In the 20th century plastics became an indispensable part of modern life. Most plastic products are produced by melting polymer materials and moulding them into different shapes. The flow or rheological behaviour of molten polymers is highly sensitive to their molecular architectures and molecular weight distributions. Presence of a small amount of long chain branching structures in commercial polymers can alter their rheological and thus processing properties significantly. Therefore a thorough understanding of the relationship between polymer branching and rheology is of crucial importance to the multi-billion pounds plastics industry. The dominant contributions in defining this relationship come from two respects: entanglement effects among long polymer chains or branches and complexity in branching architectures. The entanglement effects originate from the fact that long polymer chains can not pass through each other. As a consequence, the lateral motion of the chains are suppressed, leading to the extremely long relaxation time and characteristic viscoelastic behaviour of entangled polymers, which are qualitatively different from the viscous behaviour of fast relaxing simple liquids. Theoretical works on entanglement dynamics have been for 40 years primarily based on the tube theory. This model assumes that the motion of a linear polymer chain is restricted to a tube-like region along its contour formed by surrounding chains, similar to a snake slithering through an array of obstacles. Recent tube theories can provide appropriate description of the linear rheology of monodisperse linear polymers, but is facing serious difficulties in describing the branched polymers. Synthesized branched polymers can have various architectures, such as star, H-shaped, comb and Cayley-tree polymers. The commercial polymers, such as metallocene polyethylene resins, can even have branches on branches, i.e., hyperbranching, structures. The branching structures prevent these polymers from sliding in the melt as do the linear chains. Instead a star polymer diffuses by retracting its arms all the way to the branch point, allowing this point to move a short distance, and then stretching out the arms again. This is analogous to an octopus entangled in an array of topological constraints (e.g., a fishing net). The relaxation time of stars thus grows exponentially with the length of the arms, in radical contrast to the power law chain-length dependence of the linear polymers. Polymers with more complicated architectures are assumed to relax in a hierarchical way. The relaxation starts from the retraction of the outermost branch arms and proceeds to inner segments layer by layer till the core of the molecule. Theoretical modelling of the branched polymers needs to address several essential questions including the dynamics of the branch arm retraction, the branch point diffusion and the hierarchical relaxation, as well as the reduced entanglement effects caused by the relaxation of surrounding polymers. The fast grow in computer power and simulation techniques enables us to examine these problems in great details. In this project, we propose to perform molecular dynamics simulations to investigate the relaxation dynamics of model branched polymers at the microscopic level. Special attention will be paid to examine and, if needed, re-formulate the assumptions and analytical expressions used in the current tube theories for describing the above-mentioned dynamic processes. Based on these microscopic understanding, more coarse-grained theoretical models will be developed, which will ultimately allow prediction of dynamics and rheology of general mixtures of branched polymers with arbitrary architectures over many decades of time and length scales.

In order to produce green hydrogen at scale from the electrolysis of water, new electrolysers that are more compatible with intermittent renewably-generated power must be developed. This is because existing electrolysers suffer from two key drawbacks which hampers their adoption for green hydrogen production driven by renewable power sources. Firstly, existing electrolysers do not handle intermittent power inputs effectively. Renewable power sources are by definition intermittent (sometimes the sun shines, and sometimes it doesn't, and when it is shining its intensity on the ground is constantly varying). If connected directly to a solar panel for example, a conventional electrolyser would be operating in constant stop-start mode. This accelerates the degradation of expensive components in the electrolyser and also leads to the production of dangerous mixtures of the hydrogen and oxygen products of electrolysis. As such, conventional electrolysers require significant power management apparatus in order to work safely using renewable power inputs. Without such power management systems, conventional electrolysers would produce dangerous mixtures of hydrogen and oxygen when coupled directly to renewable power sources, which hitherto has been a major barrier to the realisation of a hydrogen production economy driven by renewable power. The second major drawback of conventional systems is their high operational and maintenance costs. State-of-the-art electrolysers contain expensive membranes to try and keep the hydrogen and oxygen products separate, but these degrade rapidly during operation and must be replaced regularly. This adds considerable cost and complexity to long-term electrolyser operation. In this proposal, we will build on the concept of "decoupled electrolysis" to develop a system that can use solar power directly for the electrolysis of water. A decoupled electrolysis approach has the potential to solve both of the key issues preventing greater uptake of electrolysis for green hydrogen production. Indeed, in our preliminary results, we have shown that decoupled electrolysis allows the effective and safe use of power inputs characteristic of renewable sources under conditions where a conventional electrolyser produced a hazardous mixture of hydrogen and oxygen. In contrast, the gases produced by the decoupled system were well within regulatory limits in terms of mixed gas content. We were also able to show that membrane degradation was significantly reduced in a decoupled system relative to a conventional system, suggesting that decoupled electrolysers should require less downtime and incur lower maintenance costs than conventional "coupled" electrolysers. Both of these features could be expected to make electrolysis of water to produce green hydrogen significantly more practical and cost-effective. By leveraging the ability of decoupled electrolysis to allow hydrogen and oxygen generation to take place in separate places, at separate times and at rates that are not connected to each other, we aim in this project to demonstrate the production of pure hydrogen at pressure driven by sunlight. This will open the door to future scale-up of these systems for safe and efficient production of zero-carbon hydrogen driven by renewables.

How from a cloud of dust and gas did we arrive at a planet capable of supporting life? This is one of the most fundamental of questions, and engages everyone from school children to scientists. We now know much of the answer: We know that stars, such as our Sun, form by the collapse of interstellar clouds of dust and gas. We know that planets, such as Earth, are constructed in a disk around their host star known as the planetary nebula, formed by the rotation of the collapsing cloud of dust and gas. We know that 4.5 billion years ago in the solar nebula, surrounding the young Sun, all the objects in our Solar System were created through a process called accretion. And among all those bodies the only habitable world yet discovered on which life evolved is Earth. There is, however, much that we still do not know about how our Solar System formed. Why, for example, are all the planets so different? Why is Venus an inferno with a thick carbon dioxide atmosphere, Mars a frozen rock with a thin atmosphere, and Earth a haven for life? The answer lies in events that predated the assembly of these planets; it lies in the early history of the nebula and the events that occurred as fine-dust stuck together to form larger objects known as planetesimals; and in how those planetesimals changed through collisions, heating and the effects of water to become the building blocks of planets. Our research will follow the evolution of planetary materials from the origins of the first dust grains in the protoplanetary disk, through the assembly of planetesimals within the solar nebula to the modification of these objects as and after they became planets. Evidence preserved in meteorites provides a record of our Solar System's evolution. Meteorites, together with cosmic dust particles, retain the fine-dust particles from the solar nebula. These dust grains are smaller than a millionth of a metre but modern microanalysis can expose their minerals and compositions. We will study the fine-grained components of meteorites and cosmic dust to investigate how fine-dust began accumulating in the solar nebula; how heating by an early hot nebula and repeated short heating events from collisions affected aggregates of dust grains; and whether magnetic fields helped control the distribution of dust in the solar nebula. We will also use numerical models to simulate how the first, fluffy aggregates of dust were compacted to become rock. As well as the rocky and metallic materials that make up the planets, our research will examine the source of Earth's water and the fate of organic materials that were crucial to the origins of life. By analysing the isotopes of the volatile elements Zn, Cd and Te in meteorites and samples of Earth, Moon and Mars we will establish the source and timing of water and other volatiles delivered to the planets in the inner Solar System. In addition, through newly developed methods we can trace the history of organic matter in meteorites from their formation in interstellar space, through the solar nebula and into planetesimals. Reading the highly sensitive record in organic matter will reveal how cosmic chemistry furnished the Solar System with the raw materials for life. Once the planets finally formed, their materials continued to change by surface processes such as impacts and the flow of water. Our research will examine how impacts of asteroids and comets shaped planetary crusts and whether this bombardment endangered or aided the emergence of life. We will also study the planet Mars, which provides a second example of a planetary body on which life could have appeared. Imagery of ancient lakes on Mars will reveal a crucial period in the planet's history, when global climate change transformed the planet into an arid wasteland, to evaluate the opportunity for organisms to adapt and survive and identify targets for future rover and sample return missions.

The process powering the sun can be harnessed as clean and safe fusion energy. Progress in fusion could be accelerated by shrinking the size and cost of reactors and the UK Government has recently announced £220 million to develop such smaller reactors. However, for them to operate continuously for several decades, certain parts of the reactor must be shielded from high energy particles. With currently available shielding materials, these parts will begin to degrade within a matter of weeks or months. My programme of work will develop more efficient shielding materials so that these reactors can operate on a continual basis. Conventional shields use heavy atoms, which reflect the lighter particles; similar to how a ping-pong ball might bounce back off a snooker ball. My research is based on a hybrid approach, combining heavier elements with lighter ones, which instead absorb and dissipate the particle's energy; think now of similarly weighted balls colliding, like a break in snooker. The approach has been proven in theory, but I must now turn this into reality by fabricating and testing real engineering materials. In doing so I will work closely with the UK's leading fusion engineering company, Tokamak Energy, and the UK Atomic Energy Authority, both of whom seek to build energy-producing reactors within the next 10-20 years. My first aim is to fabricate these materials. Because they are very hard and do not melt easily, I will use similar methods to the way other hard materials are made, such as those within a household drill-bit. These are made by compressing powders together at high temperature so that the powders fuse to form a solid material. I will test the properties of the materials like their strength. As part of this I will seek to understand how the geometrical arrangement of the atoms within the material - the so-called "microstructure" - affects these properties. The second aim will be to understand how these materials degrade in the environment of the fusion reactor. They will be subjected to extreme heating, which in some areas of the reactor is similar to what is experienced in a rocket engine. I will test how the material's mechanical strength degrades at these temperatures, just like steel is softened in a blacksmith's furnace to become malleable. At the same time, the materials will also be bombarded by high energy particles in the reactor. This tends to jumble-up the arrangement of the atoms, which can make the materials more brittle; in the same way that when you bend a paperclip back-and forth, it eventually snaps. To test this, I will use specialist particle beam facilities to simulate the damage process. Because the damage only occurs on a small scale (about a tenth the thickness of a human hair) I will use very high-power microscopes to observe the jumbling-up process. I will also perform small-scale mechanical tests on the damaged areas to understand how the jumbling-up effects strength. To interpret these tests, I will work with experts in computer modelling, who can simulate individual "atomic jumps" to work out which sorts of jumps are responsible for the damage. The final aim of the fellowship is to optimise the material's atomic arrangement to improve its damage tolerance. To achieve this, I will engineer the material's building blocks by firstly adding a cement-like layer between blocks, and secondly by flattening the blocks like pancakes. Such engineering is found in nature, where sea-snail shells are built from thinly stacked layers of relatively brittle chalk-like ceramics, with a gluey substance in between. So, when the shell is struck by predators, cracks either stop in the glue, or deflect between the layers of chalk, and the snail survives. By bringing this approach, my work will enable the materials in fusion power plants to withstand even more extreme environments and thus enable them to operate for longer, which will in turn decrease the cost of fusion energy.

The impact of climate change is predicted to be particularly intense in polar regions. Warmer and wetter conditions in the Arctic, where extensive moss dominated habitats are found, could lead to melting of permafrost and an increase in moss growth whilst forests decline. Our existing work has included developing innovative models which use the stable isotope composition of organic matter to provide information about moss growth. This work incorporated both moss preserved for thousands of years in Antarctic peat-moss banks, and desiccation-tolerant mosses that commonly grow on roofs and paths and are rapidly activated following a rain shower. Our previous work has shown that the stable isotope composition of carbon provides a reliable indicator of moss growing season, and the impact of climate change. However other naturally-occurring stable isotope signals in water (e.g 18O in water), associated with precipitation inputs and water vapour exchange, have until now been less well defined as markers of evaporative demand. In this proposal, we will increase our understanding of moss growth dynamics to include how plants respond to different evaporative conditions, how different types of moss grow, what conditions are best for the fixation of carbon dioxide from the atmosphere and growth through the synthesis of organic matter. These developments in moss physiology will be integrated with local weather conditions in models of moss growth that can be applied across large areas to predict periods of plant growth. We will carry out laboratory experiments in which moss growth is manipulated, monitored and measured, using isotope labels and growth responses under different temperature, humidity and drying regimes. We will work on moss species that grow in a range of habitats from wet bog Sphagnums, through hummock forming Polytrichales to desiccation tolerant Syntrichia. At the field scale, the same mosses will be regularly monitored in their natural environment, testing how the experimentally determined dynamics apply within an ecologically relevant setting. The combination of lab and field measurements will firstly allow us to determine the controls on moss organic matter 18O composition as climatic conditions vary. Secondly, remote sensing field measurements will be made from a distance of several metres using newly developed LIFT (laser induced fluouresence transient) technology. By understanding the link between moss growth dynamics and photosynthetic activation over this larger spatial scale we will establish a baseline that will allow remote sensing methodologies, such as measurements from aeroplanes and satellites, to be used to monitor moss performance in the future.