| Dr S A Hayes |
| 96 |
IMPROVING THE TOUGHNESS OF COMPOSITES
Supervisor: Dr S A Hayes |
| Laminates produced from unidirectional composite pre-preg are well-known to be susceptible to impact damage, which produces extensive delaminations between layers with different orientation. While there are methods of reducing damage, it is still a major concern when designing composite components, and prevents full optimisation of the mechanical properties. This project will employ patterned interleaves between plies, with controlled mechanical properties, in order to dissipate the impact energy though mechanisms other than fracture. Optimum interleaf patterns will be established using modeling techniques, and the predictions of the model assessed experimentally. In this way, the toughness of the new systems will be compared with traditional composites to assess the degree of toughness control that the new approach provides. |
| 97 |
MECHANICAL PROPERTIES OF ALIGNED NANOCOMPOSITE MATERIALS
Supervisor: Dr S A Hayes |
| This project seeks to manufacture nanocomposite materials with controlled orientation of the reinforcement phase, in order to maximise the influence of the reinforcement on the mechanical properties. In conventional fibre reinforced composites, the maximum mechanical advantage is obtained when the fibres lie in the loading axis. However, with nanocomposites this is difficult to achieve. Currently nanocomposites have been shown to give significant improvement in the mechanical properties of rubbery polymers, but in glassy systems, success has been more elusive. This could be due to the misorientation of the reinforcement, meaning that it effectively acts as a flaw in the polymer, initiating the fracture process. By controlling the orientation it is hoped that such problems can be eliminated and the mechanical properties of nano-scale reinforcements fully exploited. |
| 98 |
SELF-HEALING POLYMERS AND COMPOSITES
Supervisors: Dr S A Hayes and Professor F R Jones |
| This project will continue development of recently patented self-healing technologies, which can currently enable an epoxy resin to recover 70% of pre-fracture load upon healing without the addition of new material. It is the aim to apply this technology in the field of advanced composites and also in adhesive resins. Projects are available in both of these areas depending on the applicants’ interests and experience. Typically, projects would involve the development and characterisation of new healing resins using guidelines that exist, followed by investigations into the technology to further our understanding of these novel functional resin systems and facilitate their adoption in commercial applications. |
| Professor G Ungar |
| 99 |
NEW LIQUID CRYSTAL AND POLYMER NANOSTRUCTURES FOR PHOTOVOLTAIC APPLICATIONS
Supervisors: Professor G Ungar and Dr X B Zeng |
| The objective is to produce purely organic and organic-inorganic nanocomposite materials from functionalized tree-like molecules called dendrimers. The materials would have high charge mobility and act as low-dimensional semiconductors, to be applied in photovoltaic cells, field-effect transistors etc. We find that the wedge- or cone-like dendrimer molecules assemble into supramolecular objects of different shape in a way similar to the self-assembly of viruses – e.g. tobacco mosaic virus, herpes virus (Percec et al. Nature, 1998 391 161; Hudson et al. Science 1997 278 449; Ungar et al. Science, 2003 299 1208). The shape and packing of the objects will be determined by crystallographic methods at Sheffield, and at the Diamond and ESRF synchrotrons, as well as at neutron facilities at Rutherford Lab and ILL Grenoble. Thin films would be studied by grazing incidence scattering (GISAXS), as well as by transmission electron microscopy (TEM) and atomic force microscopy (AFM). This work is in collaboration with Universities of Pennsylvania and Hull. |
| 100 |
POLYMERS THAT MELT ON COOLING
Supervisors Professor G Ungar and Dr M A Shcherbina |
| This anomalous phenomenon has recently been discovered in a group of polymers with an inorganic backbone. The effect has major implications in our understanding of thermodynamics of polymers, but also have practical implications. The material is solid at higher temperatures but rubbery at low temperatures, the exact opposite of the behaviour of all other polymers. It can thus, e.g., be blended with other polymers to compensate for temperature changes in mechanical properties. The project will study the phenomenon in detail, using structural, spectroscopic and dynamic mechanical methods, as well as computer modelling and simulation. |
| 101 |
SELF-ASSEMBLED NANOWIRES AND NANOCOILS
Professor G Ungar and Dr X B Zeng |
| Straight one-dimensional electronic conductors of nanometre thickness can be produced by self-assembly of conjugated organic molecules or macromolecules. The idea is to incorporate them into molecular-scale electronic circuits. This project will utilize highly chiral (left- or right-handed) molecules in order to fabricate self-assembled helical nanowires (nanocoils), potentially new circuit elements in molecular electronic. A part of the project will also be dedicated to investigating the potential use of ceramic nanochannels for this purpose. |
| Dr X Zeng |
| 102 |
ARRANGING METAL NANOPARTICLES WITH LIQUID CRYSTALS
Supervisors: Dr X B Zeng and Professor G Ungar |
| Nanoparticles based on metals, metal oxides or sulphides are currently of great scientific and technological interest. The coverage of nanoparticles with organic groups not only enhances the processability (e.g. solubility) of such systems, but, where suitable functional groups are included, it also allows applications in areas ranging from optics, electronics, and catalysis to biomedical research and medical diagnostics. The novelty of this project is in that the metal nanoparticles will be coated with liquid crystal molecules of different design, so as to achieve previously unavailable modes of 2d and 3d ordering on surfaces and in the bulk. Such use of directed self-assembly would produce arrays and gratings with novel electronic, magnetic and photonic properties. Preliminary studies have already produced several new nanolattices. |
| 103 |
MOLECULAR HONEYCOMBS AND NANOFRAMEWORKS
Supervisors: Dr X B Zeng and Professor G Ungar |
| It has been shown recently that by combining incompatible rigid and flexible segments in one molecule, and adding weakly interacting groups, one can create novel self-assembled organic structures resembling honeycombs and scaffold-like frameworks. These can have different symmetries and can be modified to serve as catalysts, control-release materials or templates for nanoporous ceramics. In the projects these emerging materials will be investigated using X-ray (synchrotron) and neutron scattering and atomic force microscopy – see Science 2005 307 96. Being part of the Eurocores SONS network “SCALES” (http://materials.dept.shef.ac.uk/liquid_crystal), the project will also extend to novel multi-arm star block copolymers, bringing the scale of the nanostructures to that of the wavelength of light. This would enable creation of novel photonic materials for devices which would do to photons what electronic devices do to electrons. These new structures will complement those comprised of molecular networks, also being studied in Sheffield (see e.g. Zeng et al., Nature Materials 2005 4 562). |
| 104 |
SUPRAMOLECULAR QUASICRYSTALS
Supervisors: Dr X B Zeng and Professor G Ungar |
| It has been discovered recently that a quasicrystalline structure with unusual 12-fold rotational symmetry can be created by packing of soft spheres, self-assembled from tree-like molecules (Zeng et al. Nature 2004 428 157). These soft quasicrystals have a structure similar to those found in metal alloys, but are 10-100 times larger in scale by replacing atoms with spherical molecular aggregates, each contains thousands of atoms. This points to the possibility of creating self-assembled quasicrystals with characteristic length at optical scale, which could be useful as photonic band gap materials due to their unusually high rotational symmetry. In the current project, the structure of these soft quasicrystals will be investigated by x-ray and electron diffraction, transmission electron microscopy, atomic force microscopy and computer modelling. |
