Spinning of carbon nanotube fibres using the floating catalyst high temperature route: purity issues and the critical role of sulphur.

The CVD process for the spinning of carbon nanotube (CNT) fibres combines the nucleation, growth and aggregation of CNTs in the form of an aerogel with fibre spinning into a single process step. The optimisation of the process requires agility in multi-dimensional parameter space, so one tends to find parameter 'islands' where spinning is possible, while exploration tends to follow 'routes' through this space. Here, we follow two such routes, one of which drastically improves fibre purity, the other changes the nature of the nanotubes comprising the fibres from multiwall to single wall. In the first case there is only a modest enhancement of the mechanical properties, but in the second a very considerable improvement is seen. In terms of the conditions required to make fibres comprising predominately single wall CNTs, the key factor appears to be the rigorous control of the sulphur addition, in trace quantities, coupled with the availability of carbon atoms at the earliest stage after injection, typically in the range 400-500 °C. A model is presented for the role of sulphur in floating catalysts CNT synthesis.

Iron-doped Pt-TiO2 nanotubes for photo-catalytic water splitting.

In this work we report on the photo-catalytic performance of phase-pure and iron-doped anatase and rutile nanotubes, produced via a sol-gel process using pristine carbon nanotubes as templates. The encapsulated iron residues can be used to in situ dope the TiO(2) nanotubes without phase separation. The anatase and rutile nanotubes were further impregnated with platinum crystals with a uniform dispersion and an average size of approximately 2 nm. The materials showed dramatically improved activities for the photo-catalytic splitting of water compared to commercial TiO(2) with similar surface area (up to two orders of magnitudes), due to their higher illumination area, extended absorption range and reduced electron-hole recombination rate. The homogeneous dispersion of platinum nanoparticles further increased the hydrogen evolution rate for anatase nanotubes by a factor of seven in comparison to that for the pristine material, thus proving the great potential for commercial applications.

The role of sulphur in the synthesis of carbon nanotubes by chemical vapour deposition at high temperatures.

Sulphur has been recognised as a growth promoter for carbon fibres and carbon nanotubes for over 30 years. Moreover, the Fe-C-S system, in particular, has been extensively studied for more than half a century in the fields of steelmaking and cast iron. In the present work we examine the role of sulphur in the iron-catalysed growth of carbon nanotubes during the process of direct spinning of fibres from the gas phase. A detailed microstructural characterisation of the reaction products was conducted by high resolution TEM and EELS composition mapping on a dedicated FEG STEM (VG HB 501) equipped with Cs aberration correctors. Our results agree with previous works in classical metallurgy, indicating that sulphur forms a layer on the surface of the catalyst particles that plays a role in encouraging nanotube growth by surface diffusion.

Cause of neural death in neurodegenerative diseases attributable to expansion of glutamine repeats.

Neurodegenerative diseases resulting from expanded repeat sequences of glutamine residues are associated with the formation of protein aggregates in the cell nuclei of the affected neurons, but whether these are pathogenic is controversial. Recent observations indicate that the ages of onset of these diseases are exponential functions of the repeat lengths and that the probability of neural death is constant with time. The only process known to us that could give rise to such behaviour is nucleation of the aggregates.

Deterministic numerical model for treating the three elastic constants in nematic liquid-crystalline polymers.

In this paper, a deterministic model, which considers the three Frank elastic constants, is introduced. It is based on a lattice model and a director is used to represent the orientation of the liquid crystals in each cell. A tensor expression of the so-called "texture field" is deduced so that the nematic symmetry is conserved automatically. In the current model, the evolution of the director field can be viewed as a process towards the state of zero elastic torque. The model forms the basis for an improved understanding of the mesoscale structures and rheological phenomena of nematic liquid-crystalline polymers. It has been tested in its ability to reproduce the Fréedericksz transitions, and simulations of thin liquid crystalline polymer films clearly show the effect of unequal elastic constants on the director microstructure evolution.