Flows found in many situations, including gravel bed rivers, overland flows, and in partially filled pipes, are turbulent. A key issue is the momentum and forces that this turbulent flow imparts on the sediment grains that make up the boundaries of many natural channels. Currently a spatially averaged parameter, termed shear, is used to describe the momentum/force that is transmitted from the turbulent flow into the sediment deposit. The exchange of momentum between the fluid and bed is a key physical process - being able to understand the processes will help understanding of how sediments and pollutants move, and how flows lose energy and so determine flow depths. Most river beds are composed of porous, spatially complex, three-dimensional granular deposits so the spatial and temporal distribution of momentum will control the exchange of pollutants between the flow and the bed and whether individual sediment grains will move. Currently environmental scientists can only measure boundary shear stress in very crude ways, which only provide time and space averaged measurements, many of which rely on empirical parameters that are impossible to determine at a local scale. This project proposes to develop a system that would be able to measure boundary shear stress in a water flow at a grain scale and at a frequency capable of determining the fluctuations in boundary shear stress caused by observed turbulent flow structures. The system uses a concept originally used by aeronautical engineers. The project team will use novel chemistry to create thin coatings capable of being attached to natural sediments that can measure shear stress directly. The new coatings will contain chiral nematic liquid crystals (CLCs), which change colour in response to changes in shear stress. The use of thin film coatings, combined with suitable illumination and image capture techniques, will mean that it is possible to measure, for the first time, the temporal and spatial fluctuating forces on grains in water-worked gravel beds subjected to turbulent depth-limited flows.

Most people have heard of liquid crystals - they are the materials that are used in the flat-panel displays found in lap top computers, mobile phones and some of the most modern television sets. The technology is so successful that last year a liquid crystal display (LCD) was sold for every person on earth. There is always a push for faster, better display devices. These might use lower power, so are more environmentally friendly, or become more complex and faster, perhaps making them useful as specialist optoelectronic devices - things that improve telecommunications and computing. Liquid crystals aren't just high-tech materials though. They are fluids that have both function and order, and are a key component of many biological systems. For example liquid crystals help spider silk to have its amazing strength and flexibility, they cause the beautiful colours in some insects and even play a part in your brain which should be 70% liquid crystalline!The research in this proposal involves new liquid crystal materials at the forefront of technology. The materials we wish to study are being considered for use in a number of new applications where their optical properties or their sensitivity to surfaces might be useful. We can carry out a range of new experiments, including scattering x-rays of very precise energy (Resonant scattering) and measuring tiny changes in light scattered by the liquid crystal (Raman scattering), that will allow us to probe the exact kind of order that is important in our liquid crystal systems. We also want to build an experiment that will allow us to squeeze the liquid crystals to see how compressible they are. We believe that by carrying out this range of experiments and carefully combining all the information we gain, we can test theory and help theoreticians to understand how this important state of matter forms. We have new materials that will allow us to do some of the experiments we are proposing for the first time. Also, the unique combination of experiments that we are proposing will allow us to build a complete picture of whether the layers that we know form in this kind of liquid crystal are important in the process of forming the different types of liquid crystal structure. Understanding how this special kind of liquid crystal orders in the way it does has implications beyond technology. In studying physics or materials science, we try to understand why certain materials act in the way they do so that we can better use their properties, or so that chemists can improve them. Liquid crystals are an example of a fluid state of matter in which the molecules 'self-assemble' and the way in which they do depends very subtly on small changes in molecular structure or composition. How this happens is still not very well understood, despite this topic becoming increasingly important in areas like nanotechnology where materials with function are assembled into tiny structures that then act at a lager scale. Self-assembly is also a vital process in nature where, for example, the fluids we are composed of assemble in such a way that very high-level functions can take place. An important aspect of the research we plan is that we hope to understand how small changes in molecular structures in our systems lead to very large differences in their bulk physical properties. Such research has very broad relevance as it can potentially help us to understand how nature works. This final point isn't just speculative either / we recently used our understanding of liquid crystal optics to suggest how some fish see polarised light (without using Polaroid sunglasses!). There is no question that understanding self-assembly of fluids is important in many areas of science.