing.

Differences from hard-sphere models noted for asymmetrical diamondoids.

Abstract

The encapsulation of hydrogen-terminated nanosized diamond fragments (the so-called diamondoids) into armchair single walled carbon nanotubes with diameters in the range of 1.0 up to 2.2 nm has been investigated using classical molecular dynamics simulations. Diameter dependent molecular ordered phases were found for the encapsulation of adamantane (C10H16), diamantane (C14H20), and dihydroxy diamantane (C14H20O2). The same types of chiral ordered phases (double, triple, 4- and 5-stranded helices) observed for the encapsulation of C60 molecules were also observed for diamondoids. On the other hand, some achiral phases comprising layered structures were not observed. Our results also indicate that the modification of diamantane through functionalization with hydroxyl groups can lead to an enhancement of the packing of molecules inside the nanotubes compared to nonfunctionalized compounds. Comparisons to hard-sphere models are also presented revealing differences, specially when more asymmetrical diamondoids are considered. For larger structures (adamantane tetramers) we have not observed long-range ordering for nanotubes with diameters in the range of 1.49 to 2.17 nm but only a tendency to form incomplete helical structures.