Phase transitions within filled carbon nanotubes

The existence and formation of ,,microtubules of graphitic carbon" was first reported in 1991. The hollow interior of single-walled carbon nanotubes (SWNTs) offers the possibility to fill the SWNTs with various materials. These nanocomposite materials represent a new generation of materials that can be synthesised on a bulk scale and that can potentially form the basis of diodes, single electron transistors, memory elements, and logic circuits. In the course of this proposal, the filling method from the melt would be used throughout. In all previous studies, the structures of the encapsulated materials were analysed only after cooling to room temperature and were compared to the corresponding bulk structures. The aim of this proposal is to put the focus on the encapsulated structures that exist on filling the SWNTs and the structures that form during the cooling to room temperature. A deeper understanding of the wetting dynamies will allow to plan experiments which lead to higher yields in incorporation. For future technological applications of the filled SWNT composites, an approximately quantitative filling is required. According to theory, the character of phase transitions (e. g. transition temperature, order, etc.) shows a pronounced dependence on size and dimensionality of a system. In the hollow cavity of a SWNT, correlation lengths can diverge only along the axis of the SWNT, and so the phase transitions in this quasi-one-dimensional environment may differ substantially from the phase transitions in the three-dimensional bulk phases. The filling of the SWNTs and the phase transitions of the encapsulated material will be followed in-situ with differential scanning calorimetry (DSC). lt would thus be possible to directly monitor the effect of the time given for encapsulation and gain information about the time required for maximum filling. A second goal is to freeze-in the structures that exist in the molten or other high-temperature states and characterise them at room temperature. This would be accomplished by various quenching techniques. The obtained samples would be characterised by high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and DSC. The University of Oxford hosts one of the most advanced electron microscope facilities in Europe which is capable of an imaging resolution < 0.8 A. In order to put a general focus on the topic of phase transitions, different kinds of phase transitions will be examined, including (a) liquid-solid phase transitions, (b) transitions from orientational disorder to orientational order of structural subunits, and (c) phase transitions in two-component systems with immiscibility gaps.