Understanding the effects of confinement on near-surface soft nanostructures using neutron and X-ray reflection

The properties of surfaces can be modified extensively by coating them with polymers and surfactants. Examples of this are abundant from the Teflon coating on a frying pan to the sunscreen we wear at the beach. Another familiar aspect of polymers at surfaces is lubrication in an engine that would seize up without its protective coating. The new surfaces we produce through these modifications can, for example, be made strongly adhesive, non-stick, biologically active, anti-bacterial, depending on the coatings used and these can be tailored for each application. In industrial processes, particles such as pigments, paint bases and pharmaceuticals are frequently coated with molecules to control either their processing or end-user properties. While the behaviour of small molecules such as soaps and detergents at these surfaces is well understood, the role of larger molecules such as polymers is not, especially when interacting with surfactants and nanoparticles.When two coated surfaces come together (say when a blood cell adheres to a filtration membrane or when two drops of ink coalesce), what happens at the interface is quite unclear. The actual interlayer forces in the molecular structures that form in these confined spaces have not been studied in detail because making such experimental measurements is very difficult. Understanding these structures in depth will help us develop a detailed picture of polymeric behaviour in these systems. With this knowledge, it should become possible to design novel materials to fulfil these functions rather than rely on serendipity; factors such as environmental impact or cost can then be given greater weight rather than restricting choice to the few materials that are known to work.We also intend to look at advanced uses of structured liquids such as those used in liquid crystal displays. Understanding the interactions of these liquids with solid surfaces will assist in improving switching speed and power consumption which will assist the development of new display technology such as reflective, electronic paper.We are constructing a compression device where a flexible membrane is pushed against a very flat 10cm diameter quartz block. These two surfaces coming together mimic two small particles coming together (such as the cell and membrane or two ink drops we mentioned earlier) but at a larger scale so that we can see what is happening in the solution between them. At the same time that we compress surfaces, we will shine a neutron or X-ray beam through the interfaces to measure the structures in the gap. Neutrons are similar in some respects to X-rays in that they can measure structures with sub-nanometre precision and can pass through many materials allowing us to see inside. The new 2nd Target Station at the ISIS facility in Oxfordshire is one of the places where these experiments will be undertaken.We expect that a polymer that causes flocculation of particles (e.g. for waste water treatment) will have a very different structure compared with a polymer that helps stabilise particles (e.g. for drug delivery). Understanding these structures in detail will help us develop a detailed picture of various phenomena that are observed with polymers including lubrication, stabilisation and flocculation.