Abstract

The morphology of stacked coronene molecules encapsulated in a single-walled carbon nanotube (SWCNT) is investigated using atomistic simulation. First, the minimum energy configuration of coronene molecules in a SWCNT is sought by means of conjugate gradient (CG) minimization. Secondly, encapsulation of coronene molecules into a SWCNT existing in a coronene atmosphere is simulated by means of molecular dynamics (MD). In both of the simulations, the diameter of the SWCNT ranges from 1.35 to 1.69 nm, and the final configurations of coronene molecules within a SWCNT are examined. In a thin SWCNT, coronene molecules tilt against the radial direction of the SWCNT and slide relative to each other, whereas in a thick SWCNT, they do not tilt but rotate relative to each other. In a SWCNT of the intermediate diameter, they tilt, slide, and rotate. For the SWCNT diameter less than or equal to 1.52 nm, the mean tilt angle of the stacked coronene molecules almost linearly decreases with increasing the diameter, whereas for the diameter above 1.52 nm, it is approximately 0∘. To check the validity of the results, the MD simulations are performed changing the density of the coronene atmosphere and the length of the SWCNT; the results prove to be valid. Finally, the effects of temperature on the mean tilt angle and mean intermolecular distance of stacked coronene molecules are examined by a rather simplified simulation, which shows that both of them increase with increasing temperature.

Highlights

  • It has been almost a quarter of a century since carbon nanotubes (CNTs) were discovered by Iijima.1 Applications of CNTs extend over a wide variety of research fields

  • If the side views in these figures are observed, it is found that the tilt angles of the coronene molecules decrease with increasing the diameter of the single-walled carbon nanotube (SWCNT); the mean tilt angles of the coronene molecules shown in Figs. 4(a), 4(c), 4(e), 4(g), and 4(i) are 48.6◦, 32.2◦, 20.4◦, 1.5◦, and 1.3◦, respectively

  • The morphology of stacked coronene molecules encapsulated in a SWCNT of the diameter range of from 1.35 to 1.69 nm was addressed by means of conjugate gradient (CG) energy minimization and molecular dynamics (MD) simulation

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Summary

INTRODUCTION

It has been almost a quarter of a century since carbon nanotubes (CNTs) were discovered by Iijima. Applications of CNTs extend over a wide variety of research fields. They showed that the stability of coronene molecules in the electron beam increases by exchanging all the hydrogen atoms of the molecules with deuterium, 117113-3 Sakane, Mouri, and Shintani and for the isotope-substituted coronene molecules, measurements of the inter-molecular spacing and molecular orientation are possible Their precise analysis yielded the intermolecular distance 0.39 ± 0.03 nm and the tilt angle 10.2 ± 4.6◦, which they wrote are consistent with the results of Okazaki et al there are no descriptions about the chiralities and diameters of the SWCNTs in their paper. Chernov et al. studied coronene stacking inside SWCNTs using PL spectroscopy, and found that coronene and dicoronylene outside SWCNTs and coronene stacks encapsulated in SWCNTs have their own intrinsic PL spectral features, and these two can be discriminated by the PL spectra Their molecular mechanics calculation supported their optical observation, and predicted the most favorable configurations of coronene molecules depending on the SWCNT diameter. We will exclusively focus on how the morphology of the encapsulated coronene molecules depends on the SWCNT diameter

SIMULATION MODEL AND METHOD
CG energy minimization
Dynamic simulation of encapsulation
CONCLUDING REMARKS
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