Bishop, C.L.; (2009) The construction, development and application of potential simulation models to the filling of carbon nanotubes by molten salts. Doctoral thesis , UCL (University College London).

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Abstract

Inorganic nanotube structures (INTs) can be synthesised through the direct �filling of carbon nanotube templates with molten salts. The resulting structures, usually rationalised in terms of known bulk crystal structures, are shown to be contained within a general set of structures classifi�ed in terms of folded sheets of in�finite squares and hexagons. A flexible model for the carbon nanotube is employed (using a Terso� II potential), a signifi�cant development on previous work in which a rigid description was utilised. As a result, the nanotube is free to rotate, vibrate and translate within the simulation cell and analysis techniques are developed to account for this behaviour. Molecular dynamics simulations are performed using different molten salt models. These salt models are chosen so as to reflect different relative energetics of the underlying bulk crystal structures. In this context, a new model is developed and characterised in which key bulk structures have equal energies. The molten salts are observed to directly �ll the carbon nanotubes which vary in diameter. The stability of novel key structures, which are characterised as having non-circular cross sections, are rationalised with reference to elliptical carbon nanotube distortions. For small diameter carbon nanotubes a preference for square net based INTs is observed. The energy landscapes of the inorganic nanotubes, that are revealed by the molecular dynamics simulations, appear more complex than that of the carbon nanotubes themselves. The structures of larger inorganic nanotubes formed are dependent both on the nanotube diameter and the radius ratio of the ionic salt of choice. In contrast, the morphologies of small diameter inorganic nanotubes are dependent on the nanotube diameter only. A �first principles analysis of the atomistic interactions is developed to explain this novel observation. The resulting theory is consistent with the ubiquitous nature of the rock salt nanocrystallites observed in experiment.

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